Some Uranium-Transition Element Double Oxides - Advances in

16 Some Uranium-Transition Element Double Oxides Downloaded by UCSF LIB CKM RSCS MGMT on December 3, 2014 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch016

HENRY R. HOEKSTRA Chemistry Division, Argonne National Laboratory, Argonne, Ill. ROBERT H. MARSHALL Department of Chemistry and Physics, Memphis State University, Memphis, Tenn.

The preparation and properties of some double oxides of uranium with the seven transition elements from chromium through zinc are described. Thirteen compounds with the composition MUO or MU O were prepared by heating mixed oxides in air or in sealed silica tubes, by hydrothermal methods, and by high pressure techniques. Four of these compounds, (FeUO , FeU O , NiUO (20) and ZnUO ) have not been previously reported. NiUO has been pre pared in two crystal forms. The thermal stability, crystal structure, and infrared spectrum (from 1000—200 cm. ) of each of the 13 compounds has been investigated. The struc ture of FeUO and α-NiUO is similar to CrUO , while β-NiUΟ and ZnUO crystallize in the MgUO structure. FeU O has the pseudo-hexagonal lattice characteristic of the transition element triuranates. 4

4

3

10

3

10

4

4

4

-1

4

4

3

4

4

4

4

10

T V e c e n t investigations h a v e s h o w n that c h r o m i u m , manganese,

cobalt,

n i c k e l , c o p p e r , a n d z i n c oxides react w i t h u r a n i u m oxides at e l e v a t e d temperatures

to

form

double

oxides

M U 3 O 1 0 . T a b l e I lists eight c o m p o u n d s t h e r m a l s t a b i l i t y i n f o r m a t i o n has b e e n

with

the

formulas

MU0

4

and

for w h i c h some s t r u c t u r a l a n d reported.

T h e d o u b l e oxides are sometimes r e f e r r e d to as m o n o - a n d triuranates of the t r a n s i t i o n metals, even t h o u g h the existence of U ( V I ) i n some of the c o m p o u n d s

is q u e s t i o n a b l e .

T h i s is p a r t i c u l a r l y t r u e for

since d i v a l e n t c h r o m i u m is r e a d i l y o x i d i z e d .

W h e n the d o u b l e

CrU0

4

oxides

are r e f e r r e d to as uranates i n this p a p e r , it s h o u l d b e b o r n e i n m i n d that 211 In Lanthanide/Actinide Chemistry; Fields, P., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

212

LANTHANIDE/ACTINIDE

CHEMISTRY

the t e r m is u s e d for c o n v e n i e n c e a n d does not necessarily i n d i c a t e t h e existence of U ( V I ) i n these c o m p o u n d s . Table I. Compound

CrU0 MnU0 CoU0

Lattice

Downloaded by UCSF LIB CKM RSCS MGMT on December 3, 2014 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch016

4

4

4

MnU O CoU O NiU O CuU O ZnU ;O 3

1 0

8

1 0

3

:

a

1 0

3

Transition Metal Uranates

a

1 0

1 0

Parameters

a

b

c

4.868 6.645 6.497 3.79 3.79 3.78 3.77 7.56

5.048 6.983 6.952

11.785 6.749 6.497 4.14 4.08 4.04 4.17 16.418

— — — — —

Decomp. Τ

References

>1200°C. 1200°C. 1200°C. 1000°C. 940°C. 960°C. 910°C. 900°C.

3,8 2,4 2,4 5 5 5,9

5,10 15

D a t a o n M n , C o , N i , a n d C u triuranates refer to the a-UC>3 type pseudo-cell.

A m o n g the 1:1 oxides, C r U 0 and

is o r t h o r h o m b i c , space g r o u p C m m c ,

4

is b e l i e v e d to b e i s o s t r u c t u r a l w i t h B i V 0

CoU0

4

(7), while M n U 0

4

and

4

i n space g r o u p I m m a h a v e the | ( U 0 ) 0 2 | " c h a i n s c h a r a c t e r i s t i c 2

2

of the M g U 0

structure (22).

