Platinum Group Metals and Compounds;: A symposium sponsored by the Division of Inorganic Chemistry at the 158th meeting of the American Chemical Society (Advances in chemistry series 098)

Platinum Group Metals and Compounds A symposium sponsored by Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0...

Author: U. V. Rao - Symposium Chairman

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Platinum

Group

Metals

and Compounds

A symposium sponsored by Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.fw001

the Division of Inorganic Chemistry at the 158th Meeting of the American Chemical Society, New York, Ν. Y . , Sept. 8-9, 1969. U. V. Rao Symposium Chairman

ADVANCES

IN

CHEMISTRY

SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON, D. C.

1971

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

98

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.fw001

Coden:

ADCSHA

Copyright © 1971 American Chemical Society All Rights Reserved

Library of Congress Catalog Card 76-152,755 ISBN 8412-0135-8 PRINTED IN THE UNITED STATES OF AMERICA In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

A d v a n c e s in C h e m i s t r y Series


Robert F. Gould, Editor

Advisory Board Paul N. Craig Thomas H. Donnelly Gunther Eichhorn Frederick M. Fowkes Fred W. McLafferty William E. Parham Aaron A. Rosen Charles N. Satterfield Jack Weiner

AMERICAN CHEMICAL SOCIETY PUBLICATIONS



FOREWORD

ADVANCES

IN CHEMISTRY

SERIES

w a s f o u n d e d i n 1949 b y the

A m e r i c a n C h e m i c a l S o c i e t y as a n outlet for s y m p o s i a a n d c o l lections of d a t a in s p e c i a l areas of t o p i c a l interest that c o u l d n o t b e a c c o m m o d a t e d in the Society's journals. m e d i u m for s y m p o s i a that w o u l d o t h e r w i s e b e

It p r o v i d e s a fragmented,

t h e i r papers d i s t r i b u t e d a m o n g several journals or not

pub-

l i s h e d at all. P a p e r s are refereed c r i t i c a l l y a c c o r d i n g to ACS e d i t o r i a l standards a n d receive the c a r e f u l a t t e n t i o n a n d p r o c essing c h a r a c t e r i s t i c of ACS p u b l i c a t i o n s . in

ADVANCES

IN CHEMISTRY

SERIES

Papers p u b l i s h e d

are o r i g i n a l c o n t r i b u t i o n s

not p u b l i s h e d elsewhere i n w h o l e o r m a j o r p a r t a n d i n c l u d e reports of research as well as r e v i e w s since s y m p o s i a m a y e m b r a c e b o t h types of

presentation.


Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.pr001

PREFACE

lmost every chemist is aware of the fact that platinum group metal chemistry usually centers around the phenomenon of catalysis. Other interesting phases of the chemistry of the platinum group metals which could be of interest to inorganic chemists are usually obscured by this singular though significant application. When I approached Eugene Rachow, Chairman of the Symposium Planning Committee of the Inor ganic Division of ACS, I had every intention of covering all facets of the platinum group metal chemistry. Because of the limitations of time, I was obliged to limit the symposium to four sessions. The material to be presented at the symposium was divided into four categories: (1) Synthe sis, Structure, Determination, and Study of Magnetic and Thermodynamic Properties of Platinum Group Metal Compounds, (2) Recent Chemistry of σ- and ττ-Bonded Complexes of Platinum Group Metals, (3) Spec troscopic Properties of Platinum Group Metal Compounds, (4) Newer Industrial Aspects of Platinum Group Metals and Their Compounds. Each category, by itself, can be a topic for a separate symposium, and it is hoped that in the future such symposia will be forthcoming. The topics chosen were such that they would cover a broad area of the chemistry of platinum group metals. The session on industrial aspects was included to enable scientists in industry to present their views on the problems that are facing the industry and perhaps stimulate sufficient interest so that newer applications could be developed in the future. It is also hoped that such a forum would enable scientists in industry to summarize broadly the work carried out by them without worry about violation of proprietary nature of the work. I would like to take this opportunity to extend my thanks to all the speakers at the symposium and to all the authors who contributed articles to this volume. I would also wish to express my gratitude to the manage ment of Matthey Bishop, Inc., who kindly permitted me to utilize their time and facilities to arrange this symposium. My special thanks to G. Cohn of Engelhard Industries and L. B. Hunt of Johnson Matthey & Co. for their cooperation and help rendered to find suitable speakers. U. V. RAO

Matthey Bishop, Inc. Malvern, Pa. 19355 December 1970 vii In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

1

M a g n e t i c Properties o f the P l a t i n u m Metals a n d T h e i r A l l o y s H. J. ALBERT and L. R. RUBIN

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

Engelhard Minerals and Chemicals Corp., Newark, N. J. 07105 Although they are paramagnetic, the platinum metals, especially platinum, palladium, and rhodium, are capable of interacting in alloys with other metals to form ferromagnetic or very nearly ferromagnetic materials. Dilute additions of elements of the iron group and its neighbors with platinum and palladium take on enhanced moments which are interpreted as arising from an interaction of the solute moment with the 4d or 5d host electrons. Ferromagnetic and anti-ferromagnetic structures may result from greater additions of the iron group to the platinum metals. Examples are FeRh, Pt Fe, Pd Fe, and PtCo. Compounds of the rare earths with the platinum metals also form magnetic structures with unusual properties. 3

3

*Tphe platinum metals—ruthenium, rhodium, and palladium in the 2nd long row of the periodic system and osmium, iridium, and platinum in the 3rd long row—are all paramagnetic. That is, none of these elements have a permanent magnetic moment associated with it. However, as shown in Table I, the mass susceptibility of these elements varies widely over two orders of magnitude. Further, the "nonmagnetic" platinum metals are the elements immediately beneath the "magnetic" series iron-cobalt-nickel and, of course, are all in the transition group. Platinum, palladium, and rhodium form a number of ferromagnetic alloys with the iron group metals and with manganese. The present paper is not an exhaustive review but presents some of the more interesting magnetic work on the platinum metals which has appeared in the last 10-20 years. Palladium has the highest magnetic susceptibility of the platinum group, and because it is so high it has been termed an "incipient ferromagnet." The implication is that palladium could be induced to become A

1 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2

P L A T I N U M

Table I.

GROUP

M E T A L S

A N D

C O M P O U N D S

Mass Susceptibility of the Platinum Metals (Χ

Ru(+0.427)»

10

- 6

cgs U n i t s )

Rh(+0.9903)

0

Pd(+5.231)

c

c

Os(+0.052) Ir(+0.133) Pt(+0.9712) ° Reprinted from Engelhard Industries Technical Bulletin. Determinations made at 25°C. Determinations made at 20°C. b

6

c

6

e

ferromagnetic.

I n a w e a k l y p a r a m a g n e t i c m a t e r i a l , t h e s u s c e p t i b i l i t y of

the m a t e r i a l is i n d e p e n d e n t of t e m p e r a t u r e .

F i g u r e 1 ( 3 9 ) shows this

to b e q u i t e true f o r r h o d i u m . P a l l a d i u m , o n t h e other h a n d , exhibits a s t r o n g t e m p e r a t u r e d e p e n d e n c e of s u s c e p t i b i l i t y w i t h a p e a k at about Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

7 0 ° K . T h i s has b e e n t a k e n i n the past as évidence f o r a n a n t i f e r r o m a g n e t i c t r a n s i t i o n . H o w e v e r , n e u t r o n d i f f r a c t i o n has s h o w n n o e v i d e n c e of a n t i f e r r o m a g n e t i s m , a n d i t n o w seems l i k e l y that this effect is c a u s e d b y the F e r m i surface of p a l l a d i u m b e i n g associated w i t h a n extremely sharp p e a k i n t h e density-of-states.

T h e s u s c e p t i b i l i t y vs. t e m p e r a t u r e

curve

f o r t h e p a l l a d i u m - 5 % r h o d i u m a l l o y i n d i c a t e s t h e s e n s i t i v i t y of p a l l a d i u m - b a s e d alloys to electron c o n c e n t r a t i o n a n d t h e density-of-states i n r e l a t i o n to the F e r m i l e v e l

(13).

I r o n i m p u r i t i e s g r e a t l y c o m p l i c a t e t h e s u s c e p t i b i l i t y measurements o n p a l l a d i u m . A s n o t e d a b o v e , p a l l a d i u m is close to b e i n g f e r r o m a g n e t i c ,

I200xl0"

6

1000

800

600 mol 400

200

0.

100

200

Temperature,

300

°K

Weiss, J . R. "Solid State Physics for Metallurgists," Pergamon f

Figure 1. The susceptibility (10~ ergs/gauss?/mole) for palladium, rhodium, and paUadium-5% rhodium as a function of temperature (39) e


1.

A L B E R T

Magnetic

A N D R U B I N

50

' ' ΊΟο' '

3

Properties

'

Ι5θ' ' ' T(°K)

ZOO' ' ' 250'


Journal of Applied Physics

Figure 2. Susceptibility vs. temperature for several "pure" palladium samples (17) φ 3 ppm iron, Ο 2 ppm iron, Δ zone refined, solid line less than 1 ppm iron

TCK)

Journal of Applied

Physics

Figure 3. Susceptibility vs. temperature for phtinum with approximately 3 ppm of iron (17)

a n d s m a l l a d d i t i o n s of i r o n w i l l f o r m f e r r o m a g n e t i c alloys w i t h

Curie

temperatures i n t h e c r y o g e n i c range. T h u s , as s h o w n i n F i g u r e 2 ( 1 7 ) , e v e n parts p e r m i l l i o n of i r o n i n p a l l a d i u m m a y b e n o t i c e d r e a d i l y i n s u s c e p t i b i l i t y measurements

at l o w temperatures.

N e u t r o n scattering

measurements h a v e s h o w n that i r o n i m p u r i t i e s h a v e a n effect f a r b e y o n d the n e a r e s t - n e i g h b o r p a l l a d i u m atoms, e x t e n d i n g p e r h a p s to t h e nearest 100 p a l l a d i u m atoms, a c c o u n t i n g f o r the extreme s e n s i t i v i t y of p a l l a d i u m to i r o n i m p u r i t i e s

(28).

P l a t i n u m , F i g u r e 3 (17), shows b e h a v i o r s i m i l a r t o t h a t of p a l l a d i u m b u t its s u s c e p t i b i l i t y a n d the effect of i r o n i m p u r i t i e s are m u c h s m a l l e r . T h e s m a l l p e a k at 100°Κ is analogous to that f o r p a l l a d i u m .


4

P L A T I N U M

GROUP

M E T A L S

A N D

C O M P O U N D S

Local Moments C o n s i d e r a b l e research i n recent years has b e e n c a r r i e d o u t o n the m a g n e t i c properties of alloys of elements of the s e c o n d a n d t h i r d l o n g r o w s of the p e r i o d i c table w i t h s m a l l amounts of elements i n the

first

l o n g r o w . S o m e of the most i n t e r e s t i n g results of this w o r k are c e n t e r e d o n t h e p l a t i n u m metals. O n e aspect of the results is g i v e n i n F i g u r e 4

(11),

s h o w i n g the m a g n e t i c m o m e n t of a n i r o n a t o m d i s s o l v e d i n the s e c o n d r o w t r a n s i t i o n metals. A n e n h a n c e m e n t of the i r o n m o m e n t is a p p a r e n t for alloys w i t h electron concentrations of a b o u t 5.5 to 7 a n d 8.25 to 9. F o r electron concentrations f r o m 9 to 10.25 there is a v e r y l a r g e e n h a n c e m e n t , the m o m e n t e x c e e d i n g t h a t of i r o n i n its b u l k state ( a b o u t 2.2

μ ). Β


A l l o y s s h o w i n g this large e n h a n c e m e n t are r e g a r d e d as h a v i n g " g i a n t moments."

E n h a n c e m e n t effects of the solute m o m e n t h a v e b e e n f o u n d

i n m a n y a l l o y systems, i n c l u d i n g C r (2), C o (9, 10, 38)

M n (2),

F e (10,

11, 18),

and

i n p a l l a d i u m a n d alloys of p a l l a d i u m a n d r h o d i u m . T h e

e x p e r i m e n t a l t e c h n i q u e w i d e l y u s e d to s h o w the existence of s u c h l o c a l m o m e n t s is the m e a s u r e m e n t of s u s c e p t i b i l i t y . T h e s u s c e p t i b i l i t y is m e a s u r e d as a f u n c t i o n of t e m p e r a t u r e , u s u a l l y f r o m 1.4° Κ to r o o m t e m p e r a ture or higher.

T h e d a t a f r o m alloys w i t h

a

temperature-dependent

s u s c e p t i b i l i t y are fitted to a C u r i e - W e i s s t y p e of c u r v e w h i c h leads to 14

3

4

Y

Zr

5

6

Nb

7

Mo

Re

ELECTRON

8

9

10

11

Ru

Rh

Pd

Ag

Ν

CONCENTRATION

Physical Review

Figure 4. iron atom metals and and alloy)

Magnetic moment in Bohr magnetons of an dissolved in various second row transition alloys {one atomic per cent iron in each metal as a function of electron concentration (11)



1.

A L B E R T

A N D RUBIN

Os . I o.e 0

4

r

Magnetic

I

5

Properties

r

COMPOSITION

p

(ATOMIC

P E R

t

C E N T )

Journal of Applied

Physics

Figure 5. Susceptibility per mole for alloys containing one atomic per cent iron at 3 different temperatures (18) the i n t e r p r e t a t i o n that a l o c a l m o m e n t exists o n the solute a t o m a n d p e r mits the c a l c u l a t i o n of the m o m e n t associated w i t h the a l l o y . A l l o y s of i r i d i u m a n d p l a t i n u m w i t h s i m i l a r s m a l l amounts of i r o n also e x h i b i t e n h a n c e m e n t effects a n d a giant m o m e n t i n the case of i r o n i n p l a t i n u m a n d p l a t i n u m - r i c h alloys as s h o w n i n F i g u r e 5

(18).

It is o b v i o u s that, i n v i e w of the l a r g e m e a s u r e d m o m e n t s o n the solute atoms, there is m o r e i n v o l v e d t h a n s i m p l y the m a g n e t i c

moment

of the solute a t o m . T h e postulate most w i d e l y u s e d suggests a m o d e l i n w h i c h the m o m e n t o n the solute atoms interacts w i t h the m a g n e t i c m o ments o n the i t i n e r a n t 4d or 5d electrons of the host m e t a l . T h i s i n t e r a c t i o n p r o d u c e s a p o l a r i z a t i o n of the spins i n the 4d or 5d b a n d , at t h e same t i m e a l i g n i n g the l o c a l i z e d m o m e n t s on the solute atoms i n the same d i r e c t i o n as the p o l a r i z e d d-electrons.


6

P L A T I N U M

GROUP

M E T A L S

A N D

C O M P O U N D S

U s i n g this l o c a l m o m e n t m o d e l , a n d u s i n g b a n d t h e o r y or its v a r i a tions, a n u m b e r of w o r k e r s h a v e b e e n a b l e to f o r m u l a t e expressions w h i c h represent the m e a s u r e d m a g n e t i c d a t a r e a s o n a b l y w e l l , at least for the case w h e r e w e l l - l o c a l i z e d m o m e n t s are d e v e l o p e d o n the solute atoms (11,

18).

H o w e v e r , c o n s i d e r a b l y m o r e d a t a has b e c o m e a v a i l a b l e o n

o t h e r properties of d i l u t e a l l o y s , i n c l u d i n g d a t a o n resistivity a n d specific heat, n e u t r o n scattering, v a r i o u s m a g n e t i c resonance experiments, M o s s b a u e r measurements, K o n d o effect,

a n d the l i k e .

Measurements have

b e e n e x t e n d e d also to alloys of m a n y other systems besides those i n v o l v -


i n g the p l a t i n u m metals.

Journal of Applied Physics

Figure 6. ceptibility,

(a) Magnetization (at 5 KOe) and inverse initial sus(b) Electrical resistivity of ordered FeRh for increasing (%) and decreasing (O) temperature (25)


1.

A L B E R T

A N D

R U B I N

Magnetic

7

Properties

T h e scope of this r e v i e w p r e c l u d e s a d e s c r i p t i o n of these d a t a , b u t the results of some of these experiments h a v e s h o w n weaknesses i n t h e o r i g i n a l b a n d m o d e l a p p r o a c h (9, 20, 34). ments (21,

22, 26)

H o w e v e r , n e w e r t h e o r e t i c a l treat-

are p r o v i d i n g m o r e i n s i g h t i n t o the p r o b l e m .

The

subject of l o c a l i z e d m a g n e t i c states i n d i l u t e m a g n e t i c alloys is s t i l l i n a state of v e r y a c t i v e r e s e a r c h a n d t h e o r e t i c a l d e v e l o p m e n t , as s h o w n b y the p r o g r a m s of e v e n the most recent m a g n e t i c conferences, s u c h as the Fifteenth A n n u a l Conference

on Magnetism and Magnetic Materials,

P h i l a d e l p h i a , P a . , N o v e m b e r 1969.


Ordered Alloys I n a d d i t i o n to the d i l u t e alloys a l r e a d y discussed, there are a n u m b e r of alloys of the metals of the p l a t i n u m g r o u p w i t h manganese,

iron,

cobalt, a n d n i c k e l w h i c h have m a g n e t i c properties b a s e d o n t h e f o r m a t i o n of o r d e r e d structures at some p a r t i c u l a r c o m p o s i t i o n . C o n s i d e r i n g i r o n alloys first, the i r o n - r h o d i u m system is a n interesti n g e x a m p l e of m a g n e t i c o r d e r i n g . E a r l y m a g n e t i c measurements i n the system (16)

established that alloys of a b o u t 50 a t o m i c %

rhodium in-

creased i n m a g n e t i z a t i o n as t h e i r t e m p e r a t u r e was r a i s e d t h r o u g h a c r i t i c a l v a l u e . Since 1960, a n u m b e r of w o r k e r s (23, 25, 36) change is o w i n g to a

first-order

h a v e s h o w n t h a t this

a n t i f e r r o m a g n e t i c ( A F M ) to f e r r o m a g -

n e t i c ( F M ) t r a n s i t i o n w i t h i n c r e a s i n g t e m p e r a t u r e , the t r a n s i t i o n t e m p e r a t u r e for a 52 a t o m i c % Figure 6 (25).

r h o d i u m b e i n g a b o u t 350°K, as s h o w n i n

X - r a y d i f f r a c t i o n studies h a v e s h o w n that the c r y s t a l

structure a b o v e a n d b e l o w the t r a n s i t i o n t e m p e r a t u r e is a n o r d e r e d C s C l type, the t r a n s i t i o n b e i n g a u n i f o r m r a p i d v o l u m e e x p a n s i o n of about 1 % w i t h increasing temperature.

C h a n g e s i n l a t t i c e d i m e n s i o n s i n this t y p e

of t r a n s f o r m a t i o n r e s u l t f r o m the differences b e t w e e n the magnetoelastic expansion of the f e r r o m a g n e t i c a l l y o r d e r e d lattice a n d the c o n t r a c t i o n o w i n g to the a n t i f e r r o m a g n e t i c lattice. M e a s u r e m e n t s of the l o w - t e m p e r a t u r e specific heat of i r o n - r h o d i u m alloys a n d i r o n - r h o d i u m - p a l l a d i u m alloys a n d of e n t r o p y changes of the t r a n s i t i o n h a v e s h o w n that the difference i n t h e energies of the F M a n d A F M state is r e l a t i v e l y s m a l l . T h i s suggests a m o d e l i n w h i c h b e l o w the t r a n s i t i o n t e m p e r a t u r e i n the A F M state, r h o d i u m atoms, b y s y m m e t r y , h a v e no net field

exchange

exerted b y the i r o n atoms a n d the energy is d o m i n a t e d b y

iron-

i r o n interactions. A b o v e the t r a n s i t i o n t e m p e r a t u r e , i n the F M state, the r h o d i u m atoms are p o l a r i z e d b y a n exchange field w h i c h i n d u c e s a s i g nificant l o c a l m o m e n t o n the r h o d i u m atoms.

This introduces

another

e n e r g y t e r m w h i c h , i f the s u s c e p t i b i l i t y of the r h o d i u m atoms is l a r g e e n o u g h , w i l l a c c o u n t for the c h a n g e to the F M state (-23).



P L A T I N U M

300

GROUP

M E T A L S

A N D

C O M P O U N D S

400 Τ (°K) Journal of Applied

Figure

7.

Magnetization in a 12.5 KOe field of FeRh line is for the bulk alloys (27).

filings.

Physics

The dashed

A n i n t e r e s t i n g effect i n i r o n - r h o d i u m alloys is n o t e d i n c o l d - w o r k i n g the a l l o y . F i l i n g a n a l l o y to m a k e p o w d e r is a c o n v e n i e n t w a y of c o l d w o r k i n g . M a g n e t i c measurements o n filings are s h o w n i n F i g u r e 7

(27).

S t a r t i n g at p o i n t A , the a l l o y is c o o l e d o 7 0 ° K a n d t h e n h e a t e d to 500°K. l

I t is e v i d e n t t h a t i n the c o l d - w o r k e d a l l o y there is no trace of the A F M to F M t r a n s i t i o n i n this range. B e t w e e n 500° to 700 ° C , a n o r m a l C u r i e p o i n t b e h a v i o r emerges a n d , o n c o o l i n g , the reappears.

first-order

transformation

X - r a y d i f f r a c t i o n measurements o n the filings i n d i c a t e d t h a t

i n the as-filed c o n d i t i o n the filings h a v e a d i s o r d e r e d fee structure, b u t q u e n c h i n g f r o m temperatures as h i g h as 1 4 0 0 ° C d i d not result i n the a p p e a r a n c e of the fee structure. F i r s t - o r d e r transitions also exist for the compositions P t F e , b a s e d o n the C u A u - t y p e structure. 3

3

P d F e and 3

I n the o r d e r e d state, the

f o r m e r a l l o y is f e r r o m a g n e t i c a n d the latter is a n t i f e r r o m a g n e t i c .

Inter

m e d i a t e compositions b a s e d o n F e ( P d , P t ) h a v e s h o w n the existence of 3

a state at l o w temperatures i n w h i c h , s t i l l b a s e d o n the o r d e r e d C u A u 3

structure, the i r o n m o m e n t s m o v e i n t o a " c a n t e d " s t r u c t u r e as s h o w n i n F i g u r e 8 (24).

F o r the c o m p o s i t i o n F e P d i . P t i . , the t r a n s i t i o n f r o m a 6

4


1.

A L B E R T

Magnetic

A N D R U B I N

9

Properties

s i m p l e f e r r o m a g n e t i c state to this f e r r i m a g n e t i c state w i t h c a n t e d i r o n m o m e n t s occurs at a b o u t 140 °K. T h e a l l o y P t F e w i t h a d d e d i r o n is a n i n t e r e s t i n g case b y itself ( 1 ). 3

T h e o r d e r e d a l l o y is a n t i f e r r o m a g n e t i c w i t h f e r r o m a g n e t i c sheets of i r o n atoms a r r a n g e d o n ( 1 1 0 )

planes a n t i f e r r o m a g n e t i c a l l y a l o n g the

[001]

axis. A s the i r o n content is i n c r e a s e d over the s t o i c h i o m e t r i c 25 a t o m i c % , a different A F M structure appears w i t h the sheets a r r a n g e d o n ( 100 ) planes. A t 30 a t o m i c % i r o n , this structure p r e d o m i n a t e s . B e t w e e n these t w o extremes, b o t h types of s t r u c t u r e coexist.

F r o m neutron diffraction

e x p e r i m e n t s , i t is c o n c l u d e d t h a t phase coherence of the t w o structures occurs o v e r m a n y u n i t cells a n d t h a t there is a n i n t e r t w i n i n g of t h e t w o structures r a t h e r t h a n s e p a r a t i o n i n t o d o m a i n s

of

one

or

the

other


structure. T h e platinum—cobalt system is e s p e c i a l l y i m p o r t a n t i n that i t has the o n l y p r e c i o u s m e t a l a l l o y ever to b e d e v e l o p e d f o r p r a c t i c a l use of its m a g n e t i c p r o p e r t i e s . stoichiometric P t C o .

