Platinum Group Metals and Compounds

3

Synthesis and Crystal Chemistry of Some

Downloaded by UNIV OF ARIZONA on December 11, 2012 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

N e w Complex Palladium Oxides OLAF MULLER and RUSTUM ROY Materials Research Laboratory, The Pennsylvania State University, University Park, Pa. 16802

The synthesis and crystal chemistry of six new complex pa ladium oxides are described. The blackPbPdO has been tentatively indexed on a hexagonal basis witha = 10.902A andc = 4.654A. Sr PdO is body-centered orthorhombic witha = 3.970A,b = 3.544A, and c = 12.84A; the structure proposed for this compound is closely related to the KNiF structure. Three new black compounds of the MePdO type have been synthesized. All three have the cubic NaPtO structure with unit cell constants a = 5.826A for SrPdO, a = 5.747A for CaPdO, anda = 5.742A for CdPd O . In the system Mg-Pd-O, a spinel phase is formed(a = 8.501A) whose stoichiometry is believed to be MgPdO. 2

0

0

2

0

2

3

0

0

4

3

4

x

3

4

0

3

4

0

3

3

4

0

4

0

2

4

Tn our recent work on the systems Rh-O, Pt-O (5,7), and Au-O (5,6) -*· at high oxygen pressures, we prepared new compounds in all three systems. We conducted a similar study in the system Pd-O, but were not able to synthesize any new binary oxides of palladium. The divalent oxide, PdO, appears to be stable even at high oxygen pressures. Our work on the platinum oxides was recently extended to some ternary systems, and we have already reported on the inverse spinels Mg Pt0 , Zn Pt0 (10), on Cd Pt0 with the Sr Pb0 structure (9), on the tetragonal Cui_ Pt O, and the orthorhombic CuPt 0 (8). Compounds of the type MePt O with Me = Cd, Zn, Mg, Ni were synthesized at 800°-900°C and oxygen pressures near 200 arm. These phases are described in greater detail by Hoekstra, Siegel, and Gallagher (2). We encountered some difficulty in preparing these compounds in a pure state. Apparently, the maximum temperatures attainable with our equip2

4

2

4

2

x

4

x

2

4

3

3

6

e

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

3.

M U L L E R

A N D

R O Y

New

Palladium

29

Oxides

m e n t ( . — 9 0 0 ° C ) are s t i l l too l o w for these reactions.

W e felt t h a t i t

m i g h t b e i n t e r e s t i n g to c o n d u c t a s i m i l a r s t u d y of some M e O - p a l l a d i u m o x i d e systems.

T h e present w o r k is c o n c e r n e d w i t h o u r s t u d y of

systems M e - P d - O , w h e r e M e =

the

P b , Sr, C a , C d , a n d M g .

R e l a t i v e l y l i t t l e is k n o w n a b o u t a n h y d r o u s oxides of p a l l a d i u m . T h e o n l y w e l l - c h a r a c t e r i z e d s i m p l e o x i d e is P d O , w h i c h has the P t S structure w i t h f o u r c o p l a n a r P d - O distances of 2.01 A (4,21).

Recently, G u i o t ( J )

p r e s e n t e d x - r a y e v i d e n c e s u g g e s t i n g t h a t a n e w p a l l a d i u m o x i d e surface c o m p o u n d is f o r m e d as a n i n t e r m e d i a t e step w h e n p a l l a d i u m m e t a l is o x i d i z e d i n a i r to P d O . H o w e v e r , the s t o i c h i o m e t r y of this c o m p o u n d Downloaded by UNIV OF ARIZONA on December 11, 2012 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

is u n k n o w n , since i t c a n be o b t a i n e d o n l y as a m i n o r constituent, w i t h m a j o r amounts of P d m e t a l a n d P d O . H i g h e r a n h y d r o u s oxides

(e.g.,

Pd0 )

firmly

2

h a v e b e e n r e p o r t e d , b u t t h e i r existence has n e v e r b e e n

established. R e l a t i v e l y f e w t e r n a r y p a l l a d i u m oxides h a v e b e e n r e p o r t e d i n the literature. V a r i o u s a l k a l i m e t a l - p a l l a d i u m oxides are k n o w n Intermediate compounds tems w i t h L n =

2

L a , N d , Sm, E u , G d , and D y (3).

p y r o c h l o r e s of the t y p e L n P d 0 2

delafossite-like c o m p o u n d s studied

(14,15,16).

h a v e b e e n f o u n d i n s e v e r a l L n 0 - P d O sys-

2

7

A t h i g h pressures,

c a n b e p r e p a r e d (19).

Recently, the

P d C o 0 , P d C r 0 , and P d R h 0 2

3

2

2

have

been

(18).