4

A

m o n o u r a n a t e of

copper, thermally

stable to 9 0 0 ° C . has also b e e n p r e p a r e d ( 5 ) , b u t its c e l l d i m e n s i o n s a n d s y m m e t r y are u n k n o w n . T h e c o m p l e x p s e u d o - h e x a g o n a l lattice of the 1:3 d o u b l e oxides appears to b e closely r e l a t e d to h e x a g o n a l « - U 0

3

(21).

S i n c e there is l i t t l e e v i d e n c e for s o l i d s o l u t i o n i n these c o m p o u n d s , the true u n i t c e l l of the t r i u r a n a t e s m u s t b e a m u l t i p l e of the s m a l l p s e u d o c e l l w h i c h contains o n l y 1/4 f o r m u l a w e i g h t . T h e l a r g e h e x a g o n a l c e l l r e p o r t e d for Z n U O i 3

0

w a s o b t a i n e d b y single c r y s t a l x - r a y m e t h o d s .

In

a d d i t i o n to the d r y p r e p a r a t i v e m e t h o d , a h y d r o t h e r m a l synthesis has b e e n r e p o r t e d for N i U O i 3

forms of C u U 0

4

0

and C u U O i

and Z n U 0

3

4

(18)

0

Synthesis of h e x a g o n a l

(9, 10).

has b e e n c l a i m e d , b u t b a s e d o n the

r e p o r t e d c e l l d i m e n s i o n s , the c o m p o u n d s

obtained were probably

the

c o r r e s p o n d i n g 1:3 d o u b l e oxides. A m o n g the t r a n s i t i o n metals f r o m c h r o m i u m t h r o u g h z i n c , i r o n r e m a i n s the o n l y e l e m e n t for w h i c h no d o u b l e o x i d e f o r m a t i o n w i t h u r a n i u m o x i d e has b e e n r e p o r t e d . B o t h the 1:1 a n d 1:3 c o m p o u n d s of m a n g a n e s e , c o b a l t , a n d c o p p e r h a v e b e e n p r e p a r e d , w h i l e o n l y the 1:1 c o m p o u n d of c h r o m i u m , a n d the 1:3 c o m p o u n d of n i c k e l a n d z i n c are k n o w n .

Experimental T h e s t a r t i n g m a t e r i a l s e m p l o y e d i n these syntheses w e r e reagent g r a d e c o m p o u n d s ; t h e y w e r e u s e d w i t h o u t f u r t h e r p u r i f i c a t i o n except for a p r e l i m i n a r y d e h y d r a t i o n of some of the oxides : U O , C r 0 , F e 0 , N i O , C u O , a n d Z n O w e r e d r i e d at 8 0 0 ° C ; U 0 at 5 0 0 ° C . T h e c o m p o 3

r

s

2

3

In Lanthanide/Actinide Chemistry; Fields, P., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

3

2

3

16.

H O E K S T R A

A N D

Uranium Double

M A R S H A L L

213

Oxides

s i t i o n of M n 0 a n d C o O was v e r i f i e d b y c h e m i c a l analysis a n d b y t h e r m o g r a v i m e t r i c analysis ( T G A ) .


2

2

a

P r e l i m i n a r y T G A a n d d i f f e r e n t i a l t h e r m a l analysis ( D T A ) curves w e r e o b t a i n e d o n i n d i v i d u a l oxides a n d o n the m i x e d t r a n s i t i o n m e t a l u r a n i u m oxides to ascertain the r e a c t i o n characteristics of the i n d i v i d u a l systems. T h e T G A d a t a w e r e o b t a i n e d o n a n A i n s w o r t h B R b a l a n c e e q u i p p e d w i t h a n A U recorder. Samples of 1 g r a m e a c h w e r e h e a t e d to 1 1 0 0 ° C . at 1 0 ° C . p e r m i n u t e . D T A i n f o r m a t i o n w a s o b t a i n e d o n a Tempres Research M o d e l D T - 4 A instrument. Samples w e i g h i n g a p p r o x i m a t e l y 50 m g . w e r e h e a t e d at 5 ° C . p e r m i n u t e to 1 2 5 0 ° C . D i f f e r e n t i a l temperatures w e r e m e a s u r e d w i t h a p l a t i n u m - p l a t i n u m 1 0 % r h o d i u m t h e r m o c o u p l e at a r e c o r d e r sensitivity of 20 m i c r o v o l t s p e r i n c h .