T h i s a l l o y is b a s e d o n s t o i c h i o m e t r i c or n e a r -

It is d i s t i n g u i s h e d b y a v e r y h i g h - e n e r g y p r o d u c t ,

a r e l a t i v e l y l o w r e m a n e n c e , a n d h i g h c o e r c i v i t y . F i e l d s of 30,000 oersteds or h i g h e r are r e q u i r e d for s a t u r a t i o n a n d P t C o magnets are r e g u l a r l y p r o d u c e d w i t h e n e r g y p r o d u c t s greater t h a n 9 m i l l i o n

gauss-oersteds,

coercive forces of 4300 oersteds, a n d r e m a n e n c e near 6400 gauss.

•

Fe

°Pd,Pt Journal of Applied

Figure

8.

Low-temperature canted-ferrimagnetic ofFePd^Pt^ (24)

Physics

structure


FePt

10

P L A T I N U M

DISORDERED

CUBIC

GROUP

M E T A L S

ORDERED

{ll0}

c

A N D

C O M P O U N D S

TETRAGONAL

II ( I O I ) t


C

Figure

9.

Crystallographic relationships disordered and ordered PtCo

between

is i s o m o r p h o u s to P t C o a n d p r e s u m a b l y shares m a g n e t i c h a r d e n i n g m e c h anisms. It has never b e e n u s e d p r a c t i c a l l y because

its c o e r c i v i t y a n d

e n e r g y p r o d u c t s are l o w e r t h a n those of P t C o . P t C o is a n o r d e r i n g a l l o y , f o r m i n g a f a c e - c e n t e r e d - t e t r a g o n a l t y p e structure (c/a tice (31).

CuAu-

— 0.98) f r o m a d i s o r d e r e d face-centered c u b i c l a t -

M a x i m u m c o e r c i v e force a n d m a x i m u m energy p r o d u c t are

a c h i e v e d at less t h a n c o m p l e t e o r d e r , a n d at different stages i n the a p p r o a c h to c o m p l e t e order.

O r d e r i n g starts i n the d i s o r d e r e d a l l o y w i t h

the f o r m a t i o n of a system of o r d e r e d platelets, e a c h c o n t a i n i n g a tetrag o n a l c-axis p a r a l l e l to one of the o r i g i n a l o r t h o g o n a l c u b e axes. are (110)

These

platelets; that is, they are not p a r a l l e l to the " c u b e faces" i n

the d i s o r d e r e d m a t e r i a l . I n a n y g i v e n r e g i o n , p r i m a r i l y as a n a c c o m m o d a t i o n to s t r a i n , o n l y t w o of the three possible p l a t e l e t orientations o c c u r F i g u r e 9 s u m m a r i z e s the c r y s t a l l o g r a p h i c aspects of t h i s system.

(8).

E l e c t r o n m i c r o s c o p i c a n d field i o n m i c r o s c o p i c w o r k has s h o w n t h a t m a x i m u m c o e r c i v i t y is a c h i e v e d i n the t e t r a g o n a l phase w i t h p l a t e l e t w i d t h of 2 0 0 - 5 0 0 angstroms a n d w i t h p l a t e l e t thickness of a b o u t 20 angstroms (30, 33).

T h e d i r e c t i o n of easy m a g n e t i z a t i o n ( c - a x i s ) is n o t i n the p l a n e of

the platelet. T h e degree of t r a n s f o r m a t i o n is f a r f r o m c o m p l e t e at m a x i m u m p r o p e r t i e s , p e r h a p s as little as 5 0 % t r a n s f o r m a t i o n b y v o l u m e

(32).

T h e s a t u r a t i o n m a g n e t i z a t i o n of the d i s o r d e r e d a l l o y is 43.5 gauss c m / g m at 30,000 oersteds (14). 3

T h e m a x i m u m internal magnetization


1.

A L B E R T

320


Magnetic

A N D R U B I N

220

11

Properties

340

0

20

40

200

180

160

f+0

Engelhard Industries Technical Bulletin

Figure 10.

Magnetic anisotropy in a PtCo single crystal (37)

Journal

of Applied

Physics

Figure 11. Crystallite distribution in ordered PtCo (8)


12

P L A T I N U M

GROUP

M E T A L S

A N D

C O M P O U N D S

of the o r d e r e d phase has b e e n estimated as 3 5 - 4 0 % l o w e r t h a n t h a t of the d i s o r d e r e d phase (14).

T h e average m a g n e t i c m o m e n t o f d i s o r d e r e d

P t C o at r o o m t e m p e r a t u r e is 1.04 b o h r magnetons w i t h a s p h e r i c a l d i s t r i b u t i o n of m o m e n t ( 8 ) .

T h e easy m a g n e t i z a t i o n d i r e c t i o n i n the or-

d e r e d phase corresponds

to its c-axis a n d the a n i s o t r o p y constant is

a p p r o x i m a t e l y 50 m i l l i o n e r g / c m

3

(8).

S i n g l e - c r y s t a l w o r k b y W a l m e r (37)

(on a fully-ordered crystal)

s h o w e d a m a x i m u m of the coercive force i n the 111 d i r e c t i o n a n d m i n i m a i n the 110 a n d 100 d i r e c t i o n s , the 100 m i n i m u m b e i n g the l o w e r of t h e t w o (Figure 10).

W o r k b y Brissonneau a n d coworkers (8)

o n the d i s t r i b u -

t i o n of platelets i n c o m p l e t e l y - o r d e r e d P t C o has l e d to a m o d e l s h o w n i n F i g u r e 11, w h e r e i n e a c h z o n e s h o w n i n the figure contains a f u l l y Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

d e v e l o p e d n e t w o r k of ( 110) platelets o r i e n t e d i n t w o of the three p o s s i b l e orthogonal directions. T h e z o n e m o d e l p r o p o s e d b y B r i s s o n n e a u is consistent n o t o n l y w i t h his o w n field i o n m i c r o s c o p i c observations, b u t also w i t h l a r g e r scale a n d often p u z z l i n g p h e n o m e n a observed.

P t C o magnets, for instance, f o r m

B i t t e r patterns o n a scale q u i t e easily v i s i b l e u n d e r a l i g h t m i c r o s c o p e . B i t t e r patterns d o not fit the p i c t u r e of a " f i n e - p a r t i c l e " h a r d e n i n g m e c h a n i s m unless t h e y also d e s c r i b e a l a r g e r scale p h e n o m e n o n , s u c h as B r i s sonneau zone boundaries. B e c a u s e of the s e n s i t i v i t y of the platelets to strain energy, t h e i r n u c l e a t i o n s h o u l d be sensitive to the w o r k i n g h i s t o r y of the b i l l e t s f r o m w h i c h the a l l o y s p e c i m e n is m a d e , a n d , n o t s u r p r i s i n g l y , P t C o responds w e l l to c o l d w o r k i n g b e f o r e heat t r e a t i n g . W o r k b y S h i m i z u a n d H a s h i m o t o (35),

w h o t e m p e r e d P t C o u n d e r elastic stress f a r b e l o w its elastic

l i m i t , has s h o w n that the a l l o y develops

considerably lower coercivity

Journal of Applied

Physics

Figure 12. Effects of compressive and tensile stresses on PtCo hysteresis curves (35)


1.

A L B E R T

Magnetic

A N D RUBIN

Δ

MRu

2

RARE-EARTH


13

Properties

ELEMENT

I NM R U

2

, M 0S2t Μ ΐ Γ

2

Physical Review

Figure

13. Curie temperatures for MX compounds (M = rare earth, X = Ru, Os, or Ir) (7) 2

( a n d higher remanence)

i n the direction of the a p p l i e d

compressive

stress t h a n at r i g h t angles to i t ( F i g u r e 1 2 ) . T h e y also r e p o r t t h e c o n verse to b e true w h e n tensile stress is a p p l i e d .

Platinum Metal—Rare Earth Alloys T h e m a g n e t i c m o m e n t s o f rare e a r t h elements a r e c a u s e d b y t h e u n p a i r e d electrons i n t h e i r 4f shells. T h e s e shells" are s h i e l d e d b y t h e outer shells so t h a t c h e m i c a l b o n d i n g h a s r e l a t i v e l y l i t t l e effect o n t h e m a g n e t i c m o m e n t s o f these elements. L a v e s phases o f c o m p o s i t i o n M B

2

T h e rare earths f o r m a series o f

( M = rare e a r t h , Β == p r e c i o u s m e t a l )

w h i c h share t h e c h a r a c t e r i s t i c of f e r r o m a g n e t i c c o u p l i n g a t l o w t e m p e r a tures ( 7 ) . F i g u r e 13 shows t h e C u r i e t e m p e r a t u r e s o f a series o f corn-

Table II.

Θ, °K

Compound PrRu PrRh PrOs Prlr PrPt GdRh Gdlr GdPt

40 8.6 >35 18.5 7.9 >77 >77 >77

2 2

2

2

2

2

2

2

° Reprinted from

Ferromagnetic Curie Points

Acta

Crystallographica

a

Compound

Θ, °K

NdRu NdRh Ndlr NdPt

35 8.1 11.8 6.7

2 2

2

2

{12).


14

P L A T I N U M

-12

-8 -4 H, MAGNETIC

GROUP

0 F I E L D IN

M E T A L S

A N D

4 8 KILO-OERSTEDS

C O M P O U N D S

12


(a)

-8

-4

0

4

H, MAGNETIC FIELD IN

8

ΚILO - OERSTEDS

(b) Journal of Applied Physics

Figure 14. Hysteresis loops for 2 GdRu -CeRu ing (a) superconductivity and ferromagnetism, ductivity alone (4) 2

pounds where Β = MgCu

2

2

alloys show (b) supercon

R u , O s , a n d I r . T h e s e c o m p o u n d s f o r m i n the c u b i c

( C 1 5 ) o r the h e x a g o n a l M g Z n

2

( C 1 4 ) structures ( 7 ) .

The Curie

p o i n t is h i g h e s t w i t h c o m p o u n d s c o n t a i n i n g G d a n d decreases w i t h l a r g e r o r s m a l l e r a t o m i c n u m b e r s of the r a r e earths ( F i g u r e 1 3 ) . S i m i l a r results have been obtained w i t h Β =

R h or P t (12)

(Table II).

The variation

i n C u r i e temperatures results p r i n c i p a l l y f r o m the i n t e r a c t i o n b e t w e e n the spins of the 4f shells of the rare earths a n d the c o n d u c t i o n electrons. P s e u d o b i n a r y alloys of ( C e R u - G d R u ) (4), 2

(GdRu^ThRujî)

(6),

(GdOs -LaOs ) 2

2

2

(5),

(YOs -GdOs ) 2

2

(29),

a n d p e r h a p s some others


1.

A L B E R T

A N D

Magnetic

R U B I N

15

Properties

s h o w s i m u l t a n e o u s f e r r o m a g n e t i c a n d s u p e r c o n d u c t i n g p r o p e r t i e s over a l i m i t e d range of c o m p o s i t i o n .

T h e system G d R u

2

in CeRu

2

has

been

s t u d i e d extensively. T h i s system shows a s u p e r c o n d u c t i n g t r a n s i t i o n w h e n the c o n c e n t r a t i o n of G d R u more than 6 %

GdRu

2

2

is less t h a n 10 a t o m i c % .

c r e a s i n g w i t h c o n c e n t r a t i o n (4). 8 and 4 % G d R u

2

Alloys containing

are f e r r o m a g n e t i c w i t h C u r i e t e m p e r a t u r e s i n F i g u r e 14 shows hysteresis loops

for

a l l o y s , the latter b e i n g s u p e r c o n d u c t i n g a n d the f o r m e r

being simultaneously superconducting and ferromagnetic.

Both

loops

s h o w the e x c l u s i o n of field c h a r a c t e r i s t i c of s u p e r c o n d u c t i n g m a t e r i a l s ,

Table III.

Curie Temperature and Coercive Force of R s P d Compounds (3)


2

Θ, °K

Compound Gd Pd 6

Hc(at

4.2°K)oe

335

2

Tb5.10Pd1.90

~30

12,800

Dy5.07Pd1.93

~25

9,700

H o . o P d i •96

~10

1,300

5

4

i.e., n e g a t i v e slope o n i n i t i a l m a g n e t i z a t i o n a n d n e g a t i v e s l o p e n e a r r e m a nence i n the first q u a d r a n t . T h e n o r m a l or n o n f e r r o m a g n e t i c s u p e r c o n d u c t o r exhibits a " r e m a n e n c e " a t t r i b u t e d to " f r o z e n - i n " flux. T h e m a g n e t i z a t i o n c u r v e for the f e r r o m a g n e t i c ( 8 % )

a l l o y lies w e l l a b o v e that

c a l c u l a t e d for a p a r a m a g n e t i c m a t e r i a l of the same G d content, a n d the r e m a n e n c e is also w e l l a b o v e that e x p e c t e d for a p a r a m a g n e t i c s u p e r conductor.

I t is q u e s t i o n a b l e w h e t h e r s u p e r c o n d u c t i v i t y a n d f e r r o m a g -

n e t i s m exist i n the same d o m a i n s i n a g i v e n s p e c i m e n .

T h e minor loop

P Q R S shows t h a t some s u p e r c o n d u c t i v i t y s t i l l exists i n parts of the a l l o y after s u p e r c o n d u c t i v i t y as a w h o l e has b e e n d e s t r o y e d . C o m p o u n d s of n o m i n a l c o m p o s i t i o n Μ Β , w h e r e M is a g a i n a r a r e δ

2

earth ( G d , T b , H o , D y ) a n d Β a precious m e t a l (Pt, P d ) , show m a g netizations close to those c a l c u l a t e d f r o m t h e m o m e n t s of the r a r e e a r t h atoms

(3).

Gd Pd 5

2

is a soft m a g n e t i c m a t e r i a l w i t h a c o e r c i v e

force

less t h a n 100 oersteds b u t w i t h a h i g h s a t u r a t i o n associated w i t h the h i g h m o m e n t of G d ( 3 ) .

T a b l e I I I s u m m a r i z e s the p e r m a n e n t m a g n e t i c p r o p

erties of the p a l l a d i u m alloys. T h e p l a t i n u m alloys are i s o s t r u c t u r a l a n d h a v e t h e same C u r i e t e m p e r a t u r e s ( 19).

E n e r g y p r o d u c t s for T b P d a n d

D y P d at 4.2°K are 20 X

1 0 gauss-oersteds, r e s p e c t i v e l y

5

(3).

1 0 a n d 26 X 6

5

6

W h i l e these e n e r g y p r o d u c t s are h i g h e r t h a n p l a t i n u m - c o b a l t , the

l o w C u r i e t e m p e r a t u r e s p r e c l u d e use of these c o m p o u n d s

i n the u s u a l

platinum-cobalt applications.



16

PLATINUM GROUP METALS AND COMPOUNDS

Literature Cited (1) Bacon, G. E., Crangle, J., Proc. Roy. Soc. 1963, A272, 387. (2) Barton, E. E., Claus, H., private communication. (3) Berkowitz, A. E., Holtzberg, F., Methfessel, S.,J.Appl. Phys. 1964, 35, 1030. (4) Bozorth, R. M., Davis, D. D., J. Appl. Phys. 1960, 31, 321S. (5) Bozorth, R. M., Davis, D. D., Williams, A. J., Phys. Rev. 1960, 119, 1570. (6) Bozorth, R. M., Matthias, B. T., Davis, D. D., Proc. Intern. Conf. Low Temp. Phys., 7th, Toronto, Canada, 1960, 1961, p. 385. (7) Bozorth, R. M., Matthias, B. T., Suhl, H., Corenzwit, E., Davis, D. D., Phys. Rev. 1959, 115, 1595. (8) Brissonneau, P., Blanchard, Α., Schlenker, M., Laugier, J., J. Appl. Phys. 1969, 39, 1266. (9) Brog, K.C.,Jones, W. H., Booth, J. G.,J.Appl.Phys. 1967, 38, 1151. (10) Cape, J. Α., Hake, R. R., Phys. Rev. 1965, 139, A142. (11) Clogston, A. M.,etal.,Phys. Rev. 1962, 125, 541. (12) Compton, V. B., Matthias, B. T., Acta Cryst. 1959, 12, 651. (13) Doclo, R., Foner, S., Narath, Α.,J.Appl.Phys. 1969, 40, 1206. (14) Dunaev, F. N., Kalinin, V. M., Kryokov, I. P., Maisinovich, V. I., Fiz. Metal i Metaloved. 1965, 20, 460. (15) Engelhard Ind. Tech.Bull.VI, No. 3, December, 1965. (16) Fallot, M., Hocart, R., Rev. Sci. 1939, 77, 498. (17) Foner, S., Doclo, R., McNiff, E. J., Jr.,J.Appl.Phys. 1968, 39, 551. (18) Geballe, T. H.,etal.,J.Appl.Phys. 1965, 37, 1181. (19) Holtzberg, F., Methfessel, S. J., U. S. Patent 3,326,637 (1967). (20) Knapp, G. S.,J.Appl.Phys. 1967, 38, 1267. (21) Knapp, G. S., Phys. Letters 1967, 25A, 114. (22) Kondo, J., Phys. Rev. 1968, 169, 437. (23) Kouvel, J. S.,J.Appl.Phys. 1966, 37, 1257. (24) Kouvel, J. S., Forsyth, J. B.,J.Appl.Phys. 1969, 40, 1359. (25) Kouvel, J. S., Hartelius, C.C.,J.Appl.Phys. 1962, 33, 1343. (26) Lederer, P., Mills, D. L., Phys. Rev. 1968, 165, 837. (27) Lommel, J. M., Kouvel, J. S.,J.Appl. Phys. 1967, 38, 1263. (28) Low, G. G., Holden, T. M., Proc. Phys. Soc. 1966, 89, 119. (29) Matthias, B. T., U. S. Patent 2,970,961 (1961). (30) Mishin, D. D., Greshishkin, R. M., Phys. Status Solidi 1967, 19, K1-K3. (31) Newkirk, J. B., Geisler, A. H., Martin, D. L., Smoluchowski, R.,J.Metals 1950, 188, 1249. (32) Rabinkin, A. G., Tyapkin, Yu. D., Yamaleev, Κ. M., Fiz. Metal i Metaloved. 1965, 19, 360. (33) Ralph, B., Brandon, D. G., Proc. European Conf. Electron Microsco 3rd, Prague 1964 (A) 303. (34) Sarachik, M. P., Phys. Rev. 1968, 170, 679. (35) Shimizu, S., Hashimoto, E.,J.Appl. Phys. 1968, 39, 2369. (36) Tu, P.,etal.,J. Appl. Phys. 1969, 40, 1368. (37) Walmer, M. L., Engelhard Ind. Tech.Bull.1962, 2, 117. (38) Walstedt, R. E., Sherwood, R.C.,Wernicke, J. H., J. Appl. Phys. 1968, 39, 555. (39) Weiss, R. J., "Solid State Physics for Metallurgists," p. 323, Pergamon, New York, 1963. RECEIVED January 16, 1970.


2

Platinum Metal Chalcogenides


AARON WOLD Brown University, Providence, R. I. 02912

A number of binary platinum metal chalcogenides show interesting electrical and magnetic properties. These are classified according to structure types and their properties related to the formal valence of the platinum metal. A simple one-electron model proposed by Goodenough to explain the properties of the first row transition metal chal cogenides can be applied to the corresponding platinum metal compounds. This theory is successful in correlating new experimental data on these compounds—e.g., crysta structure, resistivity, Seebeck coefficient, and magnetic susceptibility. *"phe electrical and magnetic properties of simple binary platinum metal oxides (15, 19), as well as a number of ternary compounds (4), have shown that these materials can be of considerable interest to both solid state chemists and physicists. A number of the platinum metal oxides are remarkably good electrical conductors and, in addition, magnetic ordering has been observed (4) for several perovskites containing ruthenium. Many of these compounds can be prepared in the form of single crystals (IS), making them suitable for both transport and magnetic measurements. The platinum metal chalcogenides in general are easier to prepare than the corresponding oxides. Whereas special conditions of temperature and pressure are required to prepare many of the oxides, the platinum metals react most readily with S, Se, and Te. A number of additional differences concerning the chemistry of the chalcogenides and the oxides are summarized as follows: The metal-sulfur (selenium, tellurium) bond has considerably more covalent character than the metal-oxygen bond and, therefore, there are important differences in the structure types of the compounds formed. Whereas there may be considerable similarity between oxides andfluorides,the structural chemistry of the sulfides tends to be more closely related to that of the chlorides. The latter compounds 17 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

18

P L A T I N U M

GROUP

M E T A L S

A N D

C O M P O U N D S

f o r m as p r i m a r i l y l a y e r - t y p e structures, a n d a n u m b e r of i m p o r t a n t s t r u c t u r e types are f o u n d i n sulfides that h a v e n o c o u n t e r p a r t a m o n g the o x i d e structures—e.g., p y r i t e , m a r c a s i t e , n i c k e l arsenide. F i n a l l y , m a n y of t h e p l a t i n u m m e t a l c h a l c o g e n i d e s b e h a v e l i k e a l l o y s ; t h e elements d o a p p e a r to h a v e t h e i r n o r m a l valencies a n d , i n a d d i t i o n , the

not

compounds

h a v e a w i d e r a n g e of c o m p o s i t i o n a n d s h o w m e t a l l i c luster, r e f l e c t i v i t y , and conductivity. Goodenough

(10)

has a c c o u n t e d for the m e t a l l i c p r o p e r t i e s of

a

n u m b e r of first r o w t r a n s i t i o n m e t a l c h a l c o g e n i d e s , a n d these ideas are also a p p l i c a b l e to the p l a t i n u m m e t a l chalcogenides.

H e has s h o w n that

t h e f o r m a t i o n of c o n d u c t i o n b a n d s is p o s s i b l e as a result of strong covalent m i x i n g between the cation e

9

a n d a n i o n s,p

a

orbitals. T h i s m i x i n g


a l l o w s sufficient i n t e r a c t i o n b e t w e e n o c t a h e d r a l l y c o o r d i n a t e d cations o n opposite sides of a n a n i o n so that the c o n d i t i o n s for l o c a l i z e d d-electrons break down.

T h e r e s u l t i n g d - l i k e c o l l e c t i v e - e l e c t r o n b a n d s , w h i c h are

a n t i b o n d i n g w i t h respect to the a n i o n array, are d e s i g n a t e d σ * b a n d s . M e t a l l i c b e h a v i o r c a n o c c u r w h e n these b a n d s exist a n d are p a r t i a l l y o c c u p i e d b y electrons. M e t a l l i c c o n d u c t i o n m a y o c c u r also i f c o n d u c t i o n b a n d s are f o r m e d b y the d i r e c t o v e r l a p of t r a n s i t i o n m e t a l t

2g

orbitals.

H e r e a g a i n , these b a n d s m u s t b e p a r t i a l l y o c c u p i e d .

et al. (19)

—

t

2g

Rogers

h a v e a p p l i e d the G o o d e n o u g h m o d e l to a c c o u n t for the elec

t r i c a l b e h a v i o r of a n u m b e r of p l a t i n u m m e t a l oxides.

T h e s e concepts

m a y also b e a p p l i e d to t h e p l a t i n u m m e t a l chalcogenides. It w i l l not b e possible, i n this p a p e r , to d e a l w i t h a l l of the p l a t i n u m m e t a l chalcogenides.

I n s t e a d , a n u m b e r of examples w i l l be c h o s e n a n d

t h e i r e l e c t r i c a l as w e l l as m a g n e t i c p r o p e r t i e s c o r r e l a t e d w i t h the a t o m i c positions i n the v a r i o u s structures f o r m e d . T h e first g r o u p of c o m p o u n d s to b e d i s c u s s e d c r y s t a l l i z e w i t h the p y r i t e structure, w h i c h is s h o w n i n F i g u r e 1.

T h i s s t r u c t u r e is s i m i l a r to the N a C l structure i f w e r e p l a c e

N a b y F e a n d each C I b y an S group. H o w e v e r , the S - S distance w i t h i n 2

R.

Figure 1.

W.

Pyrite structure

G. Wyckoff,

"Crystal Structures," Wiley

(20)


2.

Phtinum

W O L D

Table I.