Experimental Techniques C o l d - s e a l stellite b o m b s a n d h i g h o x y g e n pressures w e r e u s e d as d e s c r i b e d p r e v i o u s l y (6, 7, 8, 9, 10). A n o r d i n a r y p o t f u r n a c e was u s e d for heat treatments c a r r i e d out i n air. A s s t a r t i n g m a t e r i a l s , p u r i f i e d p a l l a d i u m b l a c k ( F i s h e r Scientific C o . ) was m i x e d i n t i m a t e l y w i t h the other oxides o r h y d r o x i d e s [ P b O , S r ( O H ) · 8 H 0 , C a O , C d O , M g ( O H ) ] . T h e m i x t u r e s g e n e r a l l y w e r e i n s e r t e d i n t o g o l d foils a n d heat t r e a t e d u n d e r v a r i o u s c o n d i t i o n s of t e m p e r a t u r e a n d o x y g e n p r e s sure. T h e runs w e r e q u e n c h e d a n d the p r o d u c t s e x a m i n e d b y x - r a y diffraction. T h e x - r a y d i f f r a c t i o n patterns w e r e m a d e w i t h a P i c k e r diffractometer, u s i n g N i - f i l t e r e d C u K r a d i a t i o n a n d glass-slide m o u n t s . T o d e r i v e accurate u n i t c e l l constants, s l o w - s c a n x - r a y patterns w e r e i n t e r n a l l y s t a n d a r d i z e d w i t h N a C l , K C 1 , or S i . T h e i n t e g r a t e d intensities w e r e o b t a i n e d b y m e a s u r i n g the area u n d e r e a c h p e a k w i t h a p l a n i m e t e r . T h e c a t i o n analyses w e r e p e r f o r m e d b y c o n v e n t i o n a l w e t - c h e m i c a l t e c h n i q u e s . T h e o x y g e n content was d e t e r m i n e d b y a r e d u c t i o n m e t h o d a n d b y n e u t r o n a c t i v a t i o n analysis. 2

2

2

Results PbPd0 . 2

The black P b P d 0

2

is p r e p a r e d c o n v e n i e n t l y b y h e a t i n g a

1:1 P b O - P d b l a c k m i x t u r e i n a i r at a b o u t 6 0 0 ° - 7 0 0 ° C for s e v e r a l days.

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

P L A T I N U M

Table I.

M E T A L S

A N D

C O M P O U N D S

X - R a y Diffraction Powder D a t a for PbPdQj Hexagonal: a = 0

10.902A, c

0

— 4.654A

d obs. A

d cale, A

I obs.

hkl

4.72 3.544 2.833 2.727 2.607 2.360 2.327 2.282 2.087 1.964 1.784 1.769 1.693 1.657 1.593 1.573 1.531 1.492 1.438

4.72 3.539 2.832 2.726 2.607 2.360 2.327 2.282 2.087 1.964 1.784 1.770 1.693 1.657 1.593 1.574 1.531 1.492 1.438

2.0 5.1 100.0 19.7 2.8 17.0 12.0 1.7 4.1 4.0 18.4 20.3 1.5 15.1 22.8 1.8 1.3 0.4 16.6

200 111 211 220 301 400 002 311 202 321 420 222 331 402 511 600 103 113 521

1.392 1.375 1.363 1.334

1.391 1.375 1.363 1.335 (1.309 1.308 [1.304 1.261 1.239 1.2077 1.1987 (1.1802 U.1798 [1.1759 1.1635 1.1525 1.1446 1.1297 1.1196 1.0973

0.6 1.4 4.5 0.7

303 611 440 313 (620 441 [602 323 413 711 503 (800 333 [442 004 631 513 204 721 433

y


GROUP

1.305B 1.261 1.239 1.2075 1.1984 1.1779 1.1634 1.1523 1.1444 1.1296 1.1195 1.0972

1.0701 1.0527 1.0435 1.0358

{!S

1.0701 1.0526 1.0436 1.0356

1.0 0.6 1.2 0.2 0.6 12.4 2.8 8.0 9.5 1.4 0.4 0.7 9 8

3.7 10.7 3.1 6.8

{£

224 802 404 731


3.

M U L L E R

New

A N D R O Y

FaUadium

31

Oxides

A n analysis f o r o x y g e n b y n e u t r o n a c t i v a t i o n y i e l d e d 9 . 2 % lated: 9.26% Ο b y w e i g h t ) . P b P d 0

Ο

(calcu

is a p p a r e n t l y u n s t a b l e at t e m p e r a

2

tures a b o v e *—820 ° C , w h e r e a m i x t u r e of P b O a n d P b P d

is o b t a i n e d i n

3

p l a c e of P b P d 0 . 2

T h e x - r a y p o w d e r p a t t e r n of P b P d 0

2

( T a b l e I ) has b e e n t e n t a t i v e l y

i n d e x e d o n the basis of a h e x a g o n a l u n i t c e l l w i t h a = 0

4.654A.

T h i s m a y represent o n l y a p s e u d o c e l l .

10.902A a n d c

=

Q

N o single crystal data

are a v a i l a b l e , since the p r o d u c t c o u l d o n l y b e o b t a i n e d as a fine p o w d e r . T a b l e I i n d i c a t e s t h a t s e v e r a l extinctions o c c u r w h i c h are n o t c h a r a c t e r i s t i c f o r a n y h e x a g o n a l space g r o u p ; e.g., f o r KkO, h = Sr PdC>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

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

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

X - R a y Diffraction Powder D a t a for S r P d 0 2

O r t h o r h o m b i c : a — 3.970A, b 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

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.


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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.


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Platinum Group Metals and Compounds

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