Synthetic

Procedures

D r y M e t h o d . T h o r o u g h l y g r o u n d m i x t u r e s of U 0 w i t h each of the t r a n s i t i o n e l e m e n t oxides w e r e h e a t e d i n a i r at a p p r o p r i a t e temperatures for u r a n a t e synthesis as i n d i c a t e d b y the D T A a n d T G A results. T h e h e a t i n g process was i n t e r r u p t e d several times to p e r m i t r e g r i n d i n g of the samples. Progress of the reactions was f o l l o w e d b y m e a s u r i n g w e i g h t c h a n g e , b y x - r a y d i f f r a c t i o n m e t h o d s , a n d b y i n f r a r e d analyses. P o w d e r patterns 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 N i filtered C u r a d i a t i o n . I n f r a r e d spectra w e r e o b t a i n e d o n K B r disks c o n t a i n i n g — 1 % of the d o u b l e oxide, or o n N u j o l m u l l s w h i c h w e r e s p r e a d o n K B r plates for the h i g h f r e q u e n c y p o r t i o n of the s p e c t r u m , a n 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 r e g i o n . T h e spectra w e r e r e c o r d e d o n a B e c k m a n I R - 1 2 spectrophotometer. 3

8

Synthesis of n i n e uranates discussed i n the i n t r o d u c t o r y m a t e r i a l w a s c o n f i r m e d i n the a i r - i g n i t e d samples of the m i x e d oxides. E a c h c o m p o u n d was i d e n t i f i e d b y its c h a r a c t e r i s t i c x - r a y d i f f r a c t i o n p a t t e r n . S o m e e v i d e n c e was f o u n d for a n a d d i t i o n a l d o u b l e o x i d e i n the c o p p e r u r a n i u m o x i d e system. T h e r m a l d e c o m p o s i t i o n of C u U 0 or C u U O i i n the t e m p e r a t u r e i n t e r v a l b e t w e e n 900° a n d 1000°C. appears to g i v e a r h o m b o h e d r a l structure r e s e m b l i n g t h a t of N a U 0 . M e a s u r e m e n t o f o x y g e n loss suggests a f o r m u l a of C u 0 0 for the n e w c o m p o u n d , b u t its r e s t r i c t e d s t a b i l i t y range has p r e v e n t e d i s o l a t i o n of a p u r e phase to c o n f i r m the p o s t u l a t e d f o r m u l a . N o e v i d e n c e was o b t a i n e d i n these experiments for the f o r m a t i o n of a n y d o u b l e o x i d e i n the i r o n - u r a n i u m o x i d e system n o r for the existence of C r U O i , N i U 0 , or Z n U 0 . 4

2

2

2

2

3

0

7

7

3

0

4

4

C r U 0 , M n U 0 , and C o U 0 can be synthesized conveniently b y h e a t i n g the m i x e d oxides for a d a y at 1 0 0 0 ° - 1 1 0 0 ° C . T h e c o r r e s p o n d i n g c o p p e r c o m p o u n d s h o u l d n o t b e h e a t e d a b o v e 8 7 5 ° C . since o x y g e n loss b e c o m e s a p p r e c i a b l e a b o v e this t e m p e r a t u r e . T h e o x y g e n content of m o n o u r a n a t e samples p r e p a r e d at the temperatures i n d i c a t e d is w i t h i n 1 % of the t h e o r e t i c a l v a l u e . T h e manganese a n d c o b a l t c o m p o u n d s c a n n o t b e p r e p a r e d b e l o w 1 0 0 0 ° C . since the 1:3 c o m p o u n d w i l l b e f o r m e d r a t h e r t h a n the d e s i r e d 1:1 oxide. I n some instances a n n e a l i n g of M n U 0 or C0UO4 at ^ - 8 0 0 C . has l e d to d i s p r o p o r t i o n a t i o n to the 1:3 d o u b l e oxide a n d M n 0 or C o 0 . 4