Metal

19

Chalcogenides

Platinum Metal Compounds with the Pyrite Structure Compounds

Properties

Low Spin RuS , OsS , RhPS, RhPSe,

RuSe , OsSe , RhAsS, RhAsSe, RhAsTe, IrPS, IrAsS, IrPSe, IrAsSe, IrAsTe, N i o . P d o .eAsa, PtAs , PtP„ PtBi RhSe~ , RhS~ , IrS^ , IrSe^ IrTe~ 2

2

2

2

2

2

rf

S =

6

0 Semiconductor Semiconductor Semiconductor Semiconductor Semiconductor Semiconductor Semiconductor Semiconductor Metallic Semiconductor Metallic Semiconductor Semiconductor Metallic

RuTe OsTe RhSbS, RhBiS RhSbSe, RhBiSe RhSbTe, RhBiTe IrSbS, IrBiS IrSbSe, IrBiSe IrSbTe, IrBiTe PdAs , PdSb PtSb 2

2

2

2

2


2

3

3

3

RhTe~

3

3

3

3. 2

2n and k =

2n.

A y e l l o w - b r o w n c o m p o u n d , S r P d 0 , is f o r m e d w h e n t h e 2

3

a p p r o p r i a t e s t a r t i n g m i x t u r e ( i n p e l l e t f o r m ) is fired at 9 5 0 ° C i n a i r for


s e v e r a l days. T h e c o m p o u n d is t h e r m a l l y q u i t e stable, e v e n at 1 2 0 0 ° C . It dissolves r a p i d l y i n d i l u t e a c i d s , a n d w h e n b r o u g h t i n contact w a t e r , i t alters to a n u n i d e n t i f i e d h y d r a t e d p r o d u c t . the f o r m u l a .—Sri. Pdi. o0 . 93

0

w i t h χ as h i g h as 0.6.

3+a

an i d e a l f o r m u l a of S r P d 0 2

with

A n a l y s e s l e a d to W e have assumed

for reasons d i s c u s s e d b e l o w .

3

R o t a t i o n a n d W e i s s e n b e r g patterns w e r e t a k e n of a s i n g l e c r y s t a l of S r P d 0 . T h e s i n g l e - c r y s t a l d a t a l e a d to a b o d y - c e n t e r e d o r t h o r h o m b i c 2

3

u n i t c e l l . P o w d e r d a t a (a

=

Q

3.970A, b

=

Q

3.544A, c

0

=

1 2 . 8 4 A ) are i n

g o o d a g r e e m e n t w i t h the s i n g l e - c r y s t a l d a t a . T h e o n l y e x t i n c t i o n s f o u n d w e r e those f o r b o d y - c e n t e r i n g ; t h u s , the f o u r p o s s i b l e space g r o u p s a r e D

2 h

2 5

- J m m m , ό2*-Ι222,

ώ2 -Ι2 2 2 , 9

1

1

and c

1

2 v

2 0

-Irara2.

B o t h s y m m e t r y a n d u n i t c e l l constants are s i m i l a r to t h e c o r r e s p o n d i n g v a l u e s of K N i F 2

4

t y p e c o m p o u n d s , as is s h o w n i n T a b l e I I .

w e h a v e f o u n d t h a t a reasonable s t r u c t u r e c a n b e d e r i v e d for w h i c h is closely r e l a t e d to the K N i F 2

t u r e , t h e space g r o u p D

2 h

2 5

Indeed, Sr Pd0 2

3

s t r u c t u r e . I n this p r o p o s e d s t r u c

4

- Z r a r a r a is a s s u m e d a n d t h e atoms are p l a c e d

as f o l l o w s : 4 S r i n (4i) : OOz, OOF + 2 P d i n (2a) : 000 + 2 Ο i n (26)-: O H +

b.c. w i t h ζ =

0.355

b.c. w i t h ζ =

0.16

b.c. b.c.

4 Ο i n (4i) : 00z, OOz +

W i t h this a s s u m p t i o n , intensities for the p o w d e r p a t t e r n w e r e c a l c u l a t e d i n t h e same m a n n e r as d e s c r i b e d p r e v i o u s l y (8).

A l l tempera

t u r e coefficients w e r e a s s u m e d to b e zero. T h e c a l c u l a t e d intensities are l i s t e d i n T a b l e I I I a n d c o m p a r e q u i t e f a v o r a b l y w i t h the o b s e r v e d i n tensities. T h e i n t e n s i t y d i s c r e p a n c y f a c t o r R = w a s c a l c u l a t e d as 6.6.

100 ( 2 | I

0

—

I | c

h)

I n c a l c u l a t i n g the R - f a c t o r , t h e intensities w h i c h

w e r e too w e a k to b e o b s e r v e d w e r e a s s i g n e d J obs. v a l u e s of zero.


The

32

P L A T I N U M

Table II.

G R O U P

M E T A L S

Compound

a , A

Sr Ir0 Sr Rh0 Sr Ru0

4

2

4

3.89 3.85 3.870

3

3.970

2

b , A

0

2

4

Sr Pd0

Table III.

0

3.544

Co, A

Ref.

12.92 12.90 12.74

(12) (13) (13)

12.84

present work

Symmetry Space Group Structure Type Tetragonal K NiF 2

4

Orthorhombic

2

0

Space group:

=

Q

D

2 2

h

5

—

Immm;

3.544A, a n d c

Q

=

12.84A

n.o. = n o t o b s e r v e d .

d obs., A

d cale, A

I obs.

I calc.

hkl

6.44 n.o. 3.419 3.217 2.912 2.730 2.643 2.447

6.42 3.793 3.416 3.210 2.911 2.730 2.644 2.445

10.2 n.o. 3.2 2.6 64.0 73.9 100.0 1.8

22.4 0.1 3.3 2.4 67.6 76.2 98.9 2.2 J 10.2 \22.2 14.0 6.4 25.2 1.9 17.2 / 0.6

002 101 011 004 103 013 110 112 105 006 015 114 200 202 020 211 022 204 107 116 017 213 008 024 123 206 215 118 125 026 109 019 220

2.141

g;}»

33.3

2.079 2.041 1.985 1.896 1.772 1 711 '

2.079 2.041 1.985 1.896 1.772 fl-716 \1.708 1.688 1.665 [1.663 1.629

12.8 6.4 25.8 1.5 18.9

1

/

1.663 n.o.

1.605

n.o. 1.513 1.455 1.436 1.368 1.342 1.322

structure

X - R a y Diffraction Powder D a t a for S r P d 0

O r t h o r h o m b i c : a — 3.970A, b Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

C O M P O U N D S

Structural D a t a for Some Strontium-Noble Metal Oxides Unit Cell Constants

2

A N D

1

7

1A

35.2 n.o.

{;5jg 36.8 :

1.551 1.514 1.455 1.436 (1.372 1.369 [1.365 1.343

{}fg

1 0.6

n.o. 20.4 14.3 6.2

21.8 2.9 14.7

0.9 [30.3 0.2 /30.0

1 0.4 5.1 19.7 11.8 7.8 f 9.2 4.6 [ 9.3 2.2 / 3.0 112.2


3

3.

M U L L E R

A N D

New

R O Y

Palladium

Table III.

33

Oxides

(Continued)

O r t h o r h o m b i c : a = 3.970A, b — 3.544A, a n d c = 0

Q

Space g r o u p :

2 2

5

h

—

Immm;

n.o.

12.84A

not observed.

d cale, A

I obs.

I calc.

hkl

1.295 1.284

n.o. n.o.

1.264

j}| a n d C d o . 5 P d . o o 0 . . T h e s t r o n t i u m 3

4

3

4

9

3

4

03

c o m p o u n d gives h i g h e r t h a n e x p e c t e d o x y g e n contents, e s p e c i a l l y w h e n the samples are p r e p a r e d at h i g h o x y g e n pressures.


36

P L A T I N U M

T h e x - r a y p o w d e r d a t a for S r P d 0 3

4

GROUP

M E T A L S

A N D

C O M P O U N D S

are g i v e n i n T a b l e I V . C a P d 0 3

4

a n d C d P d 0 g i v e v e r y s i m i l a r p o w d e r patterns. A l l three patterns c a n b e 3

4

i n d e x e d o n t h e basis of a p r i m i t i v e c u b i c u n i t c e l l w i t h c e l l constants of 5.826, 5.747, a n d 5.742A for S r P d 0 , C a P d 0 , a n d C d P d 0 , respec 3

4

3

4

3

4

t i v e l y . I n t e n s i t y c a l c u l a t i o n s w e r e c a r r i e d out i n a s i m i l a r m a n n e r as for S r P d 0 , a s s u m i n g the N a P t 0 2

3

x

3

4

structure (22,

p l a c e d as f o l l o w s i n space g r o u p

T h e atoms

23).

were

o -Pm3n: 3

h

2 S r ( C a or C d ) i n (2a) : (ΟΟΟ,ΗΙ) 6 P d i n (6c) : ±

(10*, O )


8 Ο i n (8e) : ± (ΙΗ,ΗΪΟ) Table V .

Structural D a t a for Compounds with the N a P t 0 x

Cubic, S.G.: o

h

Interatomic

3

-

3

4

Structure

Pm3n

Distances,

A

a

Composition

a, A

Pt-0 or Pd-O, square planar

Pt 0 Mg Pt 0 Na Pt 0

5.585 5.621 5.69

1.974 1.987 2.01

2.418 2.434 2.46

2.792 2.810 2.84

(7) (ID (22,23)

5.64 5.742 5.747 5.826

1.99 2.030 2.032 2.059

2.44 2.486 2.488 2.523

2.82 2.871 2.873 2.913

(16) Present work Present work Present work

3

4

x

3

x

3

Na Pd 0 CdPd 0 CaPd 0 SrPd 0 x

3

3

4

4

4

3

3

4

4

4

0

Me-O, 8-fold, cubic

Shortest, Pt-Pt or Pd-Pd

Reference

The interatomic distances for C d P d s O * , CaPd C>4, and S r P d 0 4 are believed to be accurate to within db 0.002A. This small error is a function only of the accuracy of the do cell edge measurements, since there are no variable positional parameters in the a

3

3

N a x P t 0 * structure. 3

T a b l e I V shows t h a t the i n t e n s i t y a g r e e m e n t is q u i t e g o o d . i n t e n s i t y d i s c r e p a n c y factors R =

100 (%\I

The

— 7 |)/2(J ) were calcu

Q

C

0

l a t e d as 5.8, 7.8, a n d 8.4 for S r P d 0 , C a P d 0 , a n d C d P d 0 , respec 3

tively.

4

3

4

3

4

I n T a b l e V , the i n t e r a t o m i c distances for these c o m p o u n d s

c o m p a r e d w i t h the distances f o u n d for other N a P t 0 - t y p e phases. x

s q u a r e p l a n a r P d - O b o n d lengths a n d t h e c u b i c Sr-O,

3

4

are The

(eight-coordinated)

C a - O , a n d C d - O distances are i n g o o d agreement w i t h the ex

p e c t e d values. S q u a r e p l a n a r c o o r d i n a t i o n is c o m m o n for d i v a l e n t p a l l a d i u m c o m p o u n d s , a n d the e i g h t - f o l d ( c u b i c ) e n v i r o n m e n t for S r , C a , 2 +

and C d

2 +

2 +

is e x p e c t e d f o r these ions. T h e r e l a t i v e l y short P d - P d distances

m a y i n d i c a t e the presence of some i n t e r - m e t a l l i c b o n d i n g . I n these c o m -


3. MULLER AND ROY

New Palladium Oxides

37

pounds, the palladium atoms are apparently completely ordered in the (6c) sites. We have found no x-ray evidence for any noticeable disorder between the two different cations in CaPd 0 . Because of the strong preference of Pd for square planar coordination, it can be assumed that no such disorder exists in SrPd 0 and CdPd 0 , although this could not be proved easily by x-ray methods since the atomic scattering factors for Sr, Cd, and Pd are very similar. Mg Pd0 . When Mg(OH) -Pd black mixtures are heated at high oxygen pressures—e.g., at 900 °C and 200 atm of oxygen—a poorly crystallized spinel phase is formed with a = 8.501A. We have not yet succeeded in preparing this spinel in a pure state, since this phase is always accompanied by some unreacted MgO and PdO. From crystal-chemical considerations and from the x-ray intensities, we have tentatively assigned the stoichiometry Mg Pd0 to this phase. Mg Pd0 is apparently an inverse spinel with Pd occupying octahedral sites. The unit cell constant for Mg Pd0 , a = 8.501A, is slightly smaller than the corresponding value for Mg Pt0 , a = 8.521 A (10), owing to the slightly smaller ionic radius for Pd (17). 3

4

2+

3

2

4

4

3

4

2


0

2 4+

2

4

4

2

4

0

2 4+

4

0

Acknowledgment We thank W. A. Jester for the neutron activation analyses. This work was supported by the Advanced Research Projects Agency, Contract No. DA-49-083 OSA-3140, and by the U. S. Army Electronics Command, Contract DA28-043 AMC-01304 (E). Literature Cited (1) Guiot, J. M., J. Appl. Phys. 1968, 39, 3509. (2) Hoekstra, Henry R., Siegel, Stanley, Gallagher, Francis X., ADVAN. CHEM. SER. 1970, 98, 39. (3) McDaniel, C. M., Schneider, S. J.,J.Res. Natl. Bur. Std. 1968, 72A, 27. (4) Moore, W. J., Pauling, L,J.Am. Chem. Soc. 1941, 63, 1392. (5) Muller, O., Roy, R., Am. Ceram. Soc.Bull.1967, 46, 881. (6) Muller, O., Roy, R.,J.Inorg.Nucl.Chem. 1969, 31, 2966. (7) Muller, O., Roy, R.,J.Less-Common Metals 1968, 16, 129. (8) Ibid., 1969, 19, 209. (9) Ibid., 1970, 20, 161. (10) Muller, O., Roy, R., Mater. Res. Bull. 1969, 4, 39. (11) Muller, O., Roy, R., unpublished data. (12) Randall, J. J., Katz, L., Ward, R.,J.Am. Chem. Soc. 1957, 79, 266. (13) Randall, J. J., Ward, R.,J.Am. Chem. Soc. 1959, 81, 2629. (14) Sabrowsky, H., Hoppe, R., Naturwissenschaften 1966, 53, 501. (15) Scheer, J. J., Dissertation, Leiden, Netherlands, 1956. (16) Scheer, J. J., van Arkel, A. E., Heyding, R. D., Can. J. Chem. 1955, 33, 683.


38

PLATINUM GROUP METALS AND COMPOUNDS

Shannon, R. D., Prewitt, C. T., Acta Cryst. 1969, B25, 925. Shannon, R. D., Rogers, D. B., Prewitt, C. T., in press. Sleight, A. W., Mater. Res. Bull. 1968, 3, 699. Teske, C. L., Muller-Buschbaum, H., Z. Anorg. Allgem. Chem. 1969, 371, 325. Waser, J., Levy, Η. Α., Peterson, S. W., Acta Cryst. 1953, 6, 661. Waser, J., McClanahan, E. D.,J.Chem. Phys. 1951, 19, 199. Ibid., 1951, 19, 413. RECEIVED February 2, 1970.


(17) (18) (19) (20) (21) (22) (23)


4

Reaction of Platinum Dioxide with Some Metal Oxides

HENRY R. HOEKSTRA, STANLEY SIEGEL, and FRANCIS X. GALLAGHER


Argonne National Laboratory, Argonne, Ill. 60439 The structure of platinum dioxide and its reactions with some di, tri, and tetravalent metal oxides have been investigated. Ternary platinum oxides were synthesized at high pressure (40 kilobars) and temperature (to 1600°C). Properties of the systems were studied by x-ray, thermal analysis, and infrared methods. Complete miscibility is observed in most PtO -rutile-type oxide systems, but no miscibility or compound formation is found with fluorite dioxides. Lead dioxide reacts with PtO to form cubic Pb Pt O . Several corundum-type sesquioxides exhibit measurable solubility in PtO . Two series of compounds are formed with metal monoxides: M PtO (where M is Mg, Zn, Cd) and MPt O (where M is Mg, Co, Ni, Cu, Zn, Cd, and Hg). 2

2

2

2

7

2

2

4

3

6

'Tphe literature on anhydrous binary or ternary platinum oxides is relatively limited. Muller and Roy (6) have reviewed the simple platinum oxides and were able to confirm the existence of only two oxides, P t 0 and Pt0 , with the dioxide existing in two crystal modifications. Shannon (13) has discussed the preparation and properties of orthorhombic Pt0 . Ternary oxides of platinum include several with the alkali metals (NaJPtsO^ Na Pt0 , L i P t 0 ) (12) and with the alkaline earths [Ba Pt 0 (18), Sr Pt 0 , and Sr PtO (10)]. More recent work has been reported on T l P t 0 (4) and the rare earth-platinum pyrochlores (3, 17), as well as the spinels Z n P t 0 and M g P t 0 (5). The investigations of platinum pyrochlores have demonstrated the effectiveness of high pressure techniques in the synthesis of anhydrous oxides when one or both reactants have limited thermal stability. The bulk of the work reported here represents a continuation of an exploration of metal oxide-platinum oxide systems at high pressure. 3

4

2

2

2

3

2

7

3

3

2

7

2

2

7

2

3

4

2

e

4

2

4


40

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

Equipment and Procedure T h e h i g h pressure a p p a r a t u s u s e d i n this w o r k is a t e t r a h e d r a l a n v i l apparatus. D e t a i l s of the e q u i p m e n t , the o p e r a t i n g p r o c e d u r e , a n d the sample assembly have been described previously (2) r e p e a t e d here.

B r i e f l y , the p o w d e r e d

and w i l l not

be

o x i d e samples are w r a p p e d i n

p l a t i n u m or i n g o l d f o i l to isolate t h e m , as m u c h as possible, f r o m r e a c t i o n w i t h m a t e r i a l s other t h a n the reactant m i x t u r e . W e s h a l l see t h a t o n occasion the o x i d e samples w i l l react w i t h the p l a t i n u m f o i l c o n t a i n e r to g i v e l o w e r v a l e n c e p l a t i n u m oxides. A s a r u l e , three o x i d e samples, w h i c h h a v e b e e n w r a p p e d i n f o i l a n d pressed i n t o pellets, are l o a d e d i n t o the s a m p l e c a v i t y (•—1

cc v o l u m e ) of a p y r o p h y l l i t e t e t r a h e d r o n for e a c h


h i g h pressure r u n . I n a t y p i c a l e x p e r i m e n t , the t e t r a h e d r o n w i t h its three samples is c o m pressed to 40 k b pressure; the s a m p l e c a v i t y is h e a t e d to 1200 ° C a n d m a i n t a i n e d at that t e m p e r a t u r e for a n h o u r b e f o r e b e i n g q u e n c h e d room temperature.

F i n a l l y , pressure is released s l o w l y .

to

A l t h o u g h the

b u l k of o u r experiments h a v e b e e n r u n at 40 k b pressure, the range i n pressure a p p l i e d has v a r i e d f r o m 20 to 60 k b ; e x p e r i m e n t a l temperatures v a r i e d f r o m 500° to 1600 ° C . W e find that u n d e r these e x p e r i m e n t a l c o n d i t i o n s loss of a n a p p r e c i a b l e a m o u n t of o x y g e n f r o m the s a m p l e p e l l e t occurs v e r y r a r e l y , e v e n t h o u g h the oxides are h e a t e d to several h u n d r e d degrees a b o v e t h e i r d e c o m p o s i t i o n t e m p e r a t u r e at a t m o s p h e r i c pressure.

E x c e p t i o n s to this

r u l e o c c u r w i t h the f o r m a t i o n of a n y stable oxide phase w h i c h does not u t i l i z e a l l of the oxygen present i n the i n i t i a l reactant m i x t u r e . T h i s "excess" o x y g e n is lost r a t h e r r a p i d l y f r o m the s a m p l e enclosure. O u r i n v e s t i g a t i o n of the properties of the p l a t i n u m oxides i n c l u d e s x-ray, i n f r a r e d , a n d t h e r m a l analysis. P o w d e r x - r a y d a t a w e r e o b t a i n e d w i t h a P h i l i p s 114.59 m m c a m e r a , u s i n g either N i - f i l t e r e d C u r a d i a t i o n or V - f i l t e r e d C r r a d i a t i o n . C e l l parameters w e r e o b t a i n e d u s i n g a least squares refinement, a n d are b a s e d o n C u Κα = 2.2909. T h e dta-tga

1.5418 A a n d C r Κα —-

results w e r e o b t a i n e d o n a M e t t l e r r e c o r d i n g t h e r m o -

a n a l y z e r over the t e m p e r a t u r e i n t e r v a l 2 5 ° - 1 4 0 0 ° C , w i t h a h e a t i n g rate of 6 ° / m i n u t e a n d a s e n s i t i v i t y of 100 μΥ.

I n f r a r e d spectra to 200 c m "

w e r e t a k e n w i t h a B e c k m a n I R - 1 2 spectrophotometer.

1

N u j o l mulls were

s p r e a d o n p o l y e t h y l e n e disks for the l o w f r e q u e n c y p o r t i o n of the spec t r u m a n d o n K B r plates for the frequencies a b o v e 400 c m " .

Platinum

1

d i o x i d e w a s p r e p a r e d b y the r e a c t i o n of K P t C l 2

purity) with molten K N 0 s o l u t i o n of the K N 0 for several hours. than 0.2%

3

3

at 4 0 0 ° C .

4

or K P t C l 2

6

(99.9%

T h e dioxide was recovered

by

i n water and purified by heating i n aqua regia

S p e c t r o c h e m i c a l analysis of the p r o d u c t s h o w e d less

of a l k a l i metals, a n d no w a t e r or h y d r o x y l i o n w a s


detect-

4.

H O E K S T R A

E T

Reaction

A L .

Table I.


41

Dioxide

X - r a y Powder Data for a - P t 0 a = 3.100(2)

Hexagonal

a

of Platinum

hkl

d

001 100 101 002 102 110 111 003 200 201 112 103 202 113 210 211 203 212 300 301 114 302

4.107 2.664 2.241 2.065 1.637 1.543 1.448 1.381 1.337 1.2734 1.2388 1.2287 1.1255 1.0309 1.0126 0.9841 0.9628 0.9111 0.8945 0.8752 0.8629 0.8218

c = 4.161(3)

2

A

I calcd

I obsd

a

100 100 170 15 100 50 70 10 25 50 40 50 50 40 40 90 45 115 30 60 80 75

60 100 90 10 60 90 70 1 45 50 30 15 35 5 55 55 20 60 35 40 20 100

Based on C d l - t y p e structure. 2

able b y i n f r a r e d analysis. M e t a l oxides u s e d i n the reactions w i t h P t 0

2

w e r e u s u a l l y reagent grade c h e m i c a l s ; exceptions i n c l u d e d oxides s u c h as F e O , C r 0 , M n O , M n 0 , V 0 , a n d M o 0 , w h i c h w e r e p r e p a r e d b y 2

accepted

2

procedures

3

2

2

f r o m reagent grade s t a r t i n g m a t e r i a l s . P u r i t y

of

these p r o d u c t s w a s c o n f i r m e d b y x-ray, t h e r m a l , a n d c h e m i c a l analysis.

Results «-Pt0 . 2

S e v e r a l proposals c o n c e r n i n g t h e structure of the a m b i e n t

pressure f o r m of P t 0

2

h a v e b e e n r e v i e w e d b y M u l l e r a n d R o y (6).

Diffi-

culties arise p r i n c i p a l l y f r o m the p o o r c r y s t a l l i n i t y w h i c h characterizes this phase, regardless of the h e a t i n g t i m e e m p l o y e d i n its p r e p a r a t i o n . D i s o r d e r is p a r t i c u l a r l y t r o u b l e s o m e i n the o d i r e e t i o n of the h e x a g o n a l structure since hkl lines w i t h 1 ^ 0

b e c o m e i n c r e a s i n g l y w e a k a n d diffuse

w i t h increase i n 1. O u r experience w i t h the synthesis of [Os N(NH ) X J X 100°C,Carius (X = Cl,Br) tube

2

[Os NCl (H 0) ] 8

2

[Os N(NH ) 2


G R O U P

3

3

2

2

8

3

Aq.

3

> [Os N(NH ) 100°C, C a r i u s tube

Cl ] +

8

3

3

2

3

Excess X ~ > [Os N(NH ) Reflux i n a q . soin 2

3

C1 ]C1

8

2

3

X ] +

8

2

3

(X = Br,I,NCS,N ,N0 ) 3

[Ru N(NH ) 2

NH [Ru N 2

3

3

3

C1 ]C1

8

2

2

Aq.

X (H 0) ] ~ 8

2

2

3

Heat [Ru N(NH ) (H 0)Cl ]Cl 2

Figure

1.

Structure

of the anion in

3

6

2

3

2

K [Ru NCl (HgO) ] 3

2

8

2

= N " , N C S " , N 0 " ) . I t appears t h a t other ligands—e.g., N 0 " — w i l l l e a v e t h e c o m p o u n d as a n o c t a m m i n e . Species of t h e t y p e [ R u N ( N H ) ( H 0 ) Y ] Z m a y b e m a d e b y metathesis w i t h Z " i n t h e c o l d ( Z = C 1 , I ) . 3

2

3

2

2

3

2


3

6

5.

C L E A R E

E T

Nitrido

A L .

59

Complexes

M o l a r c o n d u c t a n c e s for the o s m i u m a n d r u t h e n i u m o c t a m m i n e s i n aqueous s o l u t i o n w e r e close to the values e x p e c t e d f o r 3:1 (.—360 m h o s c m )

electrolytes

b u t rose o n s t a n d i n g or h e a t i n g to g i v e final values

2

nearer that e x p e c t e d for a 5:1 electrolyte ( ^ 6 0 0 m h o s c m ) .

T h i s is p r e

2

s u m a b l y because of trans a q u a t i o n ; the effect w a s a g a i n less m a r k e d for o s m i u m . S i g n i f i c a n t l y , a l l the h a l o g e n i n the h a l o species [ R u N ( N H ) 2

3

Χ 2 ] Χ δ c o u l d be p r e c i p i t a t e d w i t h silver n i t r a t e f r o m h e a t e d

8

solutions.

C o n d u c t i v i t i e s for the h e x a m m i n e s also v a r i e d s o m e w h a t w i t h t i m e , b u t i n i t i a l values w e r e l o w e r t h a n for the o c t a m m i n e s presence of a 2:1 electrolyte (240 m h o s c m )

and indicated

the

(5)

2

A n x-ray s t r u c t u r a l d e t e r m i n a t i o n has b e e n c a r r i e d out

Structure.

on K [ R u 2 N C l ( H 0 ) 2 ] 3

8

(3)

2

a n d the results are d e p i c t e d i n F i g u r e 1.


T h e a n i o n has a l i n e a r skeleton w i t h the e i g h t e q u a t o r i a l c h l o r i n e atoms e c l i p s e d so that the o v e r - a l l i d e a l i z e d s y m m e t r y of the a n i o n is D .

Each

4h

r u t h e n i u m a t o m is d i s p l a c e d 0.19 A out of the C l n i t r o g e n atom.

4

plane toward

the

S u c h a d i s p l a c e m e n t of m e t a l atoms t o w a r d s a 7r-donor

l i g a n d has b e e n o b s e r v e d i n other complexes, s u c h as K [ R e O C l i ] 4

2

(18)

0

a n d (Ph^As) [ M o O B r H 0 ] ( 7 ) , as w e l l as K [ O s N C l ] ( I ) , w h i c h has 4

2

2

5

b e e n m e n t i o n e d p r e v i o u s l y . I t has b e e n suggested that this arises m a i n l y f r o m the r e p u l s i o n b e t w e e n the n i t r o g e n a n d c h l o r i n e l i g a n d s w i t h i n t h e molecule. S p e c t r a of

Vibrational Spectra.

t y p i c a l complexes are l i s t e d i n

T a b l e s V a n d V I . T h e c o m p o u n d s e x h i b i t s i m i l a r spectra,

suggesting

that t h e y a l l h a v e the same b a s i c structure. T h e m a i n features a r e : ( a ) T h e presence of a strong sharp b a n d i n the i n f r a r e d i n the r a n g e 1 0 5 0 - 1 1 3 0 c m " , not o b s e r v e d i n t h e R a m a n . T h i s b a n d is l i t t l e c h a n g e d i n f r e q u e n c y o n d e u t e r i a t i o n , b u t shifts d o w n w a r d b y s o m e 30 c m " o n 1

1

Table V .

Vibrational Spectra of Bridging Nitrido Complexes—Anionic Species

(M NX (H 0) y2

s

K (Os N 3

2

VM N

2

2

C1 (H 0) )

2

8

2

R

2

aS

—

2

8

267(10)

J315(4) /295(2) 303s b r

185w

329(4)

J301(10) (294(4)

200w

I R 1137 v s ° I R 1135 v s K (Ru N 3

C1 (H 0) )

2

8

2

R

2

—

R — I R 1078 v s a

a

K (Ru 3

a

2

1 5

N

C1 (H 0) ) 8

2

2

%X-M-X

V MN

330(4)p (315s /289m

I R 1080 v s I R 1046 vs

—

{315s /289m

Indicates aqueous solution measurement.


60

P L A T I N U M

Table V I .

3 s

2

3

2

2

8

3

(Os N(ND ) C1 )C1 2

3

2

8

3

(Ru N(NH ) C1 )C1 2

3

2

8

a

R — I R 1104 v s

299(10)

2

3

R — I R 1101 v s

286(10)

8

3

267(1) 260s b r

286(3) 282m

430w 440w

254(1) 240s b r

278m 281m

J496(3) 1475(1) 465w

265w b r

280w

258m br

2 8 0 m sh

440vw 430w

250(1) 245s b r

273w 2 7 7 m sh

— 354(1)

R

—

IR

1055

—

R — I R 1054 v s

339(10)


2

C O M P O U N D S

455w 465w

—

3

(Ru N(ND ) C1 )C1

A N D

%M—NH

VM-NH

VM N *

2

(Os N(NH ) C1 )C1

M E T A L S

Vibrational Spectra of Bridging N i t r i d o Complexes—Cationic Species

(M N(NH ) X y+ 2

GROUP

—

Figure 2. Bonding in Ο—Ru and Ru—Ν—Ru tems

Ru— sys

Diagram shows 4 d « - 2 p - 4 c L overlap. There will be a sim ilar 4 d x y - 2 p y - 4 d x y ΟΌβ^Ρ ΰ ί right angles to the plane of the paper. e

B

—

-4d =4d

x

z

y 2

EMPTY PAIRED METAL ELECTRONS PAIRED LIGAND ELECTRONS

•U

Figure

3.

Bonding

in bridging

nitride

complexes

The M.O. diagram indicates the formation of two sets of 3-center molecular orbitals with the metal d electrons paired in the nonbonding orbitals

N substitution i n [ O s N ( N H ) B r ] B r and K [ R u NCl (H 0) ]. T h i s b a n d w e h a v e assigned to v M N> the a s y m m e t r i c M — Ν — M stretch. T h i s m o d e consists almost e n t i r e l y of n i t r o g e n m o v e m e n t a n d is expected to o c c u r i n the same r e g i o n as t h e t e r m i n a l m e t a l n i t r i d e stretches. ( b ) T h e presence of a s t r o n g , s h a r p , p o l a r i z e d R a m a n b a n d near 350 c m " f o r the r u t h e n i u m complexes a n d 280 c m " for the o s m i u m c o m 1 5

2

1 5

1 5

3

as

1

8

2

3

3

2

1 5

8

2

1


2

2

5.

C L E A R E

E T

Nitrido

A L .

61

Complexes

plexes, w h i c h w e assign to t h e s y m m e t r i c M — Ν — M s t r e t c h , V M N - T h e s e bands are n o t o b s e r v e d i n t h e i n f r a r e d spectra. T h e y shift d o w n w a r d some 13 c m " o n d e u t e r i a t i o n of t h e a m m i n e complexes, b u t this is l i k e l y to b e c a u s e d b y strong c o u p l i n g of V N ( a totally symmetric m o d e ) w i t h the s y m m e t r i c m e t a l a m m i n e stretches a n d deformations h a v i n g t h e same s y m m e t r y species (A ), together w i t h a slight effect a r i s i n g f r o m t h e greater mass of d e u t e r i u m . H e r e t h e m o d e consists m a i n l y of m e t a l m o v e m e n t ; this is c l e a r l y s h o w n b y t h e effect of t h e extra mass of o s m i u m . T h e g e n e r a l l a c k of c o i n c i d e n c e b e t w e e n R a m a n a n d i n f r a r e d bands a n d , i n p a r t i c u l a r , t h e fact that t h e R a m a n - a c t i v e V M N a n d i n f r a r e d - a c t i v e v M N a r e i n a c t i v e i n the i n f r a r e d a n d R a m a n , respectively, strongly s u g gest t h e presence of a center of s y m m e t r y . T h u s , as i n [ R u N C l ( H 0 ) 2 ] ~ t h e a q u o groups l i e trans to the n i t r i d e g r o u p , i t is l i k e l y t h a t the X groups i n [ M N ( N H ) X ] w i l l b e p l a c e d s i m i l a r l y ( 5 ) . S

2

1

S

M

2

lg

S

as

2

2

2

8

3

2


2

3

8

2

3 +

E l e c t r o n i c S p e c t r a . A l l these complexes are d i a m a g n e t i c as a result of t h e 7r-bonding, w h i c h is s h o w n i n F i g u r e 2. O f t h e f o u r m e t a l d electrons o n e a c h r u t h e n i u m a t o m ( R u ( I V ) d ) , t w o {d ,d ) w i l l p a i r u p i n t h e n o n b o n d i n g m o l e c u l a r o r b i t a l of t h e set p r o d u c e d b y t h e 3-center o v e r l a p b e t w e e n t h e d a n d d orbitals o n e a c h m e t a l a t o m , a n d t h e 2p a n d 2p orbitals o n t h e n i t r i d e . T h e l o w e r energy n i t r i d e electrons w i l l p a i r i n the b o n d i n g m o l e c u l a r orbitals ( F i g ure 3 ) . T h e r e m a i n i n g t w o electrons p e r r u t h e n i u m a t o m are p a i r e d i n t h e 4 dy o r b i t a l w h i c h remains essentially n o n b o n d i n g . I t is a consequence of this b o n d i n g scheme that t h e M — Ν — M g r o u p s h o u l d b e l i n e a r a n d that t h e e q u a t o r i a l ligands s h o u l d b e i n t h e e c l i p s e d (D ) rather than the staggered ( D ) positions. 4

xy

xz

xy

y

xz

z

Z

4h

4 d

Figure

4.

Electronic

spectra of some bridging complexes

nitrido


62

P L A T I N U M

G R O U P

5 0 s 0 + 7NH (llq) I l ^ L ^ 4

M E T A L S

A N D

C O M P O U N D S

Os N 0 H |

3

3

7

9

2

ORIGINAL FORMULATION HN 3

\/

OH

HO

—Os

/\

IR. BANDS

HN


NH

\/

3

= O s = 0

/\

OH

2

OH

NH

3

AT 1087, 1025, 970cm SHIFT

1053,997, 935cm

NEW

Ν

/\

OH

3

HO

\/

0 = O s = N HN

OH

, 5

ON

N

TO

SUBSTITUTION

FORMULATION HO

OH

v

\/

H O — Os = H^N

Figure

H^l

\/

HOI

Ν — Os

\>H

5.

OH

\/

Ν =

N^^NH

3

Os

HO^

NH

3

OH ^OH

Trinuclear Os(VI) nitndo plex

com

T h e electronic spectra (350-190 τημ) of three of these complexes are s h o w n i n F i g u r e 4. Jorgensen a n d O r g e l (14)

h a v e suggested that s i m i l a r

bands observed i n K [ R u O C l i ] arise f r o m transitions f r o m the h a l o g e n 4

2

0

l i g a n d s to the a n t i b o n d i n g m o l e c u l a r o r b i t a l f r o m the 3-center b o n d . f o l l o w this assignment for the

[M NX Y2]

system, a l t h o u g h i t is n o t

8

2

We

s t r i c t l y isolectronic w i t h [ R u O X i ] " . T h e R u — O — R u a n d R u — N — R u 2

groupings

are, h o w e v e r ,

4

0

isolectronic.

The

energy

of t h e a n t i b o n d i n g

m o l e c u l a r o r b i t a l is d e t e r m i n e d l a r g e l y b y the extent of the R u — Ο — R u or R u — Ν — R u π-bonding.

T h e b a n d s are seen near 400 τημ for

O C l i o ] " a n d at 397 a n d 330 m ^ ^ ^ H ) [ O s O C l i o ] . 4

4

2

are h i g h e r i n energy (e.g., K [ O s N C l ( H 0 ) ] , 273 τημ; 3

( H 0 ) ] , 294 τημ), 2

2

2

8

2

[Ru 2

In nitride they

2

2

K [Ru NCl 3

2

8

i n d i c a t i n g that M - N ττ-bonding is stronger t h a n for

M - O i n these b i n u c l e a r systems.

Trinuclear Osmium Complex T h e final p r o d u c t of the r e a c t i o n of l i q u i d a m m o n i a w i t h O s 0 the e m p i r i c a l f o r m u l a O s N 0 H i (17,20). 3

r e d s p e c t r u m of the

15

7

9

2

4

has

W e h a v e s t u d i e d the i n f r a

N - s u b s t i t u t e d c o m p o u n d a n d p r o p o s e structure I I

( F i g u r e 5) rather t h a n structure I, w h i c h was suggested o r i g i n a l l y . B a n d s at 1087, 1025, a n d 970 c m " shift to 1053, 997, a n d 935 o n N - s u b s t i t u t i o n 1

15


5.

C L E A R E

E T

Nitrido

A L .

63

Complexes

a n d m a y b e assigned to O s — Ν — O s o r O s — Ν s t r e t c h i n g modes. T h e n e w f o r m u l a t i o n accounts f o r t h e o b s e r v a t i o n t h a t o n l y t w o molecules of a m m o n i a are released o n h e a t i n g w i t h a l k a l i , since t w o of the a m m i n e groups are i n a different e n v i r o n m e n t f r o m the other t w o (5), a n d thus p r e s u m a b l y h a v e different stabilities i n respect to m e t a l - n i t r o g e n b o n d strengths.

Trinuclear Iridium Complexes T h e reaction of ( N H ) [ I r C l ] w i t h b o i l i n g sulfuric acid yields a s o l u t i o n f r o m w h i c h green salts o f the f o r m M [ I r N ( S 0 ) e ( H 2 0 ) 3 ] c a n be p r e c i p i t a t e d ( 8 , J 5 ) . I t has b e e n suggested that t h e a n i o n has t h e structure s h o w n o n F i g u r e 6 w i t h a c o p l a n a r I r N u n i t a n d ττ-bonding b e t w e e n t h e 2 p o r b i t a l ( p e r p e n d i c u l a r to t h e I r N t r i a n g l e ) a n d t h e i r i d i u m atoms ( 1 3 , 19). T h e o x i d i z i n g p o w e r o f the species is consistent w i t h it's c o n t a i n i n g o n e I r ( I I I ) a n d t w o I r ( I V ) atoms p e r m o l e c u l e (8, 13). R e d u c t i o n w i t h v a n a d o u s i o n gives a s t r a w - y e l l o w species c o n t a i n i n g three I r ( I I I ) atoms p e r m o l e c u l e . X - r a y studies o n the s o m e w h a t s i m i l a r [ C r 3 0 ( C H C O O ) ( H 2 0 ) ] C l · 5 H 2 0 h a v e s h o w n that t h e C r O u n i t is p l a n a r w i t h a t r i a n g u l a r a r r a n g e m e n t of m e t a l atoms ( 9 ) . 4

3

6

4

3

4

3


z

3

3

6

3

s

m

Figure 6. Proposed struc ture for indium trinuclear nitrides The Ir N unit is believed to be coplanar with the iridium atoms at the corners of an equilateral triangle. A related structure has been found for [Cr 0(Aces

3

Table VII.

Trinuclear Iridium Nitrido Complexes H

S0

2

3(NH ) [Ir Cl ] 4

3

4

> (NH )4[Ir3N(S0 )6(H 0)3]

6

4

2

4

H 0 2

[Ir N(S0 ) (H 0) ] 3

4

6

2

4

3

[Ir N(S0 ) (H 0) ] ~ 3

4

6

2

3

KOH > K [Ir N(S0 ) (OH) ] Cold 7

3

4

Caustic alkali

6

Ir N(OH)

4

3

3

u

· nH 0 2

Boiling / HC1 + C s CI Cs [Ir NCl (H 0) ] 4

3

1 2

2

3


64

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

O t h e r reactions of [ I r a N i S O ^ e i H k O ^ ] " are s h o w n o n T a b l e V I I . 4

Cold

c a u s t i c a l k a l i e s react to r e p l a c e

the a q u o g r o u p s ,

giving

[Ir 3

N ( S 0 ) 6 ( O H ) ] " , w h i l e h o t a l k a l i appears to r e p l a c e t h e sulfate l i g a n d s 7

3

4

to g i v e

a hydroxy

precipitate w h i c h probably

Ir N(OH)u · nH 0. 3

m a y be

described

as

T h e I r N g r o u p is s t i l l i n t a c t as r e a c t i o n w i t h s u l -

2

3

f u r i c a c i d regenerates the o r i g i n a l c o m p l e x .

The hydroxy complex

dis-

solves i n H C 1 to g i v e a species w h i c h appears to b e [ I r N C l i ( H 0 ) ] ~ . 3

2

2

3

4

W e h a v e m e a s u r e d t h e i n f r a r e d s p e c t r a of these species c o n t a i n i n g both

N and

1 4

N , a n d i n e a c h case a b a n d n e a r 780 c m " shifts d o w n w a r d

1 5

1

i n f r e q u e n c y b y some 20 c m "

1

on

to t h e a s y m m e t r i c I r N s t r e t c h . 3

1

5

N s u b s t i t u t i o n . W e assign this b a n d

T h e R a m a n s p e c t r a of the c o m p l e x e s

w e r e p o o r , o w i n g to t h e i r u n f a v o r a b l e colors, b u t w e a k b a n d s n e a r 230


cm"

m a y b e c a u s e d b y t h e s y m m e t r i c I r N stretch ( 5 ) .

1

3

s p l i t t i n g of the sulfate m o d e s is s i m i l a r to that o b s e r v e d ( S 0 ) ] (10), 4

S0

4

The

complex

in K i [ I r O 0

3

a n d p r e s u m a b l y arises f r o m the l o w site s y m m e t r y of the

9

groups w h i c h f u n c t i o n h e r e as b i d e n t a t e l i g a n d s .

Table VIII.

Vibrational Spectra of O x y and N i t r i d o Complexes X =

X = 0, cmr TERMINAL M-X 900-1060 300-400

VMX $mx

BRIDGING

N, cmr 1

1

950-1180 ca. 350

MmXn

Linear M - X - M V ¥

2

J

A

760-880 200-270

I

Linear VM x VM x 3

3

2

2

M - X - M - X - M

e

Triangular M v x* Mz

a

ca. 820 ca. 220

a e

3

1000-1160 260-370 ca. 1000

X 500-650 180-240

700-800 ca. 230

Comparison of the Vibrational Spectra of Oxy and Nitrido Complexes T a b l e V I I I shows the c h a r a c t e r i s t i c ranges of frequencies f o r s t r e t c h i n g a n d deformation modes for terminal a n d b r i d g i n g oxy a n d nitrido systems. I n e a c h case, t h e frequencies for the s t r e t c h i n g m o d e s are h i g h e r f o r n i t r i d e s t h a n f o r oxides. A l t h o u g h the n i t r o g e n a t o m is l i g h t e r t h a n o x y g e n , i t is l i k e l y t h a t this effect is c a u s e d i n l a r g e p a r t b y t h e f a c t t h a t


5. CLÉ ARE ET AL.

Nitrido Complexes

65


the nitride ligand is a more efficient ττ-donor than oxide—it is less electro negative and has more negative charge to impart to the metal atom (5).

Literature Cited (1) Bright, D., Ibers, J. Α., Inorg. Chem. 1969, 8, 709. (2) Chatt, J., Heaton, B. T., Chem. Commun. 1968, 274. (3) Ciechanowicz, M., Skapski, A.C.,Chem. Commun. 1969, 574. (4) Cleare, M. J., Griffith, W. P., Chem. Commun. 1968, 1302. (5) Cleare, M. J., Griffith, W. P.,J.Chem. Soc. 1970, A, 1117. (6) Clifford, A. F., Kobayashi, C. S., Inorg. Syn. 1960, 6, 204. (7) Cotton, F. Α., Lippard, S. J., Inorg. Chem. 1965, 4, 1621. (8) Delepine, M., Ann. Chim. (Paris) 1959, 1115, 1131. (9) Figgis, Β. N., Robertson, Ε. B., Nature 1965, 205, 695. (10) Griffith, W. P.,J.Chem. Soc. 1969, A, 2270. (11) Griffith, W. P.,J.Chem. Soc. 1965, 3694. (12) Jaeger, F. M., Zanstra, J. E., Proc. Acad. Sci. Amsterdam1932,35, 610 (13) Jorgensen, C. K., Acta Chem. Scand. 1959, 13, 196. (14) Jorgensen, C. K., Orgel, L. E., Mol. Phys. 1961, 4, 215. (15) Lecoq de Boisbaudran, Compt. Rend. 1883, 96, 1336, 1406, 1551. (16) Lewis, J., Wilkinson, G., J. Inorg. Nucl. Chem. 1958, 6, 12. (17) McCordie, W.C.,Watt, G. W., J. Inorg. Nucl. Chem. 1965, 27, 1130, 2013. (18) Morrow, J.C.,Acta Cryst. 1962, 15, 851. (19) Orgel, L. E., Nature 1960, 187, 505. (20) Potrafke, E. M., Watt, G. W., J. Inorg. Nucl. Chem. 1961, 17, 248. RECEIVED December 16, 1969.


6

Hydrido Group

Complexes of Platinum Metals


L. M. VENANZI State University of New York at Albany, Albany, Ν. Y. 12203

The preparation and properties of hydrido complexes of platinum group metals are reviewed briefly. The reactions of the more common hydrido complexes of iridium are sche matically shown. The reactions of complexes [IrHX (PhP)] (X = Cl, Br, and I), I, with the quadridentate ligand (o-Ph P · C H ) P, QP, are described and rationalized on the basis of the following reaction sequence: 2

3

3

2

6

4

3

I—HX [IrX(Ph P) ] heat [IrHX(0-C H PPh )(Ph P) ] 3

3

6

4

2

3

2

QP [IrH(0-C H PPh )(QP)]X +HX [IrHX(Ph P)(QP)]X Complexes of the latter two types have been assigned seven -coordinate structures on the basis of their proton and phos phorus-31 NMR spectra even though the oxidation number of the iridium atom is 3+. 6

4

2

3

A11 platinum group metals give hydrido complexes of general formula M H XpL (X = anionic ligand and L = uncharged ligand). Al though this field of chemistry is relatively new, its main development occurring over the last 10 years, the number of papers describing new compounds, their properties, and their reactions is very large and is growing at an increasing rate. Hydrido complexes also have been the subject of several reviews (9,11, 23, 24, 25,39), and the present one, like its predecessors, will be sadly out of date by the time it appears in print. As its title implies, this review restricts itself to describing and discuss ing compounds of platinum group metals—i.e., of ruthenium, rhodium, palladium, osmium, iridium, and platinum—although the compounds of the other transition elements and even some post-transition elements are either fully analogous or closely related to those of the platinum metals. n

m

q


6.

Hydrido

V E N A N Z I

Table I.

67

Complexes

Some Better Known Types of H y d r i d o Complex of the Platinum Metals' 1

Square

Planar

[PtH L ] [Ir-HX(LL)]

trans-[MBXL ] [IrH.(LL)] [M'(LL),]X

2

2

Five-Coordinate

[IrH L ] [IrH(CO) L ]

[IrH L ]X [M'H(CO)L,] 2

3

3

Octahedral 2

!

n

2

n

2

2

2

2

2

2

[IrH L 'L ]X [IrH L'L ]X [M'H X _ L ]

2

2

2

2

[PtH X L ] [M HX (CO)L ] [M"H X . (LL) [M"HX(CO)L ] 2

2

3

m

2

3

m

3


3

° M M L m

1

"

M ' = R h or Ir L = monodentate phosphine L L = bidentate phosphine η = 1 or 2

= P d or Pt = R u or Os = C O or monodentate phosphine = 1, 2, or 3

E v e n w i t h i n this l i m i t a t i o n , the subject is vast a n d , therefore, no a t t e m p t is m a d e to give a c o m p r e h e n s i v e d e s c r i p t i o n of the

field.