4

4

o

4

2

3

3

4


214

LANTHANIDE/ACTINIDE

CHEMISTRY

T h e five triuranates c a n be p r e p a r e d at 8 7 5 ° C . N i c k e l , c o p p e r , a n d z i n c triuranates are r e a d i l y o b t a i n e d as s t o i c h i o m e t r i c c o m p o u n d s ( ± 0 . 0 5 a t o m o x y g e n ) , b u t the c o r r e s p o n d i n g manganese a n d c o b a l t c o m p o u n d s t e n d to r e m a i n o x y g e n deficient. A f t e r three days at 9 0 0 ° C . the c o m p o sitions c a l c u l a t e d for t y p i c a l p r e p a r a t i o n s w e r e M n U a 0 57 a n d C o U 0 . 4 . O x y g e n was a b s o r b e d s l o w l y w i t h c o n t i n u e d h e a t i n g a n d r e m a i n e d m o r e t h a n 1 % l o w e v e n after three months at 9 0 0 ° C .


9

3

9

6

Sealed T u b e Method. N o e v i d e n c e for c o m p o u n d f o r m a t i o n w a s o b s e r v e d w h e n m i x t u r e s of i r o n a n d u r a n i u m oxides w e r e h e a t e d i n a i r to temperatures as h i g h as 1 2 0 0 ° C . S u b s t i t u t i n g f e r r i c a n d u r a n y l nitrates for the oxides as s t a r t i n g m a t e r i a l s also p r o v e d unsuccessful. F e r r i c o x i d e a n d U O o 4 w e r e the o n l y p r o d u c t phases, thus g i v i n g a n e m p i r i c a l f o r m u l a of F e U 0 . i 4 i n the 1:1 m i x t u r e , a n d F e U 0 i n the 1:3 m i x t u r e . U n l i k e the s i t u a t i o n e n c o u n t e r e d i n the other d o u b l e o x i d e systems, the i r o n uranates do not a p p e a r to h a v e sufficient t h e r m o d y n a m i c s t a b i l i t y to b e s y n t h e s i z e d at a m b i e n t o x y g e n pressure. T o a c h i e v e the r e q u i r e d o x y g e n c o m p o s i t i o n , the c a l c u l a t e d a m o u n t s of i r o n a n d u r a n i u m oxides ( E q u a t i o n 1, 2 ) 6

3

4

9

4 2

1050°C. FeO + U 0

_>

3

FeU0

(la)

4

or 1050°C. 2Fe 0 2

Fe 0 2

+ U O

3

3

+ U O

3

3

s

s

+ U0

2

->

4FeU0

+ 3U0

3

880°C. _>

2FeU O 3

(lb)

4

(2)

1 0

w e r e sealed i n t o e v a c u a t e d s i l i c a tubes a n d h e a t e d at the i n d i c a t e d t e m peratures for t w o weeks. U n d e r these c o n d i t i o n s r e a c t i o n d i d o c c u r to g i v e the d e s i r e d p r o d u c t s . C o m p l e t e r e a c t i o n w a s difficult to a c h i e v e , p a r t i c u l a r l y w i t h the 1:3 m i x t u r e . T r a c e s of r e s i d u a l U 0 w e r e i d e n t i fiable i n the x - r a y films of e v e r y p r o d u c t . O x y g e n analysis of F e U O i o was o b t a i n e d b y h e a t i n g the s a m p l e at 1000°C. f o r 8 hrs. to d e c o m p o s e the d o u b l e oxide, t h e n at 7 5 0 ° C . for several hours to g i v e F e O a n d U 0 as final p r o d u c t s . T h e o b s e r v e d w e i g h t loss c o r r e s p o n d e d to a f o r m u l a of F e U O . i for the starting m a t e r i a l . 3