A s u r v e y of the c o m p o u n d s r e p o r t e d i n the l i t e r a t u r e shows t h a t the f o r m a t i o n of stable h y d r i d o complexes g e n e r a l l y is l i n k e d w i t h the p r e s ence i n the m o l e c u l e of one or m o r e of c e r t a i n types of l i g a n d s , the m o s t frequently occurring being carbon monoxide, phosphorus ( I I I ) senic ( I I I ) d e r i v a t i v e s , a n d the c y c l o p e n t a d i e n e

and ar

group.

I t is u s e f u l to classify the complexes b y t h e i r c o o r d i n a t i o n n u m b e r . T h e m a j o r i t y of t h e m are six-coordinate w i t h o c t a h e d r a l s t r u c t u r e , a l though four- and seven-coordinate

five-coordinate

species are n u m e r o u s , a n d e v e n some

species are k n o w n .

T a b l e I shows a list of the m a i n

types of c o m p o u n d s r e p o r t e d i n the l i t e r a t u r e . P r e p a r a t i v e m e t h o d s for h y d r i d o complexes

vary widely.

Some

the m o r e f r e q u e n t l y u s e d of t h e m a r e : (1)

A c t i o n of c o m p l e x h y d r i d e s ,

e.g., LiAlH

4

as-[RuCl (Me PCH CH PMe ) ] 2

2

2

2

2

>

2

imns-[RuHCl(Me PCH CH PMe ),] 2

(2)

2

2

2

A c t i o n of alcohols i n the presence of a base,

(16)

e.g.,

Ph P 3

(NH ) [OsBr ]< 4

2

6

• [ O s H B r ( C O ) ( P h P ) ] (41) MeOCH CH OH 3

2

(3)

P r o t o n a t i o n of complexes,

3

2

e.g., H+

[Ru (x-C H ) (CO) ] 2

5

5

2

6

> [Ru H(x-C H ) (CO) ]+ 2

5

5

2

6

(20)


of

68 (4)

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

A c t i o n of h y d r a z i n e , e.g., N H 2

· H 0 > i r a r c s - [ P t H C l ( E t P ) ] (17)

4

2

cie-[PrCl,(Et«P)J

3

2

H y d r i d o complexes are also f o r m e d i n some u n u s u a l r e a c t i o n s : MeOCH CH OH > [ P h A s ] [ P d H C l ( C O ) ] (27) at r o o m t e m p . 2

(1) P d C l + C O + [ P h A s ] C l 2

4

2

4

H 0 > [PtHI (Pr P) ]

2

2

(2) [ P t I ( M g I ) ( P r P ) ] 3

2

3

(19)

2

Some of the p r e p a r a t i v e m e t h o d s are best d e s c r i b e d , at least f o r m a l l y , as i n v o l v i n g a n " o x i d a t i v e a d d i t i o n " of a m o l e c u l e to a c o m p l e x of a m e t a l Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

i o n or a t o m i n a l o w o x i d a t i o n state. E x a m p l e s of this t y p e of r e a c t i o n are shown below. (1)

A d d i t i o n of m o l e c u l a r h y d r o g e n , H

[Rh(Me PCH CH PMe ) ]Cl 2

(2)

2

2

2

e.g.,

2

•aV[RhH (Me PCH CH PMe ) ]Cl

2

2

A d d i t i o n of h y d r o g e n h a l i d e ,

2

2

2

2

2

(12)

e.g.,

HC1 [Rh(Ph PCH CH PPh ) ]Cl 2

(3)

2

2

2

• a s - [ R h H C l ( P h P C H C H P P h ) ] C l (38)

2

2

A d d i t i o n of other h y d r i d e s ,

2

2

2

2

e.g.,

H S [Pt(Ph P) ] — U 3

* m n s - [ P t H ( S H ) ( P h P ) ] (35)

3

3

2

A p a r t i c u l a r l y i n t e r e s t i n g t y p e of o x i d a t i v e a d d i t i o n r e a c t i o n is the " h y d r o g e n a b s t r a c t i o n " r e a c t i o n , some examples of w h i c h are g i v e n b e l o w . (1) [ R u ( M e P C H C H P M e ) ] [ R u H ( C H P ( M e ) C H C H P M e ) 2

2

2

2

2

2

(Me PCH CH PMe )] 2

2

2

2

2

2

2

(U)

heat (2) [ I r C l ( P h P ) ] 3

• [ I r H C l ( o - C H P P h ) ( P h P ) ] (7)

3

6

(3) i m n s - [ P t C l ( E t P ) ] + L i C B 2

3

2

1 0

H

1 0

4

2

3

2

C M e -> [ P t ( C B H C M e ) 1 0

1 0

( C H C H P E t ) ( E t P ) ] (8) 2

2

2

3

T h e s e reactions are of p a r t i c u l a r interest as t h e y c o u l d p r o v i d e the basis f o r a n u m b e r of c a t a l y t i c processes i n v o l v i n g s a t u r a t e d h y d r o carbons. T h e p r o p e r t i e s of h y d r i d o complexes v a r y w i d e l y , r a n g i n g f r o m those w h i c h c a n b e d e t e c t e d o n l y s p e c t r o s c o p i c a l l y to those that s h o w r e m a r k a b l e g e n e r a l c h e m i c a l s t a b i l i t y . S t a b i l i t y g e n e r a l l y tends to b e at a m a x i m u m i n c o m p o u n d s of the t h i r d t r a n s i t i o n series. F u r t h e r m o r e , f o r a g i v e n m e t a l a n d t y p e of c o m p l e x , s t a b i l i t y appears to b e at its h i g h e s t w h e n


6.

Hydrido

V E N A N Z I

69

Complexes

p h o s p h i n e l i g a n d s are present i n the m o l e c u l e .

Naturally, it w o u l d

be

f o o l h a r d y to take the a b o v e k i n d of s t a b i l i t y as a g u i d e to t h e r m o d y n a m i c s t a b i l i t y of the m e t a l - h y d r o g e n b o n d , as one w o u l d d r a w a c o r r e l a t i o n b e t w e e n a s t a b i l i t y w h i c h is a c o m p o s i t e of a n u m b e r of t h e r m o d y n a m i c a n d k i n e t i c factors a n d a r e l a t i v e l y s m a l l energy t e r m s u c h as the M - H b o n d energy. I t is regrettable that t h e r m o d y n a m i c d a t a o n h y d r i d o c o m plexes are t o t a l l y l a c k i n g b u t t h e y are almost i m p o s s i b l e to o b t a i n . T h e most c o m m o n l y

quoted physical data on hydrido

are the v i b r a t i o n a l spectra a n d p r o t o n m a g n e t i c resonance

complexes parameters.

H y d r i d o complexes e x h i b i t M - H s t r e t c h i n g v i b r a t i o n s i n the r e g i o n 1 7 0 0 2250 c m

- 1

a n d M - H b e n d i n g m o d e s i n the r e g i o n 6 6 0 - 8 5 0

cm . - 1

The

absence of a b s o r p t i o n i n the a b o v e regions, h o w e v e r , is not to b e t a k e n Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

as a n i n d i c a t i o n t h a t the m o l e c u l e u n d e r e x a m i n a t i o n does not c o n t a i n M - H bonds.

S e v e r a l h y d r i d o complexes are k n o w n w h e r e M - H b o n d s

w e r e not detectable b y i n f r a r e d spectroscopy

(28, 34, 37).

Proton mag

n e t i c resonance, o n the other h a n d , is a m o r e g e n e r a l l y u s e f u l t e c h n i q u e . P r o t o n resonances i n h y d r i d o complexes h a v e v e r y c h a r a c t e r i s t i c τ-values r a n g i n g f r o m 11 to 42 p p m r e l a t i v e to T M S . T h e l i m i t a t i o n here is i n t r o d u c e d b y s o l u b i l i t y a n d b y fast exchange p h e n o m e n a a l t h o u g h , i n m a n y cases, the f o r m e r difficulty c a n be o v e r c o m e b y s p e c t r u m a c c u m u l a t i o n a n d the latter b y l o w e r i n g the s a m p l e t e m p e r a t u r e . H y d r i d o l i g a n d s e x h i b i t a v e r y strong trans effect w h i c h appears to operate m a i n l y b y a l a b i l i z a t i o n of the b o n d i n trans p o s i t i o n to the M - H b o n d . T h i s l a b i l i z a t i o n g e n e r a l l y is associated w i t h a l e n g t h e n i n g of the b o n d w h i c h has b e e n l a b i l i z e d , a n effect o p e r a t i n g m a i n l y b y trans i n fluence

(36)

c a u s e d b y a selective r e h y b r i d i z a t i o n of the m e t a l σ orbitals

l e a d i n g to the M - H b o n d h a v i n g a large d a n d s c o m p o n e n t .

S u c h effects

are most e v i d e n t i n square p l a n a r complexes, b u t t h e y also h a v e observed i n octahedral

been

complexes.

T h e g e n e r a l r e a c t i v i t y of h y d r i d o complexes is h i g h , a n d i t is r e l a t e d m a i n l y to the c o o r d i n a t i o n n u m b e r of the c e n t r a l m e t a l a t o m . four- a n d

five-coordinate

six-coordinate species.

Thus,

complexes u s u a l l y are m o r e r e a c t i v e t h a n r e l a t e d T h e latter, h o w e v e r , o r d i n a r i l y are m o r e r e a c t i v e

t h a n the c o r r e s p o n d i n g complexes

w h i c h d o not c o n t a i n M - H b o n d s .

S u c h r e a c t i v i t y m a y b e i n d u c e d either b y o p e r a t i o n of the trans effect or, w h e r e possible, b y the r e d u c t i v e e l i m i n a t i o n of a m o l e c u l e of h y d r o g e n h a l i d e w i t h or w i t h o u t assistance of a base. T h e c h e m i c a l b e h a v i o r of M - H b o n d s varies f r o m t h a t of a n a c t i v e h y d r i d e to that of a strong a c i d . T h i s w i d e v a r i a t i o n i n p r o p e r t i e s , h o w ever, m a y be a c h i e v e d w i t h a r e l a t i v e l y s m a l l v a r i a t i o n of c h a r g e d i s t r i b u t i o n (4).

A t t e m p t s to correlate c h e m i c a l shifts a n d c o u p l i n g constants

w i t h b o n d distances a n d electron d i s t r i b u t i o n i n M - H b o n d s h a v e l e d


70

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

t o t h e c o n c l u s i o n that s u c h correlations m a y b e v a l i d o n l y w h e n v e r y s m a l l changes are m a d e to the l i g a n d s

(3).

T h e f e v e r i s h interest i n h y d r i d o complexes

has, as its m a i n cause,

the t r e m e n d o u s p o t e n t i a l of these reactions i n c a t a l y t i c systems.

In a

r e l a t i v e l y short s p a n of t i m e , h y d r i d o complexes h a v e b e e n f o u n d to p l a y a r o l e i n a significant n u m b e r of c a t a l y t i c processes ( 6 , 9)—e.g., o l i g o m e r i z a t i o n of olefins ( r h o d i u m ) , d e c a r b o x y l a t i o n reactions

(rhodium),

a n d hydrogénation reactions ( r u t h e n i u m , o s m i u m , r h o d i u m , i r i d i u m , a n d p l a t i n u m ) . D i s c u s s i o n of these a p p l i c a t i o n s w o u l d go b e y o n d the scope of the present treatment. T h e r e m a i n d e r of this r e v i e w is d e v o t e d to g i v i n g a closer l o o k at the h y d r i d o complexes of i r i d i u m a n d t h e i r reactions. I r i d i u m gives the Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

most extensive a n d versatile range of h y d r i d o complexes of a n y p l a t i n u m metal (29).

T h e m a i n types of c o m p o u n d s

k n o w n a n d some of t h e i r

reactions are s h o w n i n T a b l e I I . T o this, one m u s t a d d the

hydrogen

a b s t r a c t i o n r e a c t i o n m e n t i o n e d earlier. T h e w i d e r a n g e of h y d r i d o complexes f o r m e d b y i r i d i u m is a c l e a r i n d i c a t i o n t h a t this m e t a l has a p a r t i c u l a r l y strong t e n d e n c y to f o r m I r - H bonds.

T h e reason for this affinity is n o t a p p a r e n t as yet, b u t this c o n -

c l u s i o n is r e i n f o r c e d constantly b y n e w d a t a . T h u s , one c a n isolate stable seven-coordinate

complexes

of i r i d i u m ( I I I ) .

T h e quadridentate ligand

( o - P h P · C H ) P , Q P , reacts w i t h [ I r H X ( P h P ) ] ( X = 2

6

4

3

2

3

CI, Br, and

8

I ) i n r e f l u x i n g c h l o r o b e n z e n e to give [ I r H X ( P h P ) ( Q P ) ] X , I , w h i c h is 3

a seven-coordinate h y d r i d o c o m p l e x of i r i d i u m ( I I I ) .

(21)

The infrared

s p e c t r u m does n o t s h o w a n I r - H s t r e t c h i n g v i b r a t i o n , b u t t h e presence of a h y d r i d o l i g a n d is c l e a r l y v i s i b l e i n the p r o t o n m a g n e t i c

resonance

spectrum. T h e f o r m a t i o n of these c o m p o u n d s is p r e c e d e d b y that of a species of c o m p o s i t i o n

[ I r ( P h P ) ( Q P ) ] X , I I , w h i c h reacts w i t h N a [ B P h ] 3

to

4

g i v e the same c o m p l e x i r r e s p e c t i v e of the n a t u r e of the a n i o n X i n the s t a r t i n g m a t e r i a l , [ I r H X ( P h P ) ] . T h e i r N M R s p e c t r a (22) 2

3

[IrHX(Ph P)(QP)]X. 3

indicate

3

the presence of I r - H b o n d s a n d t h e i r r e a c t i o n w i t h H X gives

compounds

C o m p l e x e s I I are, therefore, t e n t a t i v e l y f o r m u -

l a t e d as [ I r H ( o - C H P P h ) ( Q P ) ] X . 6

4

2

I n a n a t t e m p t to g a i n a better u n d e r s t a n d i n g of the factors c a u s i n g t h e f o r m a t i o n of the a b o v e seven-coordinate h y d r i d o complexes, the r e a c t i o n of [ I r H C l ( P h P ) ] w i t h r e f l u x i n g c h l o r o b e n z e n e 2

3

3

was e x a m i n e d .

P r e l i m i n a r y experiments suggest that the p r i m a r y step is t h e e v o l u t i o n of

hydrogen

chloride

and

formation

of

the

unstable

intermediate

[ I r C l ( P h P ) ] , w h i c h reacts f u r t h e r to g i v e a n u m b e r of p r o d u c t s . 3

3

has the c o m p o s i t i o n I r C l ( P h P )

3

III,

compound

3

of

Bennett

and

Milners

One

a n d is l i k e l y to b e a n i s o m e r i c f o r m , (7),

[IrHCl(o-C H PPh )6

4

2

( P h P ) ] . T h e others, s o m e p u r e l y o r g a n i c a n d some i r i d i u m - c o n t a i n i n g , 3

2


6.

Hydrido

V E N A N Z I

Table II.

Y

Some Iridium H y d r i d o Complexes and T h e i r Reactions

2

3

(44)

HX

->

[IrH L ](C10

20,000

M ' . F o r a p u r e s o l u t i o n , a 10-cm c e l l w i l l y i e l d a n absorbance

1

1

of

0.1 f o r a 0.5 μΜ s o l u t i o n . H i g h sensitivity i n analysis is therefore p o s sible, p r o v i d e d

interferences

P t C U " at 30,000 c m 2

P t B r ~ is 10,000 c m " 6

2

are absent.

is 600 c m

1

1

- 1

The

m o l a r a b s o r p t i v i t y for

M " , whereas t h e m o l a r a b s o r p t i v i t y for 1

M " . It is possible f r o m the spectra, therefore, to 1


7.

Ultraviolet

M A R T I N

Spectroscopic

77

Qualities

p l a c e a f a i r l y s m a l l l i m i t u p o n the c o n t a m i n a t i o n b y the P t B r ' w h i c h 2

6

m a y b e present. W h e r e a s the h e i g h t of a s p e c t r a l p e a k is a g o o d measure for the c o n c e n t r a t i o n of the p r e d o m i n a n t species, the a b s o r b a n c e

at a

s p e c t r a l v a l l e y is v e r y sensitive to the presence of i m p u r i t i e s . F o r s y n thetic p r e p a r a t i o n s , one of the most r e l i a b l e c r i t e r i a of p u r i t y is the peak-to-valley ratio i n an absorption spectrum. A very valuable prepara tive technique involves continued fractional recrystallization u n t i l such a p e a k - t o - v a l l e y r a t i o does n o t increase u p o n e a c h s u b s e q u e n t tallization.


°h

D

4

h

. .η* M c h a r g e transfer. S u c h transitions are expected to l e a d to b a n d s w i t h the m o l a r a b s o r p t i v i t y ,C.,at the p e a k greater t h a n 1000 c m " M " . T r a n s i t i o n s 1

of electrons f r o m t

2g

1

to t * w o u l d b e a l l o w e d b y s y m m e t r y , a n d the lu

p o s s i b i l i t y of t h e i r presence i n the spectra m u s t b e c o n s i d e r e d as w e l l . H o w e v e r , i n most instances t h e y are b e l i e v e d to o c c u r at h i g h e r energy, f r e q u e n t l y b e y o n d the r a n g e of observations w i t h h a l i d e s . T r a n s i t i o n s of a n e l e c t r o n f r o m a t

2g

bidden.

o r b i t a l to e * are d i p o l e - f o r g

B a n d s w i t h a m o l a r a b s o r p t i v i t y of the order of 100 c m " M " 1

1

u s u a l l y are assigned to s u c h d-d transitions i n w h i c h the spins are u n changed—i.e.,

t h e y are s p i n - a l l o w e d .

Since the h e a v y metals h a v e a

h i g h s p i n - o r b i t c o u p l i n g , a n d the s p i n is n o l o n g e r a g o o d q u a n t u m n u m b e r b y the m i x i n g of different m u l t i p l e t states, b a n d s are

observable

b e t w e e n states w h i c h h a v e m a j o r components w i t h different s p i n m u l t i plicities.

T h e s e are d e s i g n a t e d as the s p i n - f o r b i d d e n b a n d s .

the m i x i n g of states is sufficiently great that there m a y b e

Indeed,

considerable

a m b i g u i t y i n the assignment of transitions. T h e s i t u a t i o n is t r e a t e d b y c o n s i d e r i n g the d o u b l e

r o t a t i o n a l groups

o r b i t a l a n d s p i n w a v e functions.

w h i c h encompass

both

the

F o r e x a m p l e , the electron s p i n f u n c -


7.

M A R T I N

Ultraviolet

Spectroscopic

79

Qualities

tions, + 1 / 2 , — 1 / 2 , are b a s i c f u n c t i o n s f o r t h e y*(e ) 2

irreducible repre

sentation f o r the O ' g r o u p . S i n g l e t a n d t r i p l e t f u n c t i o n s h a v e γ ι ( α ι ) a n d 7 (*i)

symmetry, respectively.

4

T h e a c t u a l states m a y b e f o r m e d

from

a l i n e a r c o m b i n a t i o n o f w a v e functions w i t h different m u l t i p l i c i t i e s . T h e c o n t r i b u t i o n o f m i n o r m u l t i p l i c i t i e s m a y b e sufficiently great t h a t " s p i n a l l o w e d " transitions h a v e a n e n h a n c e m e n t f a c t o r o f o n l y 4 t o 10 over " s p i n - f o r b i d d e n " transitions.

A s the wavelength

decreases,

q u e n t l y possible to observe i n a s p e c t r u m first s o m e symmetry-forbidden

i t is f r e

spin-forbidden,

transitions, t h e n t h e s p i n - a l l o w e d b u t s y m m e t r y -

f o r b i d d e n , a n d finally some c h a r g e transfer b a n d s .

However, only a

f r a c t i o n o f the possible transitions are observable, a n d m a n y are " h i d d e n " u n d e r t h e b r o a d peaks o f m o r e intense transitions i n s o l u t i o n spectra o f Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

the t y p e i l l u s t r a t e d i n F i g u r e 1. T h e o r y has n o t y e t r e a c h e d a stage w h e r e energies o r e v e n t h e o r d e r i n g o f states c a n b e c a l c u l a t e d r e l i a b l y f o r t r a n s i t i o n e l e m e n t plexes.

Therefore,

complementary

com

contributions a n d cooperation b e

tween experiment a n d theory are needed i n the unravelling of energy states a n d t h e d e s c r i p t i o n o f b o n d i n g f o r these i m p o r t a n t systems. T h e ^ - c o n f i g u r a t i o n , w h i c h occurs for t h e m u l t i t u d e o f i n e r t C o ( I I I ) complexes, is i l l u s t r a t e d b y the complexes o f I r ( I I I ) a n d the P t ( I V ) c o m plexes i n F i g u r e 1. T h e g r o u n d state c o n f i g u r a t i o n is p r i m a r i l y t

G

S i n c e the t

2g

—

o r b i t a l s a r e filled, there is n o p o s s i b i l i t y o f a t r a n s i t i o n

2g

f r o m t h e l i g a n d π-orbital i n t o o n e o f these; therefore, charge transfer b a n d s w i l l i n v o l v e o n l y t r a n s i t i o n to t h e a n t i b o n d i n g e *. g

b a n d p e a k i n g at 38,000 c m "

1

w i t h c o f 24,000 c m "

a t t r i b u t e d to s u c h t r a n s i t i o n b y Jorgensen.

T h e strong

M " for P t C l " was

1

1

6

T h e t r a n s i t i o n ir(t )

2

-> ^*

lu

leads to f o u r energy levels w h o s e p r i n c i p a l c o m p o n e n t s are T \ , *T*2 , T±u? 1

T .

3

2u

M

U

3

B e c a u s e o f the £i c h a r a c t e r o f the t r i p l e t s p i n f u n c t i o n s , transitions

to the p r i m a r i l y T , l

lu

T,

3

lu

states a l l h a v e some d i p o l e - a l l o w e d c h a r

T

3

2u

acter. H o w e v e r , n o r e s o l u t i o n i n t o s u c h i n d i v i d u a l states is possible w i t h the o b s e r v e d b a n d n o r c a n a n y d e c i s i o n b e presented as to w h e t h e r a contribution from ττ(ί ) -> e 2ΐί

g

occurs as w e l l .

T h e r e is t h e p o s s i b i l i t y

of a s y m m e t r y - f o r b i d d e n t r a n s i t i o n o f o n e o f t h e t

2g

e *. g

electrons i n t o t h e

T h e e x c i t e d e l e c t r o n i n e i t h e r o f t w o o r b i t a l s a n d the r e s i d u a l h o l e i n

a n y o f three leads to a t o t a l o f six singlet a n d six t r i p l e t states.

However,

these six states i n e a c h case constitute t w o t h r e e - f o l d degenerate sets; t h e l o w e r i n e n e r g y c a n b e d e s i g n a t e d as T

lg

a l l o w e d b a n d s s h o u l d o c c u r , therefore.

and a higher T .

T w o spin-

A s indicated w i t h

Jorgensens

2g

assignment i n F i g u r e 1, o n l y the first t r a n s i t i o n c a n b e seen as a s h o u l d e r o n the m u c h m o r e intense c h a r g e transfer b a n d . T h e s t i l l l o w e r intensities i n t h e r e g i o n o f 19,000 to 24,000 c m "

1

w i l l correspond then to t h e spin-

forbidden symmetry-forbidden bands.


80

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

F o r the h e x a b r o m o p l a t i n a t e ( I V ) , there has b e e n a d e c i d e d shift of a l l b a n d s to l o w e r energies or l o n g e r w a v e l e n g t h s , a n d the b r e a d t h of the c h a r g e transfer b a n d definitely suggests m o r e t h a n a single e x c i t e d state. T h i s e n e r g y shift b e t w e e n c h l o r i d e a n d b r o m i d e l i g a n d s is q u i t e a g e n e r a l phenomenon

r e p r e s e n t i n g the p o s i t i o n of these l i g a n d s i n the

c h e m i c a l (sometimes

c a l l e d the F a j a n s - T s u c h i d a ) series.

spectro-

T h e shift of

t h e c h a r g e transfer b a n d reflects the easier o x i d a t i o n or loss of a n elec t r o n b y b r o m i d e i n c o m p a r i s o n w i t h c h l o r i d e . H o w e v e r , the shift i n the d-d t r a n s i t i o n represents the difference i n the c r y s t a l field s t r e n g t h of these t w o l i g a n d s . T h e I r C l " i o n , w i t h the same e l e c t r o n c o n f i g u r a t i o n as t h e 6

3

t w o p l a t i n u m complexes, h o w e v e r , is i n a l o w e r o x i d a t i o n state. A d d i t i o n a l e n e r g y is r e q u i r e d to a d d a n electron to the i r i d i u m , a n d

consequently


the charge transfer b a n d has b e e n f o r c e d to m u c h h i g h e r energies. the transitions to the t w o e x c i t e d states, p r i m a r i l y discernable. T h e occurrence

and T , 1

2g

Here,

are c l e a r l y

of the d-d b a n d s at l o w e r energies

corre

sponds to a l o w e r Δ for I r ( I I I ) t h a n for P t ( I V ) , w h i c h is i n a c c o r d a n c e 0

w i t h the u s u a l systematics i n this q u a n t i t y (19). h i g h - i n t e n s i t y b a n d , 31,000-32,000

T h e b r e a d t h of

c m " , p r o b a b l y reflects 1

the

the

higher

s p i n - o r b i t c o u p l i n g of the b r o m i d e l i g a n d s i n c o m p a r i s o n w i t h that of chloride. F o r I r ( I V ) i n I r C l " , there is a h o l e i n the t 6

g r o u n d state, t

5

2g

2

— T . 2

2g

2g

one of t h e l i g a n d ττ-orbitals i n t o a t

2g

proposed

o r b i t a l set for the

T h e r e f o r e , the t r a n s i t i o n of a n e l e c t r o n f r o m o r b i t a l is possible. J o r g e n s e n

(17)

that these c h a r g e transfer b a n d s w e r e the ones seen i n the

v i s i b l e r e g i o n , 20,000-25,000 c m " , w h i c h h a d c's of 2 0 0 0 - 4 0 0 0 c m " M " . 1

1

1

T h e s e b a n d s p r o v i d e the intense color f o r I r C l " so t h a t its presence i n 6

2

m i n u t e amounts c a n b e d e t e c t e d e a s i l y i n solutions of I r C l " . e

T h e pres

3

ence of h y p e r f i n e s t r u c t u r e o n the electron s p i n resonance s p e c t r u m of this ( 8 , 25)

i o n i n d i c a t e d t h a t the t

2g

orbitals were not solely metal

orbitals, b u t that t h e y c o n t a i n e d significant l i g a n d o r b i t a l character. T h i s feature

demonstrated

the

existence

of

some ττ-type

bonding

in

the

complex. F o r O s ( I V ) , there are t w o electrons m i s s i n g f r o m a filled set of orbitals. T h e r e f o r e , t r a n s i t i o n f r o m the l i g a n d ττ-orbitals to the t

2g

s h o u l d a g a i n b e possible.

Since O s ( I V )

t

2g

orbitals

is a m u c h w e a k e r o x i d i z i n g

agent t h a n I r ( I I I ) , i t is e x p e c t e d t h a t these c h a r g e transfer b a n d s w i l l b e s h i f t e d to h i g h e r energies.

T h e spectrum i n F i g u r e 1 indicates that

an a b s o r p t i o n p a t t e r n v e r y s i m i l a r to that f o r I r C l " occurs f o r O s C l " . 6

2

A c c o r d i n g l y , Jorgensen assigned the b a n d s f r o m 28,500-30,000 these L ->

t

2g

to b e o b s e r v e d .

6

cm"

1

2

to

transitions. T h e O s C l " s p e c t r u m is one of the r i c h e s t 6

2

S t i l l , o n l y a h a n d f u l of i n c o m p l e t e l y r e s o l v e d

b a n d s i n the s o l u t i o n s p e c t r u m are seen.

broad

Since a considerably larger


7.

Ultraviolet

M A R T I N

Spectroscopic

81

Qualities

n u m b e r of s u c h c h a r g e transfer states m a y b e a t t a i n e d b y d i p o l e - a l l o w e d transitions t h a n are o b s e r v e d , a d e t a i l e d c o n f i r m a t i o n of this a s s i g n m e n t has not b e e n possible. Some v e r y r e c e n t i n f o r m a t i o n , w h i c h w i l l b e d i s cussed later, has b r o u g h t this assignment of these b a n d s i n t o q u e s t i o n . F i g u r e 1 does s h o w t w o v e r y w e a k , r e l a t i v e l y s h a r p b a n d s t h a t o c c u r at a p p r o x i m a t e l y 17,000 c m "

1

for O s C l " w h i c h a r e not o b s e r v e d i n the

other s p e c t r a p r e s e n t e d .

T h e s e are b e l i e v e d to represent a t r a n s i t i o n

6

2

w i t h i n the g r o u n d state c o n f i g u r a t i o n — L e . , t* gTi( T ) 2

w e a k e r transitions (12)

3

-> Γ Ί ^ Α ^ ) .

lg

Still

h a v e b e e n o b s e r v e d at a b o u t 8000, 10,800, a n d

11,780 c m " . 1

M a n y features of t h e s p e c t r a of the o c t a h e d r a l complexes s e e m e d consistent w i t h s i m p l e m o l e c u l a r o r b i t a l m o d e l s .

have

The high sym


m e t r y possessed b y these complexes f o r t u n a t e l y has r e d u c e d the n u m b e r of i n d i v i d u a l transitions w h i c h s h o u l d o c c u r because of the m a n y d e generate states for the i o n . T h e broadness of the f e w b a n d s

observed,

h o w e v e r , p r e c l u d e s r e s o l u t i o n of the f a i r l y l a r g e n u m b e r of transitions w h i c h m i g h t b e e x p e c t e d to h a v e m e a s u r a b l e intensities as a c o n s e q u e n c e of s p i n - o r b i t c o u p l i n g .

T h e b r e a d t h of the a b s o r p t i o n b a n d s at least

p a r t i a l l y arises f r o m t h e r m a l l y e x c i t e d of the c o o r d i n a t i o n c o m p l e x .

fluctuations

i n the e n v i r o n m e n t

F o r e x a m p l e , i n the g r o u n d state a b o n d

m a y be lengthened b y a molecular vibration. T h e vibrational energy i n this m o d e w i l l a m o u n t to o n l y a b o u t kT.

H o w e v e r , because

of the

F r a n k - C o n d o n p r i n c i p l e , the e x c i t e d i o n w i l l h a v e the same i n t e r - a t o m i c distances as the g r o u n d state. T h u s , i f the e x c i t e d state i o n has a steep p o t e n t i a l e n e r g y f u n c t i o n for a t o m i c separations at the t r a n s i t i o n c o n figuration,

a v i b r a t i o n a l d i s p l a c e m e n t of m o d e s t e n e r g y i n the g r o u n d

state w i l l p r o d u c e l a r g e energy differences i n the e x c i t e d c o m p l e x .

A

r e d u c t i o n i n t e m p e r a t u r e w i l l l e a d a c c o r d i n g l y to m u c h n a r r o w e r a n d better resolved bands.

Spectrum of

PtCl/'

T h e P t C l " i o n , w i t h the 2 + 4

a 5d

8

2

o x i d a t i o n state for p l a t i n u m , possesses

c o n f i g u r a t i o n . I t has a s q u a r e - p l a n a r c o o r d i n a t i o n , w h i c h is c o m

m o n l y o b s e r v e d w i t h the l o w s p i n complexes of this c o n f i g u r a t i o n .

Its

a b s o r p t i o n s p e c t r u m i n aqueous s o l u t i o n is also s h o w n i n F i g u r e 1.

With

the p l a t i n u m i n a l o w o x i d a t i o n state, the c h a r g e transfer b a n d s

have

b e e n s h i f t e d to b e y o n d 40,000 c m " . 1

S i n c e P t C l ~ absorbs so s t r o n g l y at 38,000 c m " , the a b s o r b a n c e 6

2

1

at

this w a v e n u m b e r c a n b e u s e d to set a v e r y l o w l i m i t of d e t e c t i o n o n the presence of P t ( I V ) i n samples of P t C l " . 4

2

T h i s is e s p e c i a l l y v a l u a b l e ,

since the h i g h e r o x i d a t i o n state has sometimes

been

suspected

catalyst f o r some of its reactions.


as a

82

PLATINUM

GROUP

T h e m o l e c u l a r o r b i t a l scheme f o r t h e D

4h

METALS

AND COMPOUNDS

s y m m e t r y , possessed b y

this i o n , i s s h o w n i n F i g u r e 2. A l t h o u g h t h e i o n is h i g h l y s y m m e t r i c , the s y m m e t r y is sufficiently l o w that i n f o r m a t i o n f r o m p o l a r i z e d spectra of crystals is v e r y u s e f u l i n e s t a b l i s h i n g assignments f o r t h e transitions. T h e peaks at 25,400 a n d 30,300 c m " , w i t h e a b o u t 60, are c l e a r l y s p i n 1

a l l o w e d d-d transitions. I t w a s n o t c l e a r w h e t h e r t h e s m a l l e r p e a k a t a b o u t 20,000 c m " corresponds 1

s i m i l a r l y to a s p i n - a l l o w e d t r a n s i t i o n o r

to one w h i c h is s p i n - f o r b i d d e n . F i g u r e 2 shows a p o s s i b i l i t y o f three s p i n a l l o w e d transitions f r o m t h e filled d-orbitals i n t o t h e a n t i - b o n d i n g o r the d . 2

x

o r b i t a l . I n s u c h a t r a n s i t i o n , t h e e l e c t r o n leaves a s y m m e t r i c

2

y

( g ) o r b i t a l a n d moves i n t o a s y m m e t r i c ( g ) o r b i t a l , so t h e t r a n s i t i o n is therefore d i p o l e - f o r b i d d e n .

H o w e v e r , these transitions b e c o m e a l l o w e d


i n t h e presence o f a n a s y m m e t r i c the c h e m i c a l e n v i r o n m e n t — i . e . ,

field.

S u c h a field m a y r e s u l t f r o m

t h e effect o f n e i g h b o r i n g m o l e c u l e s o r

ions i n a s o l u t i o n o r i n a c r y s t a l . I t c a n also r e s u l t f r o m t h e a s y m m e t r i c vibrations of the complex. vibronically exicited.

I n t h e latter case, t h e t r a n s i t i o n is s a i d to b e

I n quantum mechanical description, the vibration

is c o n s i d e r e d a p e r t u r b a t i o n o n t h e system.

T h u s , t h e electronic

wave

f u n c t i o n , ^ i ct, is represented b y t h e e q u a t i o n e

e

d . . 2

x

2

y

w i t h better r e s o l u t i o n a r e

expected, a n d the v i b r o n i c m o d e l p r e d i c t s l o w e r intensities as w e l l . T h e p o l a r i z e d spectra at l i q u i d h e l i u m temperatures c o n f i r m these p r e d i c t i o n s . T h u s , shoulders a t 24,000 c m "

1

a n d i n the r e g i o n o f 17,000-19,000


cm"

1

PLATINUM

84

GROUP

METALS

AND

w h i c h c o u l d not b e r e s o l v e d at r o o m t e m p e r a t u r e n o w clearly.

COMPOUNDS

are r e s o l v e d

A n i n t e r e s t i n g feature is the fine s t r u c t u r e w h i c h a p p e a r e d o n

t h e t w o b a n d s f r o m 23,000-28,000 c m " , w h e r e 17 i n d i v i d u a l p e a k s c a n b e 1

seen.

T h e s e i n d i v i d u a l peaks result f r o m e x c i t a t i o n of the t o t a l l y s y m

m e t r i c , b r e a t h i n g v i b r a t i o n i n the e x c i t e d

electronic

states.

Weaker

v i b r a t i o n a l structure c o u l d b e d i s c e r n e d , e s p e c i a l l y i n ζ p o l a r i z a t i o n for the b a n d c e n t e r e d o n 20,600 c m " . 1

H o w e v e r , n o s u c h structure w a s

e v i d e n t o n t h e strong b a n d a t 29,600 c m " . 1

A n i n t e r e s t i n g conjecture

is t h a t b a n d s for w h i c h t h e v i b r a t i o n a l

structure is m i s s i n g i n v o l v e transitions to e x c i t e d electronic states w h i c h


60

Έ υ 7

40 * 20 0

+

2.0

«•

Ο

<
P t C l ( H 0 ) - + C I " 4

2

2

3

(3)

2

the s p e c t r u m is i n t e r m e d i a t e b e t w e e n the t w o s h o w n i n F i g u r e 7.

The

s p e c t r u m for P t C l ( H 0 ) " w a s o b t a i n e d f r o m the o b s e r v e d e q u i l i b r i u m 3

2

s p e c t r u m a n d the e q u i l i b r i u m concentrations of the species.

T h e spec-



88

P L A T I N U M

10

Figure 7.

χ

M E T A L S

A N D

C O M P O U N D S

χ cm"

Absorption spectrum in dilute aqueous HCl of the com plexes, PtClf', PtCl (H 0); and PtCl (NH )s

6.00 X I0~

(5

3

M

Rb PtBr 2

8.

3

s

4

BQJJ

40

2

160

TIME IN

Figure

ν

GROUP

180

2ÔÔ

220

MINUTES

Changes in the absorbance solved in H 0

after RbzPtBr^

is dis-

2

Wavelength, 415

πΐμ.

NaNOs added to give an ionic strength of 0.318M. H\ 10- M. S

t r u m of t h e P t C L t " i o n c a n b e e v a l u a t e d f a i r l y a c c u r a t e l y i n solutions 2

w i t h h i g h c h l o r i d e concentrations. A s i m i l a r effect w a s e x p e c t e d for a s o l u t i o n of P t B r " at the c o r r e 4

2

s p o n d i n g b a n d w h i c h occurs at 24,400 c m " . H o w e v e r , i n s u c h a s o l u t i o n , 1


7.

M A R T I N

Ultraviolet

Spectroscopic

89

Qualities

as s h o w n i n F i g u r e 8, a l t h o u g h there was i n i t i a l l y a v e r y s m a l l decrease i n the a b s o r b a n c e , this decrease w a s f o l l o w e d b y a m u c h l a r g e r increase (27).

U p o n the a d d i t i o n of excess b r o m i d e i o n , the a b s o r b a n c e r e t u r n e d

to its i n i t i a l v a l u e w i t h a p e r i o d of a b o u t 5 m i n .

This behavior

was

a t t r i b u t e d to the f o r m a t i o n of the P t B r " d i m e r i c i o n i n t h e s o l u t i o n . 2

6

2

T h i s i o n h a d b e e n i d e n t i f i e d p r e v i o u s l y b y H a r r i s et al. ( 9 ) .

The data

i n F i g u r e 8 p r o v i d e d i n f o r m a t i o n a b o u t the rate of f o r m a t i o n a n d r e a c t i o n of this d i m e r . A p p a r e n t l y a n a q u a t i o n r e a c t i o n PtBr ~ + 4

H 0 -> P t B r ( H 0 ) - + B r ~

2

2

3

(4)

2

occurs i n i t i a l l y , b u t this process is f o l l o w e d b y the r e a c t i o n 2 P t B r ( H 0 ) - -> P t B r Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

3

2

2

2

6

- +

2H 0

(5)

2

T h i s d i m e r i c i o n c a n be c o n s i d e r e d i n e q u i l i b r i u m w i t h P t B r ~ i n a c c o r d 4

2

ance w i t h the r e a c t i o n 2 P t B r ~ P t B r 4

2

2

6

2

- +

2Br~

(6)

S i n c e i n the f o r m a t i o n of P t B r " f r o m P t B r ~ t w o b r o m i d e 2

6

2

4

2

ions

are

f o r m e d , there w i l l be a h i g h e r f r a c t i o n of the p l a t i n u m c o n v e r t e d to the d i m e r at h i g h e r d i l u t i o n . F i g u r e 9 illustrates the spectra r e c o r d e d i n a n e x p e r i m e n t i n w h i c h a s o l u t i o n of H P t B r 2

2

was diluted. T h e initial solu-

6

t i o n h a d b e e n f o r m e d b y p a s s i n g the t e t r a e t h y l a m m o n i u m salt of P t B r " 2

t h r o u g h a c a t i o n exchanger i n the h y d r o g e n phase.

6

2

U p o n d i l u t i o n , the

a b s o r b a n c e d e c r e a s e d t o w a r d a s p e c t r u m to be e x p e c t e d for the P t B r 3

( H 0 ) ~ i o n . W i t h the a d d i t i o n of excess K B r , the o b s e r v e d s p e c t r a c o i n 2

c i d e d w i t h that of P t B r " . 4

2

T h e o b s e r v e d s p e c t r a l changes i n d i c a t e d t h a t

the f o r m a t i o n of t h e d i m e r i c species, P t B r " , was too s l o w to a c c o u n t for 2

6

2

the i s o t o p i c exchange b e t w e e n free b r o m i d e i o n a n d the b r o m i d e l i g a n d s i n P t B r " , even t h o u g h the kinetics for s u c h e x c h a n g e i n c l u d e d a t e r m 4

2

w h i c h was s e c o n d o r d e r i n c o m p l e x . I t was c o n c l u d e d that s u c h e x c h a n g e o c c u r r e d t h r o u g h the m a k i n g a n d b r e a k i n g of s i n g l y

bromide-bridged

d i m e r i c complexes.

Spectra

in Organic

Media

A l t h o u g h t h e v i s i b l e a n d u l t r a v i o l e t spectra of the p l a t i n u m m e t a l c o m p l e x e s serve as a v a l u a b l e means to f o l l o w t h e i r reactions, this feature is e s p e c i a l l y d i s t u r b i n g to one w h o is t r y i n g to establish the e n e r g y states for a p a r t i c u l a r species.

S o m e care is necessary

to e s t a b l i s h that t h e

m e a s u r e d s p e c t r u m results f r o m the p a r t i c u l a r c o m p l e x species of interest, a n d not some of its r e a c t i o n p r o d u c t s .

W a t e r is a n effective n u c l e o p h i l e

for these complexes.

T o a v o i d s o l v a t i o n of some p l a t i n u m c o m p l e x e s ,

M a s o n a n d G r a y (21)

h a v e r e c e n t l y r e p o r t e d spectra of t h e t e t r a b u t y l -



PLATINUM

GROUP

METALS

AND

COMPOUNDS

Figure 9. Spectral changes when an aged solution of H Pt Br in a 1-cm cell (0 min) is diluted 10-fold and added to a 10-cm cell 2

2

6

Dashed curve obtained after the addition of solid KBr. Temp., 25°. NaN0 added to give ionic strength of 0.318M. 3

Figure 10. Spectrum of (NBu ) PtBr^ in a 2:1 mixture of 2-methyltetrahydrofuran and propionitrile at room temperature and at 77° Κ (liquid nitrogen) u 2


7.

MARTIN

Ultraviolet

Spectroscopic

a m m o n i u m tetrabromoplatinate (II)

91

Qualities

i n a n o r g a n i c solvent m e d i u m c o n

sisting of 2 : 1 m i x t u r e of 2 - m e t h y l t e t r a h y d r o f u r a n a n d p r o p i o n i t r i l e . I n this w a y s o l v a t i o n w a s a v o i d e d . I n a d d i t i o n , t h e y w e r e a b l e to c o o l these solutions as glasses to l i q u i d n i t r o g e n temperatures. T h i s p r o v i d e d m u c h better r e s o l u t i o n of t h e a b s o r p t i o n b a n d s , as is s h o w n i n t h e i r spectra i n F i g u r e 10. Shoulders at 26,500 a n d 33,000 c m the l o w e r temperatures.

- 1

are c l e a r l y r e s o l v e d at

S i n c e v i b r o n i c e x c i t a t i o n is r e d u c e d at l o w e r

temperatures, intensities of t h e s y m m e t r y - f o r b i d d e n b a n d s i n t h e r e g i o n of 20,000-30,000 c m '

1

are l o w e r at t h e l i q u i d n i t r o g e n temperatures. T h e

d i p o l e - a l l o w e d transitions, o n t h e other h a n d , possess a t e m p e r a t u r e i n d e p e n d e n t t o t a l i n t e n s i t y . T h e r e f o r e , as t h e b a n d s n a r r o w at l o w t e m


p e r a t u r e , e x t i n c t i o n coefficient peaks b e c o m e h i g h e r .

T h i s is e s p e c i a l l y

Ε ο vu >ι-

α ο (/)

ω

< < -J Ο

2

20000

25000 Z/cnrf

30000

35000

1

Figure 11. Absorption spectrum of Pt(en)Cl in an aqueous 0.3M Cl~ solution and in single crystals with polarized light at 300°Κ and at liquid helium tem peratures (nominally 15°K) 2


92

PLATINUM

GROUP

METALS

A N D COMPOUNDS

e v i d e n t i n t h e i r spectra f r o m 33,000-38,000 c m " , the r e g i o n o f the h i g h 1

i n t e n s i t y charge transfer b a n d s .

Spectrum of Diehlorο (ethylene diamine) platinum (II). Metal—Metal Interactions

Evidence for

W e h a v e r e c e n t l y o b t a i n e d some i n t e r e s t i n g spectra o f the n e u t r a l c o m p l e x P t ( e n ) C l . T h e s o l u t i o n s p e c t r u m of this c o m p l e x i n the r e g i o n 2

of the d-d b a n d s i s s h o w n i n F i g u r e 11. T h e charge transfer b a n d s are b e y o n d 48,000 c m " .

Its s o l u t i o n s p e c t r u m is v e r y s i m i l a r t o t h a t of

1

P t ( N H ) C l 2 , except t h a t the m o l a r a b s o r p t i v i t y i n the r e g i o n o f t h e 3

2

a b s o r p t i o n m a x i m u m is t w i c e as h i g h f o r the c i s - d i c h l o r o d i a m m i n e p l a t i -


num(II).

C h a t t , G a m l e n , a n d O r g e l ( 3 ) h a v e assigned the s p e c t r u m o f

t h e d i c h l o r o d i a m m i n e c o m p l e x o n t h e basis o f D

4 f e

symmetry, considering

the l i g a n d field d i s t o r t i o n t o b e a m i n o r effect. T h e p e a k at 33,000 c m " w a s assigned as the first s p i n - a l l o w e d d-d b a n d — i . e . , d

xy

b a n d for d , xz

yz

-> d* *. x

2

y

1

-» d* . . T h e 2

x

2

y

w a s c o n s i d e r e d the s h o u l d e r t o the h i g h energy

side o f this peak. T h e r e w e r e t h e n t w o f a i r l y w e l l r e s o l v a b l e s p i n - f o r b i d d e n b a n d s at l o n g e r w a v e l e n g t h s . T h e c r y s t a l s t r u c t u r e o f P t ( e n ) C l

2

was

recently determined b y x-ray diffraction methods b y Jacobson a n d Benson i n our laboratory ( I I ) .

T h e y f o u n d that the crystals b e l o n g e d

to t h e

o r t h o r h o m b i c system w i t h the molecules stacked i n a n e a r l y l i n e a r a r r a y , as s h o w n i n F i g u r e 12, w i t h a u n i f o r m s p a c i n g o f 3.39A b e t w e e n t h e

A

Β

Figure 12. A. Stacking of Pt(en)Cl molecules in the orthorhombic cry stab. B. Anticipated order of 1-electron orbital energies with their symmetry designations for the à-orbitals under the D and the C groups. 2

ih

2y


7.

MARTIN

Ultraviolet

p l a t i n u m atoms.