8

3

2

3

t 3

8

3

1 0

±

0

Hydrothermal Method. T h e h y d r o t h e r m a l experiments w e r e c a r r i e d out i n a 20 cc. p l a t i n u m - l i n e d M o r e y b o m b ( 1 7 ) . T h e e x p e r i m e n t a l c o n d i t i o n s w e r e a p p r o x i m a t e l y those u s e d b y G i l l a n d M a r s h a l l ( 8 ) to s y n thesize C u U O i . T h e t r a n s i t i o n element oxide ( C r 0 , M n 0 , F e O , C o O , N i O , C u O , or Z n O ) a n d y - U 0 w e r e p l a c e d i n the b o m b w i t h 10 m l . 0 . 0 6 M H S 0 . T h e m i x e d oxide samples w e i g h e d a p p r o x i m a t e l y 2.5 grams i n a 1 M : 4 U m o l a r r a t i o . T h e excess u r a n i u m was a d d e d to attain c o m p l e t e r e a c t i o n of the t r a n s i t i o n element oxide. T h e sealed vessel was h e a t e d 5 days or l o n g e r at 3 5 0 ° C . T h e r e s u l t i n g s o l i d p r o d u c t was t h e n p u r i f i e d w i t h several treatments of 0 . 0 6 M H S 0 . Excess u r a n i u m present as H U 0 w a s d i s s o l v e d b y this p r o c e d u r e to l e a v e the p u r e t r i u r a n a t e for x - r a y a n d i n f r a r e d analysis. 3

0

2

3

3

3

2

4

2

2

2

4

7


4

16.

H O E K S T R A

A N D

Uranium

M A R S H A L L

Double

Oxides

215

T h e s e experiments i n d i c a t e that the h y d r o t h e r m a l m e t h o d c a n b e u s e d to p r e p a r e manganese, c o b a l t , a n d z i n c triuranates as w e l l as the n i c k e l a n d c o p p e r c o m p o u n d s . N o e v i d e n c e w a s o b t a i n e d for a r e a c t i o n b e t w e e n either C r 0 or F e 0 a n d U 0 u n d e r the e x p e r i m e n t a l c o n d i tions used. W h e n F e O was h e a t e d w i t h U 0 , the p r i n c i p a l r e a c t i o n o b s e r v e d was a n o x i d a t i o n of F e O to F e 0 b y h e x a v a l e n t u r a n i u m . H y d r o t h e r m a l experiments w i t h 1:1 m i x t u r e s of the t r a n s i t i o n elem e n t o x i d e a n d u r a n i u m t r i o x i d e w i t h a single e x c e p t i o n , d i d not g i v e the d e s i r e d M U 0 c o m p o u n d s . T h e C u O - U 0 e x p e r i m e n t gave a m i x ture of C u U 0 , C u U O i o , a n d a basic c o p p e r sulfate. A l l attempts to p r e p a r e 1:1 d o u b l e oxides of the four r e m a i n i n g m e m b e r s of the series l e d to the f o r m a t i o n of the c o r r e s p o n d i n g t r i u r a n a t e phase m i x e d w i t h u n r e a c t e d t r a n s i t i o n element oxide. H i g h Pressure Method. Sometimes, c e r t a i n s o l i d phases or c o m p o u n d s w h i c h d e f y synthesis at a m b i e n t pressure c a n b e p r e p a r e d at h i g h pressures. C o n d i t i o n s are p a r t i c u l a r l y f a v o r a b l e i f the p r o d u c t m o l a r v o l u m e is a p p r e c i a b l y less t h a n that of the reactants. S i n c e the other t e c h n i q u e s f a i l e d to p r o d u c e either N i U 0 or Z n U 0 , the p r e p a r a t i o n of these c o m p o u n d s was a t t e m p t e d b y a h i g h pressure m e t h o d . T h e h i g h pressure e q u i p m e n t u s e d i n these experiments was a 2,000-8,000 t o n t e t r a h e d r a l a n v i l a p p a r a t u s o b t a i n e d f r o m B a r o g e n i c s , I n c . T h e s a m p l e assembly a n d the p r o c e d u r e u s e d h a v e b e e n d e s c r i b e d elsewhere (13) a n d w i l l not b e r e p e a t e d i n d e t a i l here. B r i e f l y , 1:1 m i x tures of N i O -f- U 0 a n d Z n O - f U 0 w e i g h i n g a p p r o x i m a t e l y 1 g r a m e a c h w e r e w r a p p e d i n p l a t i n u m f o i l envelopes, a n d i n s e r t e d i n t o the s a m p l e c a v i t y 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 ( F i g u r e 1 ). T h e oxides w e r e t h e n h e a t e d for 30 m i n u t e s at 1 0 0 0 ° C . w h i l e exposed to a pressure of 40 k b a r . A f t e r b e i n g r e t u r n e d to a m b i e n t c o n d i t i o n s , the samples w e r e i n v e s t i g a t e d b y x - r a y a n d i n f r a r e d t e c h n i q u e s . T h e synthesis of N i U 0 a n d Z n U 0 w a s c o n f i r m e d i n e v e r y instance. 2

3

2

3

8

3

2

3

4

3


4

3

4

3

4

3

4

4

Figure

1.

High

pressure

sample

assembly


216

LANTHANIDE/ACTINIDE CHEMISTRY

A n a t t e m p t to p r e p a r e F e U 0 at 1 0 0 0 ° C . a n d 30 k b a r . p r o v e d u n successful, b u t C0UO4 a n d M n U 0 w e r e s y n t h e s i z e d u n d e r s i m i l a r c o n d i t i o n s . A t t e m p t s to p r e p a r e 1:3 d o u b l e oxides w e r e u n s u c c e s s f u l , p r e s u m a b l y because these c o m p o u n d s d o not possess a c l o s e - p a c k e d structure (See d i s c u s s i o n of M U 3 O 1 0 s t r u c t u r e ) . 4

4

Results and Discussion C r y s t a l S t r u c t u r e . W i t h the synthesis of F e U 0 , N i U 0 4


the 1:1 d o u b l e o x i d e series is c o m p l e t e T h r e e s t r u c t u r e types

are f o r m e d

C r U 0 , F e U 0 , and « N i U 0 , (b) 4

and

4

(c)

4

and Z n U 0 ,

4

4

from chromium through zinc.

among

the seven

compounds:

(a)

M n U 0 , C o U 0 , /2-NiU0 , Z n U 0 , 4

4

4

4

CuU0 . 4

O u r x-ray powder data on C u U 0

4

are i n a c c o r d w i t h the "d" values

p u b l i s h e d b y B r i s i ( 5 ) ; the s y m m e t r y appears to be m o n o c l i n i c , b u t the space g r o u p a n d u n i t c e l l parameters h a v e not b e e n r e s o l v e d . d i m e n s i o n s c a l c u l a t e d f r o m o u r p r e p a r a t i o n s of C r U 0 , CoU0

The cell

MnU0 ,

4

4

and

are i n excellent agreement w i t h those g i v e n i n T a b l e I a n d n e e d

4

not b e r e p e a t e d here. the t w o N i U 0

4

P o w d e r diffraction data on F e U 0 , Z n U 0 , and 4

4

phases are g i v e n i n T a b l e I I . T h e c e l l parameters c a l c u

l a t e d f r o m these d a t a a r e : FeU0 a-NiU0 0-NiUO ZnU0 4

4 4

4

a = 4.883 4.820 6.472 6.492

± 0.009 ± 0.006 ± 0.012 ± 0.012

b = 5.099 5.188 6.870 6.994

± ± ± ±

0.009 0.006 0.012 0.012

c = 11.879 11.627 6.472 6.574

± ± ± ±

0.022A. 0.012A. 0.012A. 0.012A.

It s h o u l d b e n o t e d that c/a = 1 i n the p s e u d o - t e t r a g o n a l u n i t c e l l of C o U 0 a n d β - Ν ί ϋ 0 , w h i l e the larger M n a n d Z n ions f o r m m o n o u r a nates w i t h c/a > 1. 4

4

B o t h forms of N i U 0 h a v e b e e n s y n t h e s i z e d u n d e r s i m i l a r c o n d i tions, a n d one h i g h pressure p r e p a r a t i o n consisted of a m i x t u r e of the t w o phases. N o t e n d e n c y c o u l d be d i s c e r n e d for c o n v e r t i n g a to β, or the reverse, d u r i n g a n n e a l i n g experiments. A t present no means is k n o w n to d e t e r m i n e w h i c h phase w i l l be o b t a i n e d i n a n y single e x p e r i m e n t . T h e m o l a r v o l u m e s at a t m o s p h e r e pressure are s i m i l a r b u t suggest that the β - f o r m s h o u l d be p r e f e r r e d as the pressure is i n c r e a s e d . I n S e p t e m b e r 1966, Y o u n g r e p o r t e d the synthesis of the β phase of N i U 0 at h i g h pressure ( 2 0 ) . 4