Spectroscopic

93

Qualities

T h i s s p a c i n g is o n l y 0.14A greater t h a n b e t w e e n t h e

ions i n M G S . V e r y t h i n crystals,
>

10 H z . C o n s e q u e n t l y , d e t e r m i n a t i o n

of the P M R s p e c t r u m suffices for the s t r u c t u r e assignment. c o u p l i n g s c h e m e has b e e n o b s e r v e d

A

similar

for o c t a h e d r a l i r i d i u m ( I I I )

com-

p o u n d s of the t y p e [ I r X Y ( P M e P h ) ] ( X a n d Y are u n i n e g a t i v e a n i o n s ) 2

2

3

(28). P r o t o n N M R has b e e n u s e d to s t u d y the g e o m e t r i c a l isomers of the 2,5-dithiahexane complexes [RhCl L ] 2

2

+

of R h C l

3

i n D 0 s o l u t i o n . C a t i o n i c species 2

are o b t a i n e d , a n d the trans a r r a n g e m e n t of c h l o r i d e s


assigned o n the basis of v i b r a t i o n a l spectra (58).

was

B e c a u s e of t h e possible

d i t h i a h e x a n e l i g a n d c o n f o r m a t i o n s , u p to five different isomers c a n exist w i t h trans c h l o r i d e s . doublets w i t h 1 0 3

3

/(

1 0 3

T h e p r o t o n resonance s p e c t r u m shows a series of

Rh- H) 1

=

1.05 H z .

B y i r r a d i a t i o n at t h e

proper

R h resonance f r e q u e n c y , the doublets c a n b e c o l l a p s e d one b y

g i v i n g the

1 0 3

R h c h e m i c a l shifts i n the different complexes

different species w e r e i d e n t i f i e d w i t h

1 0 3

(38).

one,

Seven

R h c h e m i c a l shifts over the r a n g e

0 - 2 9 6 p p m , i n d i c a t i n g t h a t some cis isomers also w e r e present. S t r u c t u r e X X I was assigned to the i s o m e r w i t h a shift of 38 p p m r e l a t i v e to t h e lowest

field

resonance,

m e t h y l resonances

because the s p e c t r u m

showed

three

different

w i t h one t w i c e the i n t e n s i t y of the other t w o , c o n -

sistent w i t h this geometry.

XXI

Solvation and Solvent Effects S o m e studies u s i n g oxygen-17 N M R spectroscopy w i t h aqueous ions.

solutions of p l a t i n u m ( I I )

have been

and organoplatinum ( I V )

M a n y years ago, it was r e p o r t e d t h a t treatment of

w i t h a n aqueous s o l u t i o n of A g N 0

3

or A g S 0 2

4

made cat-

PtCl (NH ) 2

2

2

gave c o n c e n t r a t e d s o l u -

tions of a species p r e s u m e d to b e the d i a q u o d i a m m i n e p l a t i n u m ( I I ) c a t i o n Solutions of the p e r c h l o r a t e salt s h o w a b o u n d w a t e r

oxygen-17

resonance s i g n a l 92.6 =t 1 p p m u p f i e l d f r o m the b u l k w a t e r

resonance

(30). (20).

T h i s l a r g e c h e m i c a l shift for the w a t e r b o u n d to p l a t i n u m m a y b e


110

PLATINUM

GROUP

METALS

AND

c o m p a r e d w i t h t h e v a l u e of ca. —11 p p m for A 1 ( C 1 0 ) 4

COMPOUNDS

solutions

3

(9).

T h e r e w a s n o c h a n g e i n the c h e m i c a l shift over the t e m p e r a t u r e r a n g e 29° to 8 5 ° , i n d i c a t i n g that the w a t e r is r e l a t i v e l y i n e r t to s u b s t i t u t i o n . I n t e g r a t i o n of the b o u n d a n d b u l k w a t e r resonances gave the h y d r a t i o n number

as 1.9

±

[(H N)2Pt(OH )2] 3

2

0.1, c o n f i r m i n g the f o r m u l a t i o n of 2 +

.

the

cation

as

U n d o u b t e d l y , this c a t i o n is sufficiently i n e r t t h a t

the s o l v a t i o n n u m b e r c o u l d be d e t e r m i n e d b y conventional—e.g.,

isotope

dilution—techniques. T h e h y d r a t i o n of the t r i m e t h y l p l a t i n u m c a t i o n also has b e e n s t u d i e d by

1 7

0 N M R of aqueous solutions of ( C H ) P t C 1 0 3

3

4

Although

(20, 21).

m a n y p l a t i n u m ( I V ) complexes are n u m b e r e d a m o n g the most i n e r t co o r d i n a t i o n c o m p o u n d s k n o w n , the w a t e r molepules b o u n d to ( C H ) P t 3


exchange r a p i d l y w i t h the b u l k solvent at r o o m t e m p e r a t u r e . 0 ° C is i t possible to r e c o r d a b o u n d w a t e r resonance.

3

+

O n l y near

E m p l o y i n g the

m o l a l shift of the b u l k w a t e r solvent c a u s e d b y a d d e d D y ( C 1 0 ) , i t w a s 4

possible to d e t e r m i n e the h y d r a t i o n n u m b e r to b e 3.0 ±

is f o r m u l a t e d c o r r e c t l y as o c t a h e d r a l [ ( C H ) P t ( O H ) ] . 3

the l a r g e q u a d r u p o l e m o m e n t of the w i t h the

1 9 5

3

0 nucleus, 1 =

1 7

2

3

0.1. T h e c a t i o n 3

Because

+

of

5/2, no coupling

P t n u c l e u s w a s detected i n a n y of the spectra d e s c r i b e d above.

T h e s e experiments i l l u s t r a t e the v e r y great l a b i l i t y of some of the organo d e r i v a t i v e s of the p l a t i n u m g r o u p metals. C l e g g and H a l l (8)

n o t e d that the a d d i t i o n of s u l f u r i c a c i d to a n

aqueous s o l u t i o n of [ ( C H ) P t ( N H ) ] C l caused a shift of 0.5 p p m i n 3

3

3

3

the m e t h y l p r o t o n resonance a n d a n increase i n the v a l u e of / ( 2

1 9 5

Pt-CH ) 3

f r o m 71.0 to 79.7 H z because of r a p i d f o r m a t i o n of the t r i a q u o species. A d d i t i o n of a n excess of the l i g a n d s H C N H , p y r i d i n e , S C N " , N 0 " , a n d 3

2

C N " a l l gave rise to spectra c h a r a c t e r i s t i c of the c o m p l e x e d platinum ( I V ) cation

2

trimethyl

(7).

S a w y e r a n d c o w o r k e r s have s t u d i e d the p r o t o n resonance s p e c t r a of aqueous solutions of the 1:1 a n d 1:2 complexes f o r m e d f r o m P t ( I I ) Pd(II)

(53),

and Rh(III)

(52)

(51),

w i t h nitrilotriacetic acid, N - m e t h y l -

i m i n o d i a c e t i c a c i d , a n d i m i n o d i a c e t i c a c i d as a f u n c t i o n b o t h of

tem

p e r a t u r e a n d of p H . T h e acetate m e t h y l e n e protons e x h i b i t a n A B p a t t e r n i n a l l of the complexes, i n d i c a t i n g that the lifetimes of m e t a l - o x y g e n a n d m e t a l - n i t r o g e n b o n d s are r e l a t i v e l y long—i.e., that the

complexes

are s t e r e o c h e m i c a l ^ r i g i d . B o t h the m o n o X X I I a n d bis X X I I I

complexes

of p l a t i n u m ( I I )

show

1 9 5

Ρ ί - Ή c o u p l i n g s t h r o u g h three b o n d s to

the

acetate m e t h y l e n e protons a n d to the N - s u b s t i t u t e d groups. N o analogous c o u p l i n g s w e r e f o u n d w i t h the R h ( I I I ) chelates. C o m p l e x changes as the p H is r a i s e d w i t h the c o n c o m i t a n t f o r m a t i o n of h y d r o x o a n d p r o b a b l y p o l y n u c l e a r species.

occur

complexes

T h e s e changes c a n b e f o l l o w e d

con

v e n i e n t l y w i t h the p r o t o n resonance spectra, a l t h o u g h a d e t a i l e d i n t e r p r e t a t i o n of the effects is v e r y difficult.


8.

TOBIAS

NMR

Spectra

of

111

Compounds

E M

2XHI

T h e i n t e r a c t i o n of cations f o r m e d f r o m the p l a t i n u m g r o u p metals Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

w i t h solvents l i k e a c e t o n i t r i l e , d i m e t h y l s u l f o x i d e , a n d other c o n t a i n i n g m e t h y l protons is s t u d i e d easily w i t h Ή complexes

are r a t h e r inert. O ' B r i e n , G l a s s , a n d R e y n o l d s

m i n e d the s o l v a t i o n n u m b e r of ( H N ) P t 3

2

2 +

molecules

N M R , since these deter

(42)

i n acetonitrile solution from

the p r o t o n resonance spectra of solutions of a n h y d r o u s ( H N ) P t ( C 1 0 ) . 3

2

4

2

B o t h b o u n d a n d b u l k a c e t o n i t r i l e resonances w e r e o b s e r v e d w i t h n o e v i d e n c e for a n y exchange b r o a d e n i n g to 8 1 ° , the b o i l i n g p o i n t of aceto n i t r i l e . C o u p l i n g of the l i g a n d protons w i t h the p l a t i n u m n u c l e u s leads to the u s u a l 1:4:1 t r i p l e t , / ( 4

1 9 5

Ρί-Ή)

=

12.1 H z . I n t e g r a t i o n of

c o m p o n e n t of the t r i p l e t for the b o u n d solvent r e l a t i v e to the b a n d of the b u l k solvent gave a s o l v a t i o n n u m b e r of 2.0 ±

1 3

one

C side

0.1. It also

was possible to d e t e r m i n e a p p r o x i m a t e l y the r e l a t i v e integrals of

the

amine and

are

a c e t o n i t r i l e protons,

v e r y b r o a d because of the

1 4

a l t h o u g h the

a m i n e resonances

N quadrupole moment.

a s o l v a t i o n n u m b e r of 2.0 =b 0.1, too.

T h i s m e t h o d gives

T h e r e was no shift i n the b u l k

solvent resonance as the c o n c e n t r a t i o n of [ ( H N ) P t ( N C C H ) ] ( C 1 0 ) 3

2

3

2

4

2

was v a r i e d , suggesting that there are no significant solvent interactions i n the a x i a l positions of p l a t i n u m . Anhydrous ( H N ) P t ( C 1 0 ) 3

3

4

2

also has b e e n s t u d i e d i n d i m e t h y l s u l f

oxide s o l u t i o n ( 5 5 ) , since M e S O is a n a m b i d e n t a t e l i g a n d a n d p r o b a b l y 2

coordinates via s u l f u r r a t h e r t h a n o x y g e n as is k n o w n to b e the case w i t h p a l l a d i u m . T h e m e t h y l p r o t o n resonance for the b o u n d D M S O is s h i f t e d 2.54 p p m u p f i e l d f r o m the b u l k solvent, a n d the l i g a n d exchange rate is n e g l i g i b l e at 3 5 ° . the b o u n d D M S O n u m b e r s of 2.0 ±

Integrations of the b u l k a n d b o u n d D M S O signals or a n d a m i n e p r o t o n resonances 0.1. T h e c o u p l i n g constant / (

1 9 5

b o t h gave s o l v a t i o n Ρΐ-Ή)

=

23.2 H z ,

a n d this l a r g e a v a l u e suggests that D M S O is b o u n d via s u l f u r a n d n o t oxygen—i.e., t h a t the c o u p l i n g is t h r o u g h o n l y three a n d n o t f o u r b o n d s . U n d o u b t e d l y , i s o l a t i o n of the c r y s t a l l i n e a d d u c t s ( H N ) P t ( C 1 0 ) 3

2

4

2

· 2B

f r o m s o l u t i o n w o u l d c o n f i r m these s t o i c h i o m e t r i c s ; h o w e v e r , these c o m p o u n d s are v e r y explosive.


112

PLATINUM

M c F a r l a n e and W h i t e (37)

GROUP

METALS

2

COMPOUNDS

h a v e n o t e d that d i m e t h y l s u l f o x i d e w i l l

replace M e S and M e S e w h e n [ ( M e L ) P t C l ] ( L = 2

AND

2

2

S, S e )

2

complexes

are d i s s o l v e d i n D M S O a c c o r d i n g to R e a c t i o n s 4 a n d 5. (Me L) PtCl 2

2

+

2

D M S O )

άω =

1


ο If t h e lattice is a s s u m e d to h a v e a D e b y e f r e q u e n c y s p e c t r u m w i t h c o = k6 /h, then DW

m

where 6

DW

is t h e effective D e b y e t e m p e r a t u r e .

s p e c t r u m , G (ω),

Since t h e r e a l f r e q u e n c y

m a y b e c o n s i d e r a b l y different f r o m a h a r m o n i c

Debye

s p e c t r u m , t h e effective D e b y e t e m p e r a t u r e a p p r o p r i a t e to a n y other q u a n t i t y i n v o l v i n g a different average over t h e s p e c t r u m m a y b e a p p r e c i a b l y different f r o m 6 DW

T h u s , for example, the D e b y e temperature 0 perti C

nent to the heat c a p a c i t y w i l l v a r y m u c h m o r e r a p i d l y w i t h t e m p e r a t u r e than 0 . DW

I n p r i n c i p l e , h o w e v e r , f r o m k n o w l e d g e of t h e heat c a p a c i t y ,

lattice constants, a n d elastic constants as a f u n c t i o n of t e m p e r a t u r e , one c a n l e a r n e n o u g h a b o u t the f r e q u e n c y s p e c t r u m to p r e d i c t t h e D e b y e W a l l e r factor.

F e l d m a n a n d H o r t o n ( 7 ) have m a d e s u c h a c a l c u l a t i o n

in the quasiharmonic approximation i n w h i c h the lattice potential i n P t m e t a l is a s s u m e d to b e h a r m o n i c , a n d of a l l a n h a r m o n i c effects, o n l y the

_ 240

^23I°K

229 K>^ e

Ξ 230 ο ®

225 K^^ e

220 210 0

100

50

150

200

250

300 Physical Review

Figure 4. Flot of ^ ( T ) vs. T . The solid line gives the value of ^ D W ( T ) referred to the 0°K volume. The broken line shows the effect of thermal expansion ( 7 ) . D

W


140

PLATINUM

t h e r m a l expansion is t a k e n i n t o account. D e b y e temperature should b e 0

DW

=

GROUP

METALS

A N D COMPOUNDS

T h e i r conclusions are that the

(231 ± 3 ) ° K at 0 ° K a n d s h o u l d

have a very slight temperature dependence ( F i g u r e 4 ) . Experimentally, f r o m the analysis of the t e m p e r a t u r e d e p e n d e n c e of the a b s o r p t i o n s p e c t r a o b t a i n e d w i t h a source o f

1 9 5

A u embedded in a natural platinum matrix

a n d a n a t u r a l p l a t i n u m absorber, H a r r i s , R o t h b e r g , a n d B e n c z e r - K o l l e r (JO) obtained an extrapolated 0

DW

=

(234 ± 6 ) ° K at 0 ° K i n excellent

a g r e e m e n t w i t h t h e o r e t i c a l p r e d i c t i o n s f o r the p l a t i n u m c u b i c l a t t i c e . A c t u a l l y , the q u a n t i t y t h a t is m e a s u r e d is f/(l

+ a), n a m e l y a c o m b i n a

t i o n o f the recoilless f r a c t i o n / a n d o f the c o n v e r s i o n coefficient « . T h e determination of 6

DW

is t h e n v e r y sensitive to the c h o i c e o f a ( F i g u r e 5 ) .

If the e x p e r i m e n t a l 2 W is fitted to the t h e o r e t i c a l p r e d i c t i o n s o f F e l d m a n Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

a n d H o r t o n , t h e n a v a l u e for the c o n v e r s i o n coefficient a c a n b e o b t a i n e d , a = 7.0 ± 0.3. T h i s v a l u e o f the i n t e r n a l c o n v e r s i o n coefficient is m o r e

β no

K)

2030405060708090100 TfK) Physical Review

Figure 5. Experimental values ( 9 ) of 0 for various values of the internal conversion coefficient vs. temperature. The solid line was obtained from the analysis of specific heat measurements and other thermody namic data ( 7 ) . D W


B E N C Z E R - K O L L E R

Survey of Mossbauer

141

Spectroscopy


10.

Physics Letters

Figure 6.

Mossbauer spectra with Pt in ferromagnetic

alloys


(2)

142

GROUP

METALS

AND

COMPOUNDS


PLATINUM

Physical Review

Figure

7. Mossbauer spectra for Pt-Fe absorbers in different field configurations (1)



10.

BENCZER-KOLLER

Survey of Mossbauer

143

Spectroscopy

Physical Review

Figure 8. Mossbauer spectra for absorbers of Pt-Co, Pt-Ni, and Pt (1) precise t h a n t h a t w h i c h c a n b e o b t a i n e d b y a n y of the n u c l e a r spectroscopy m e t h o d s a v a i l a b l e to date.

Hyperfine Interaction T h e M o s s b a u e r a b s o r p t i o n of scattering experiments w e r e c a r r i e d out b y B e n c z e r - K o l l e r , H a r r i s , a n d R o t h b e r g ( 3 ) , A t a c , D e b r u n n e r , a n d F r a u e n f e l d e r (2),

Agresti, Kankeleit, a n d Persson ( J ) , a n d B u y r n , G r o d -

zins, B l u m , a n d W u l f f (6) Pt-Fe

w i t h a single l i n e source a n d absorbers

alloys r a n g i n g i n c o m p o s i t i o n

from

P t - C o , a n d P t - N i alloys as w e l l as P t F e . 3

Pto.03Feo.97 to

of

Pt .5oFe .5o, 0

0

A t y p i c a l s p e c t r u m is s h o w n

i n F i g u r e 6. T h e e x p e c t e d 6-line p a t t e r n c o r r e s p o n d i n g to a 3 / 2 - »

1/2

m a g n e t i c d i p o l e t r a n s i t i o n is not r e s o l v e d , a n d o n l y t w o peaks c a n b e o b served. F r o m a 6-line fit to the o b s e r v e d p a t t e r n , H a r r i s et al. ( 3 )


were

144

PLATINUM

Table I.

GROUP

AND

COMPOUNDS

Magnetic Moment of the 99 k e V Excited State in T.,

Absorber

°K

T.,

°K

Pto.iFeo.9 Pt Fe

229 418

20 20

20 20

Pto.sFeo.7 Pto.07Coo.93 Pto.07Nio.93

166 71.5 140

29 29 29

29 29 29

Pto.03Feo.97 Pto.03Coo.97 Pto.03Nio.97

30-60 50 50

4.2 4.2 4.2

4.2 4.2 4.2

Pto.03Feo.97 •

52

4.2

4.2

3


METALS

• 521

Pto.50Feo.50

Calorimetric determination P o l a r i z e d n e u t r o n - s p i n resonance

Pto.03Feo.97 Pto.iFeo.9 Average

Table II.

W i d t h , Isomer Shift, Magnitude of the A u in Various Matrices and 1 9 5

(Mv\

t Source Matrix

\Cm2J

Pt

Cu Be Ir Pt 195mp

t

p

m

t

T.,

°K

Foil

326 326 610 104

4.2 4.2 4.2 20.0

4.2 4.2 4.2 20.0

326

4.2

4.2

o n l y a b l e to o b t a i n a r e l a t i o n s h i p b e t w e e n H n u c l e u s , a n d the r a t i o μ*/μ

ΰ

i n t

2.04 ± 0.10 ~2.5 3.05 ± 0.15 2.1 =fc 0.2

, t h e effective field at the

of m a g n e t i c m o m e n t s

of the e x c i t e d

and

g r o u n d states. T h e three o t h e r groups a l t e r e d t h e a b s o r p t i o n or s c a t t e r i n g patterns b y p o l a r i z i n g t h e absorbers w i t h a n e x t e r n a l field a p p l i e d e i t h e r p a r a l l e l or p e r p e n d i c u l a r to the g a m m a r a y e m i s s i o n ( F i g u r e s 7 a n d 8 ) . T h e y thus w e r e able to o b t a i n u n i q u e v a l u e s for the s i g n a n d m a g n i t u d e of μβ a n d H

i n t

.

T h e s e results, as w e l l as i n t e r n a l fields o b t a i n e d f r o m a

c a l o r i m e t r i c d e t e r m i n a t i o n (11)

a n d a p o l a r i z e d n e u t r o n s p i n resonance


10. 1 9 5

Spectroscopy

145

P t and Internal Magnetic Field for Various P t - F e Alloys

μ


Survey of Mossbauer

B E N C Z E R - K O L L E R

Hint MG

β

Ref.

-0.9 iridium) established (2) for 150 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

11.

Double

R Y L A N D E R

Bond

151

Isomerization

1-pentene, for the t e n d e n c y to p r o m o t e d o u b l e b o n d m i g r a t i o n d u r i n g hydrogénation, is p r o b a b l y g e n e r a l for most olefinic systems.

T h e extent

of i s o m e r i z a t i o n also d e p e n d s i m p o r t a n t l y o n t h e substrate.

For migra-

t i o n to occur, the a l l y l i c h y d r o g e n

to b e r e m o v e d

m u s t be

sterically

accessible to the catalyst a n d o n the same side of the m o l e c u l e as t h e entering hydrogen ( 5 ) .

T h e m e c h a n i s m i n v o l v e d m a y be c o m p l e x

M i g r a t i o n is d i m i n i s h e d b y the presence of h e a v y metals, amines, a n d e l e v a t e d pressure Selectivity

Among

Olefinic

(3).

hydroxides,

(15). Types

A u s e f u l g e n e r a l i t y i n p r e d i c t i n g selectivity is that the rate of h y d r o -


génation falls, b o t h a b s o l u t e l y a n d c o m p e t i t i v e l y , as steric a r o u n d the d o u b l e b o n d is i n c r e a s e d (23).

hinderance

O n this basis i n a m i x t u r e of

olefins, t e r m i n a l olefins w o u l d b e e x p e c t e d to be s a t u r a t e d p r e f e r e n t i a l l y to i n t e r n a l olefins, i f a p r i o r r a p i d e q u i l i b r a t i o n b y i s o m e r i z a t i o n d i d not ensue. T h i s thesis was d e m o n s t r a t e d the pairs of

olefins

shown

(1)

in Table

i n the selective hydrogénation of I, over r u t h e n i u m - o n - c a r b o n ,

a

catalyst w i t h r e l a t i v e l y l o w i s o m e r i z a t i o n a c t i v i t y . T h e experiments

were

c a r r i e d out b y p a r t i a l hydrogénation of a m i x t u r e of 1 m o l e of

each

olefin, a n d the r e a c t i o n was i n t e r r u p t e d a n d a n a l y z e d after of 1 m o l e of h y d r o g e n .

absorption

Those compounds underlined i n Table I were

r e d u c e d w i t h h i g h s e l e c t i v i t y i n preference

to the other m e m b e r of the

p a i r . T h i s h i g h degree of selectivity w a s l i m i t e d to those pairs of olefins

Table I.

Competitive Hydrogénation of Olefins by Ruthenium on Carbon 2-methyl-2-pentene

Selective

a n d 2 - m e t h y l - 1-pentene a n d 2-octene a n d cyclohexene and 2-methyl-1-pentene

Selective Selective

4-Methyl-1-pentene and 4-Methyl-l-pentene 4-Methyl-l-pentene 4-Methyl-l-pentene 2-Methyl-2-pentene

2 - M e t h y l - 2 - p e n t e n e a n d 2-octene 2 - M e t h y l - 2 - p e n t e n e a n d 1-octene 2 - M e t h y l - 2 - p e n t e n e a n d cyclohexene 2 - M e t h y l - l - p e n t e n e a n d 2-octene 2 - M e t h y l - l - p e n t e n e a n d 1-octene 2 - M e t h y l - l - p e n t e n e a n d cyclohexene 2-Octene a n d 1-octene 2-Octene a n d cyclohexene 1-Octene a n d cyclohexene

Selective N o t selective N o t selective Selective N o t selective N o t selective Selective N o t selective Selective N o t selective Selective


152

PLATINUM

GROUP

METALS

AND

COMPOUNDS

c o n t a i n i n g one t e r m i n a l a n d one i n t e r n a l olefin; other pairs w e r e r e d u c e d w i t h a m u c h l o w e r selectivity. T h i s same t y p e of d i s c r i m i n a t i o n b e t w e e n i n t e r n a l a n d t e r m i n a l olefins also has b e e n d e m o n s t r a t e d w h e n the t w o types of d o u b l e b o n d s w e r e i n the same m o l e c u l e . T h e s e hydrogénations w e r e c a r r i e d out w i t h w a t e r as a solvent, i f i n d e e d solvent is the correct w o r d to use w i t h olefins, b u t i f there w e r e no w a t e r present there w a s n o r e d u c t i o n . T h i s is a c o m m o n c h a r a c t e r i s t i c of r u t h e n i u m catalysis at l o w pressure. A t h i g h pressure, m a n y solvents c a n be u s e d , b u t e v e n here w a t e r sometimes has a s t r i k i n g l y b e n e f i c i a l effect o n the rate ( 3 2 ) . S e l e c t i v i t y of the t y p e f o u n d w i t h r u t h e n i u m w a s not possible w h e n p a l l a d i u m catalysts w e r e u s e d . F o r instance, hydrogénation of a m i x t u r e of 1- a n d 2-octene was c o m p l e t e l y nonselective over p a l l a d i u m catalysts. Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

T h i s l a c k of s e l e c t i v i t y r e s u l t e d f r o m the h i g h i s o m e r i z a t i o n a c t i v i t y of p a l l a d i u m ; w h e n the r e a c t i o n w a s s t o p p e d at o n l y one-tenth of

comple-

t i o n , a l l 1-octene h a d d i s a p p e a r e d b y m i g r a t i o n of the t e r m i n a l d o u b l e bond inward.

Migration to Inaccessible Positions T r i v i a l r e d u c t i o n s at times m a y b e r e n d e r e d difficult or i m p o s s i b l e b y i m p r o p e r selection of catalysts. T h i s is d e m o n s t r a t e d

(13)

b y the

hydrogénation of p u l c h e l l i n , I. O v e r p l a t i n u m oxide i n e t h a n o l , p u l c h e l l i n w a s r e d u c e d to d i h y d r o p u l c h e l l i n , I I . O n the other h a n d , r e d u c t i o n of p u l c h e l l i n over p a l l a d i u m - o n - c a r b o n or p a l l a d i u m - o n - c a l c i u m c a r b o n a t e afforded d i h y d r o p u l c h e l l i n i n 6 0 - 8 0 % y i e l d a c c o m p a n i e d b y the i s o m e r i z e d p r o d u c t , i s o p u l c h e l l i n , I I I . T h e s e results are i n k e e p i n g w i t h the greater t e n d e n c y of p a l l a d i u m to cause d o u b l e b o n d m i g r a t i o n . It w o u l d b e most difficult to convert i s o p u l c h e l l i n to d i h y d r o p u l c h e l l i n b y c a t a l y t i c hydrogénation, f o r a n y a t t e m p t to d o so p r o b a b l y w o u l d result i n h y d r o genolysis of the a l l y l i c c a r b o n - o x y g e n b o n d .


11.

Double

R Y L A N D E R

Bond

153

Isomerization

T h e r e are m a n y other examples of d o u b l e b o n d m i g r a t i o n to a t e t r a s u b s t i t u t e d p o s i t i o n , a n d these i n c l u d e hydrogénations e v e n over p l a t i n u m , a catalyst w i t h a r e l a t i v e l y l o w i s o m e r i z a t i o n a c t i v i t y (24).

One

example, the a t t e m p t e d hydrogénation of the e x o c y c l i c d o u b l e b o n d of h y s t e r i n o v e r p l a t i n u m oxide, r e s u l t e d i n i s o m e r i z a t i o n to i s o h y s t e r i n , w h i c h w a s resistant to hydrogénation u n d e r the c o n d i t i o n s of the r e a c t i o n . H y s t e r i n (39)

w a s r e d u c e d successfully over r u t h e n i u m d i o x i d e at ele-

v a t e d temperatures a n d pressures. It is e x p e c t e d that the e l e v a t e d p r e s sures u s e d w i t h r u t h e n i u m w o u l d d i m i n i s h i s o m e r i z a t i o n , a n d t h e v i g o r o u s c o n d i t i o n s w i t h r u t h e n i u m also m i g h t be sufficient to r e d u c e i s o h y s t e r i n if i t f o r m e d .


Changes

in the Organic

Function

I s o m e r i z a t i o n d u r i n g hydrogénation m a y a l t e r the f u n c t i o n a l g r o u p s present i n the m o l e c u l e . 5%

F o r instance, r e d u c t i o n of c y c l o h e x e n - 2 - o l

over

p l a t i n u m - o n - c a r b o n o c c u r r e d w i t h r a p i d a b s o r p t i o n of 1 m o l e

of

h y d r o g e n at s u b s t a n t i a l l y constant rate a n d q u a n t i t a t i v e f o r m a t i o n of cyclohexanol.

O n t h e other h a n d , r e d u c t i o n over p a l l a d i u m ceased

ab-

r u p t l y at about t w o - t h i r d s of a m o l e , a n d the p r o d u c t w a s a m i x t u r e of c y c l o h e x a n o l a n d c y c l o h e x a n o n e , the latter a r i s i n g t h r o u g h d o u b l e b o n d m i g r a t i o n to the e n o l of c y c l o h e x a n o n e OH

Λ,

(29). OH

Ο

Λ

Λ,

5% P d / C

67%

33%

5% P t / C

100%

0%

T h i s t y p e of t r a n s f o r m a t i o n m a y o c c u r also b y a n exchange r e a c t i o n . C a t a l y t i c hydrogénation of

5-cyclodecen-l-ol

over

p l a t i n u m oxide

m e t h a n o l r e s u l t e d i n a b s o r p t i o n of 0.97 m o l a r e q u i v a l e n t s of

in

hydrogen

a n d f o r m a t i o n of the s a t u r a t e d a l c o h o l . H o w e v e r , w h e n 1 0 % p a l l a d i u m o n - c a r b o n i n a l c o h o l was u s e d as a catalyst, r e d u c t i o n w a s i n c o m p l e t e o w i n g to f o r m a t i o n of c y c l o d e c a n o n e .

T h e authors (8)

e x p l a i n e d the

e x c e p t i o n a l ease o f this t y p e of r e a c t i o n b y the s p a t i a l p r o x i m i t y of t h e a l c o h o l a n d olefin g r o u p s , f a v o r i n g a n i n t r a m o l e c u l a r h y d r o g e n transfer. P r e s u m a b l y , p a l l a d i u m is v e r y m u c h m o r e effective i n this transfer r e a c t i o n t h a n p l a t i n u m , b u t s i m i l a r transfer b y p l a t i n u m m i g h t pass u n o b s e r v e d , as this catalyst w o u l d r e d u c e the ketone so f o r m e d to a l c o h o l ; p a l l a d i u m is a r e l a t i v e l y p o o r catalyst for hydrogénation a l i p h a t i c ketones

(6).


the of

154

PLATINUM

GROUP

METALS

AND

COMPOUNDS

OH

OH


Catalyst

Inhibition

W i t h sufficient use, a l l catalysts u n d e r g o d e a c t i v a t i o n .

Two

broad

types of i n h i b i t i o n m a y be d i s t i n g u i s h e d . I n the first, the catalyst b e comes i n h i b i t e d t h r o u g h the i n t r o d u c t i o n of catalyst i n h i b i t o r s c a r r i e d i n t o the system b y the substrate, solvent, h y d r o g e n , o r e v e n f o r m e d

by

d i s s o l u t i o n of the reactor. I n the second t y p e , d e a c t i v a t i o n arises t h r o u g h some i n h i b i t o r f o r m e d i n the r e a c t i o n itself. A n e x a m p l e of the t y p e is p r o v i d e d b y the w o r k of N i s h i m u r a a n d H a m a (21).

second

These work-

ers f o u n d , c o n t r a r y to w h a t one m i g h t expect b y a n a l o g y to s i m i l a r s i t u a tions, that b e n z y l a l c o h o l w a s r e d u c e d m o r e s m o o t h l y to c y c l o h e x y l c a r b i n o l over

p l a t i n u m oxide

t h a n over

r h o d i u m catalysts.

The

rate

of

hydrogénation over r h o d i u m decreased m a r k e d l y d u r i n g the course

of

the r e a c t i o n , a c c o m p a n i e d

b y the f o r m a t i o n of i n c r e a s i n g amounts

of

cyclohexanecarboxaldehyde,

a strong i n h i b i t o r . R e d u c t i o n s over p l a t i n u m

catalyst, o n the other h a n d , p r o c e e d e d at a m o r e n e a r l y constant rate a n d w i t h the a c c u m u l a t i o n of less a l d e h y d e .

The inhibiting

b o x a l d e h y d e arose f r o m i s o m e r i z a t i o n of i n t e r m e d i a t e

cyclohexanecar-

1-cyclohexenylcar-

b i n o l . P l a t i n u m catalysts w e r e less i n h i b i t e d t h a n r h o d i u m b y t h e a l d e h y d e o n t w o counts.

T h e i n t e r m e d i a t e u n s a t u r a t e d c a r b i n o l w a s isomer-

i z e d less over p l a t i n u m t h a n r h o d i u m , a n d the a l d e h y d e once f o r m e d w a s h y d r o g e n a t e d a b o u t four to five times m o r e r a p i d l y over p l a t i n u m .

CH OH 2

CH OH 2

CHO

S i m i l a r isomerizations h a v e been o b s e r v e d i n the hydrogénation of p h e n y l e t h a n o l over r h o d i u m , w h e r e one of the i n t e r m e d i a t e p r o d u c t s is cyclohexylmethylketone.


11.

R Y L A N D E R

Double

Bond

155

Isomerization

T h i s ketone, u n l i k e c y c l o h e x a n e c a r b o x a l d e h y d e ,

is not a n i n h i b i t o r a n d

c a n b e o b t a i n e d as a n i n t e r m e d i a t e i n about 4 0 % y i e l d f r o m hydrogénat i o n of a c e t o p h e n o n e over r h o d i u m ; f u r t h e r r e d u c t i o n affords h i g h y i e l d s of c y c l o h e x y l m e t h y l c a r b i n o l

(28).

Hydrogenolysis of Carbon-Oxygen Bonds C a r b o n - o x y g e n b o n d s are not c l e a v e d r e a d i l y b y c a t a l y t i c h y d r o genolysis unless t h e y are i n some w a y a c t i v a t e d b y p r o x i m i t y to another function.

Benzylic, vinylic, and allylic oxygen bonds undergo a facile

h y d r o g e n o l y s i s , b u t f u n c t i o n s r e m o v e d f r o m the d o u b l e unless a p r i o r i s o m e r i z a t i o n occurs.

b o n d do

not

A n e x a m p l e of i s o m e r i z a t i o n l e a d i n g


to h y d r o g e n o l y s i s p r o d u c t s is f o u n d i n the hydrogénation of h e p t - 3 - y n e 1,7-diol over 5 % p a l l a d i u m - o n - b a r i u m sulfate; i n a d d i t i o n to t h e expected d i o l , a c o n s i d e r a b l e a m o u n t of 1-heptanol w a s f o r m e d ( 9 ) .

The forma-

t i o n of 1-heptanol is best a c c o u n t e d for b y the a s s u m p t i o n of r e d u c t i o n of the acetylene to the c o r r e s p o n d i n g olefin f o l l o w e d b y i s o m e r i z a t i o n of the d o u b l e b o n d i n t o a n a l l y l i c p o s i t i o n .

P l a t i n u m , or better r h o d i u m ,

w o u l d b e p r e f e r r e d to p a l l a d i u m i n examples of this t y p e .

Rhodium

w o u l d seem p a r t i c u l a r l y d e s i r a b l e o n t w o counts. T h e i s o m e r i z a t i o n a c t i v i t y of r h o d i u m is m u c h l o w e r t h a n that of p a l l a d i u m , a n d less a l l y l i c a l c o h o l w o u l d be f o r m e d i n the hydrogénation. A d d i t i o n a l l y , r h o d i u m has f o u n d c o n s i d e r a b l e use i n the r e d u c t i o n of a l l y l i c a n d v i n y l i c systems w h e n h y d r o g e n o l y s i s was to be a v o i d e d

(27).

H O C H C H C = C C H C H C H O H -> 2

2

2

2

2

HOCH CH CH = CHCH CH CH OH

->

HOCH CH = CHCH CH CH CH OH

-*

2

2

2

2

2

2

2

2

2

2

CH CH = CHCH CH CH CH OH 3

2

2

2

2

->

CH3CH CH CH CH CH CH OH 2

2

2

2

2

2

Hydrogenolysis of Carbon-Carbon Bonds A s t r i k i n g e x a m p l e of the effect i s o m e r i z a t i o n m a y h a v e is f o u n d i n the hydrogénation of car-3-ene ( 7 ) .

T w o different p r o d u c t s are o b t a i n e d

i n nearly quantitative yield, depending p l a t i n u m - o n - c a r b o n at 1500 p s i g , cis-carane

on

the

catalyst u s e d .

Over

was obtained i n 9 8 % y i e l d ,

whereas over p a l l a d i u m - o n - c a r b o n , q u a n t i t a t i v e y i e l d s of 1,1,4-trimethylcycloheptane could be achieved.

H y d r o g e n o l y s i s w i t h f o r m a t i o n of the

s e v e n - m e m b e r e d r i n g s w a s b e l i e v e d to be p r e c e e d e d b y i s o m e r i z a t i o n to car-2-ene.

If i s o m e r i z a t i o n is a p r e r e q u i s i t e for h y d r o g e n o l y s i s , i t is to b e

e x p e c t e d that less of the h y d r o g e n o l y s i s p r o d u c t w o u l d b e f o r m e d


over

156

PLATINUM

GROUP

METALS

AND

COMPOUNDS

p l a t i n u m , since p l a t i n u m is n o t as a c t i v e as p a l l a d i u m for d o u b l e b o n d


migration.

F o r m a t i o n of 1,1,4-trimethylcycloheptane f r o m car-3-ene d e p e n d s o n t w o properties of p a l l a d i u m , the strong t e n d e n c y of p a l l a d i u m to p r o m o t e i s o m e r i z a t i o n a n d to h y d r o g e n o l y z e v i n y l c y c l o p r o p a n e systems.

I n the

b i c y c l i c u n s a t u r a t e d a c i d , I V , p r i o r i s o m e r i z a t i o n is not necessary

to

m o v e the d o u b l e b o n d i n t o c o n j u g a t i o n , yet here, too, p l a t i n u m a n d p a l l a d i u m g i v e q u i t e different results. T h e s a t u r a t e d b i c y c l i c a c i d is f o r m e d over p l a t i n u m , w h e r e a s over p a l l a d i u m a m i x t u r e of c y c l o h e x a n e carboxylic acid and benzoic disproportionation

COOH

a c i d results t h r o u g h h y d r o g e n o l y s i s a n d

(20).

COOH

COOH

COOH

Disproportionation D i s p r o p o r t i o n a t i o n is a s p e c i a l f o r m of d o u b l e b o n d m i g r a t i o n i n w h i c h the d o u b l e b o n d is t r a n s f e r r e d f r o m one m o l e c u l e to another. R e a c t i o n s of this t y p e are e s p e c i a l l y l i a b l e to o c c u r over p a l l a d i u m , a n d for this reason p a l l a d i u m sometimes is best a v o i d e d i n olefin hydrogénat i o n w h e n the d o u b l e b o n d is c o n t a i n e d i n a n i n c i p i e n t a r o m a t i c system. D i s p r o p o r t i o n a t i o n a c t i v i t y i n the hydrogénation of c y c l o h e x e n e

(and

p r e s u m a b l y other i n c i p i e n t a r o m a t i c systems w i l l f o l l o w the same o r d e r ) decreases w i t h the m e t a l i n the o r d e r p a l l a d i u m > > p l a t i n u m > r h o d i u m (16).

A n e x a m p l e of the c o m p l i c a t i o n t h a t c a n be c a u s e d b y d i s p r o p o r -

t i o n a t i o n d u r i n g hydrogénation is f o u n d i n t h e a t t e m p t e d r e d u c t i o n of


11.

Double

RYLANDER

Bond

157

Isomerization

the d i e n o n e , V , to the saturated ketone over p a l l a d i u m - o n - c a r b o n i n ether. T h e p r o d u c t m i x t u r e consisted of a b o u t 2 0 % i n d a n e , 2 0 % 1-indanone,

and 4 5 %

4,5,6,7-tetrahydro-l-indanone

o x y g e n f u n c t i o n w o u l d be

expected

(14).

once the c o m p o u n d

cis-hexahydroL o s s of has

a r o m a t i c , for p a l l a d i u m makes t h e best k n o w n catalyst for

the

become selective

hydrogénation of a n a r o m a t i c ketone to a n a r o m a t i c a l c o h o l a n d

for

h y d r o g e n o l y s i s of the a r o m a t i c a l c o h o l to t h e a r o m a t i c h y d r o c a r b o n .


0

Ο

Ο

Loss of Optical

Activity

U n s a t u r a t e d o p t i c a l l y active c o m p o u n d s h a v i n g a n a s y m m e t r i c center accessible

to a m i g r a t i n g d o u b l e

hydrogénation (4).

bond may undergo

a c t i v e olefin ( — ) - 3 , 7 - d i m e t h y l - l - o c t e n e oxide, a catalyst of racemization, but

low

over

product was 4 3 - 5 2 %

(15).

R e d u c t i o n over p l a t i n u m

isomerization activity, resulted i n only v a r y i n g amounts

racemized.

of

3%

palladium-on-carbon,

the

R a c e m i z a t i o n , a n d therefore b y i n f e r -

ence i s o m e r i z a t i o n , w e r e decreased a n d b y bases.

racemization on

A n e x a m p l e is the hydrogénation of the o p t i c a l l y

b y pressure, b y catalyst i n h i b i t o r s ,

R e d u c t i o n at 1500 p s i g over p a l l a d i u m - o n - c a r b o n gave

o n l y 2 3 % r a c e m i z e d p r o d u c t , over a L i n d l a r catalyst (19)

at 1 a t m gave

1 6 % , a n d over p a l l a d i u m - o n - c a r b o n i n the presence of s m a l l q u a n t i t i e s of p o t a s s i u m h y d r o x i d e or p y r i d i n e gave 12 a n d 1 8 % r a c e m i z a t i o n , respectively.

C e r t a i n l y , i n this c o m p o u n d , m i g r a t i o n of the d o u b l e b o n d

afford t h e 2-octene w i l l result i n r a c e m i z a t i o n i f the olefin is before

saturation, but

other

pathways

to

to

desorbed

r a c e m i z a t i o n also m a y

be

operative. Stereochemistry T h e extent of d o u b l e b o n d m i g r a t i o n d u r i n g r e d u c t i o n of a n olefin m a y influence m a r k e d l y the stereochemistry of the r e s u l t i n g p r o d u c t .

A

s t r i k i n g e x a m p l e is p r o v i d e d b y the w o r k of S i e g e l a n d S m i t h ( 3 5 )

on

hydrogénation of 1,2-dimethylcyclohexene.

O v e r p l a t i n u m oxide i n acetic

a c i d , this olefin afforded 8 2 % cis- 1,2-dimethylcyclohexane, whereas

over

palladium-on-alumina

The

the p r o d u c t

contained

73%

trans-isomer.

e x p l a n a t i o n for this u n e x p e c t e d l y large percentage of trans-isomer lies i n d o u b l e b o n d m i g r a t i o n to the 2 - p o s i t i o n or to the m e t h y l e n e p o s i t i o n . T h e stereochemistry of the p r o d u c t is i n a sense t h e r e s u l t a n t of c o m p e t i -


158

PLATINUM

GROUP

METALS

AND

COMPOUNDS

t i o n b e t w e e n rates of hydrogénation a n d rates of i s o m e r i z a t i o n of the i n d i v i d u a l olefinic species. I n general, it seems easier to r a t i o n a l i z e a s t e r e o c h e m i c a l r e s u l t t h a n it is to p r e d i c t i t . T h e stereochemistry of hydrogénation of olefins is s u c h that h y d r o g e n u s u a l l y is a d d e d as i f b y cis a d d i t i o n f r o m the catalyst to the side of the m o l e c u l e that is a d s o r b e d o n it (34),

but unfortunately it

is not a l w a y s easy to d e c i d e w h i c h side of t h e m o l e c u l e w i l l a d s o r b o n the catalyst. T h e consequence of d o u b l e b o n d m i g r a t i o n o n the stereochemistry of the p r o d u c t is f r e q u e n t l y , therefore, not easy to p r e d i c t .

Hydrogénation of Aromatic Rings


A r o m a t i c c o m p o u n d s are r e d u c e d over the six p l a t i n u m m e t a l g r o u p catalysts at w i d e l y different rates, as expected, b u t a d d i t i o n a l l y t h e p r o d ucts of r e d u c t i o n f r e q u e n t l y v a r y w i t h the m e t a l used.

M a n y of these

results m a y be c o r r e l a t e d i n terms of t w o parameters not o b v i o u s l y c o n n e c t e d to a r o m a t i c p r o p e r t i e s : the r e l a t i v e tendencies of these catalysts to p r o m o t e

d o u b l e b o n d m i g r a t i o n i n olefins a n d to p r o m o t e

hydro-

genolysis of v i n y l i c a n d a l l y l i c functions.

Hydrogenolysis of Vinylic and Allylic Functions A g e n e r a l i z a t i o n d e r i v e d f r o m m a n y studies is that the toward

hydrogenolysis

of

vinylic

and

allylic

h a l o g e n increases i n the o r d e r r u t h e n i u m ^ platinum

Platinum Group Metals and Compounds;: A symposium sponsored by the Division of Inorganic Chemistry at the 158th meeting of the American Chemical Society (Advances in chemistry series 098)

Hydrocracking and Hydrotreating: A Symposium Sponsored by the Division of Petroleum Chemistry, Inc., at the 169th Meeting of the American Chemical Society, ... Penn., April (Acs Symposium Series, 20.)

Platinum Group Metals and Compounds

Air Pollution Effects on Plant Growth: A Symposium Sponsored by the Division of Agricultural and Food Chemistry at the 167th Meeting of the American (Acs Symposium Series, 3.)

Refining of Synthetic Crudes: Based on a symposium sponsored by the Division of Petroleum Chemistry at the 174th Meeting of the American Chemical Society (Advances in Chemistry Series 179)

Computer networking and chemistry: A symposium sponsored by the Division of Computers in chemistry at the 170th meeting of the American Chemical Society, ... Aug. 26-27, 1975 (ACS symposium series ; 19)

Inorganic Chemistry of the Main-Group Elements

Hydrocracking and Hydrotreating.. A Symposium Sponsored by the Division of Petroleum Chemistry

Van't Hoff - Le Bel centennial: A symposium sponsored by the Division of the History of Chemistry at the 168th meeting of the American Chemical Society, ... 11-12, 1974 (ACS symposium series ; no. 12)

Pesticide Chemistry in the 20th Century: A Symposium sponsored by the Division of Pesticide Chemistry at the 171st Meeting of the American Chemical Society, New York, April 6 - 8, 1976

Mechanism of pesticide action: A symposium sponsored by the Division of Pesticide Chemistry at the 167th meeting of the American Chemical Society, Los ... April 2-3, 1974 (ACS symposium series ; 2)

Arsenical pesticides: A symposium sponsored by the Division of Pesticide Chemistry at the 168th meeting of the American Chemical Society, Atlantic City, N.J., Sept. 9, 1974 (ACS symposium series ; 7)

The Chemistry of Heterocyclic Compounds, The Chemistry of 1,2,3-Thiadiazoles (Chemistry of Heterocyclic Compounds: A Series Of Monographs) (Volume 62)

The Chemistry of Organolithium Compounds

The Chemistry of Pincer Compounds

The chemistry of Organomagnesium Compounds

The chemistry of organomagnesium compounds

Structural Chemistry of Inorganic Actinide Compounds

Structural Chemistry of Inorganic Actinide Compounds

Structural Chemistry of Inorganic Actinide Compounds

The Chemistry of Organolithium Compounds

The Chemistry of Organozinc Compounds

Adsorption at interfaces : papers from a symposium honoring Robert D. Vold and Marjorie J. Vold sponsored by the Division of Colloid and Surface Chemistry at the 167th meeting of the American Chemical Society, Los Angeles, Calif., April 2-5, 1974

Chemistry of the Carbonyl Group

The Chemistry of Azido Group

The Colloid Chemistry of Silica (Advances in Chemistry Series)

Advances in Organic Chemistry, 50 (Advances in Inorganic Chemistry)

The Organometallic Chemistry of the Transition Metals

The organometallic chemistry of the transition metals

The Organometallic Chemistry of the Transition Metals

Chemical Nomenclature (Advances in Chemistry Series 008)

Platinum Group Metals and Compounds;: A symposium sponsored by the Division of Inorganic Chemistry at the 158th meeting of the American Chemical Society (Advances in chemistry series 098)

Hydrocracking and Hydrotreating: A Symposium Sponsored by the Division of Petroleum Chemistry, Inc., at the 169th Meeting of the American Chemical Society, ... Penn., April (Acs Symposium Series, 20.)