4

T h e lattice parameters of the five triuranates p r e p a r e d i n the d r y w a y are i n excellent agreement ( ± 0 . 0 1 A . ) w i t h the d a t a g i v e n i n T a b l e I. dry

A c o m p a r i s o n of p o w d e r patterns o b t a i n e d f r o m h y d r o t h e r m a l a n d p r e p a r a t i o n s indicates that o n l y M n U ^ O i o shows

any

appreciable

d e p e n d e n c e u p o n the p r e p a r a t i v e m e t h o d e m p l o y e d .

The

pseudo-cell

d i m e n s i o n s are a = used, a = followed.

3.80A. a n d c =

3.73A. a n d c =

4.14A. w h e n the d r y synthesis is

4.12A. w h e n the h y d r o t h e r m a l p r o c e d u r e is

A n a l y t i c a l results h a v e c o n f i r m e d the

manganese-to-uranium


16.

H O E K S T R A

A N D

Uranium Double

M A R S H A L L

r a t i o i n the h y d r o t h e r m a l c o m p o u n d

217

Oxides

(1.02 M n : 3.00 U ) .

A n identical

r a t i o w a s f o u n d for the d r y m e t h o d d o u b l e oxide. It is a p p a r e n t f r o m the p o w d e r d i f f r a c t i o n d a t a o n F e U a O i o g i v e n i n T a b l e I I that the i r o n c o m p o u n d

closely resembles the other

five

m e m b e r s of the t r i u r a n a t e series. D i m e n s i o n s of the h e x a g o n a l p s e u d o c e l l o b t a i n e d f r o m these d a t a are a — 3.76A. a n d c =

4.03A. T r a c e s of

U3O8 persist i n the t r i u r a n a t e p r e p a r a t i o n s e v e n after the reactants h a v e Downloaded by UCSF LIB CKM RSCS MGMT on December 3, 2014 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch016

b e e n h e a t e d for s e v e r a l weeks at 9 0 0 ° C . caused b y residual U 0 3

8

D i f f r a c t i o n patterns free of lines

w e r e o b t a i n e d b y u s i n g a s l i g h t excess of i r o n

o x i d e i n the r e a c t a n t m i x t u r e . N o shift i n F e U s O i o l i n e positions w a s n o t e d i n these experiments. S i n c e x - r a y d i f f r a c t i o n d a t a on the t r i u r a n a t e p o w d e r s d i d not a p p e a r to afford p r o m i s e for d e t e r m i n i n g the t r u e c r y s t a l s t r u c t u r e of these c o m p o u n d s , efforts w e r e m a d e to p r e p a r e m a t e r i a l s s u i t a b l e for single c r y s t a l studies. S e v e r a l crystals of the d e s i r e d size w e r e o b t a i n e d i n one h y d r o t h e r m a l N1U3O10

preparation.

I n a d d i t i o n , crystals of

CuU Oi 3

and

0

Z n U a O i o w e r e p r e p a r e d b y the r e a c t i o n of U O 3 w i t h the m o l t e n a n h y d r o u s t r a n s i t i o n element c h l o r i d e i n e v a c u a t e d a n d sealed s i l i c a tubes at 6 0 0 ° 6 5 0 ° C . for s e v e r a l weeks. T h e s e crystals of the triuranates w e r e i n v a r i a b l y t w i n n e d a b o u t the V

axis. T h i s t w i n n i n g gives a n a p p a r e n t h e x a g o n a l

s y m m e t r y to the c r y s t a l , a l t h o u g h the true s y m m e t r y is l o w e r .

Several

crystals w h i c h c o n t a i n e d r e l a t i v e l y large u n t w i n n e d segments w e r e c u t so as to isolate the u n t w i n n e d p o r t i o n .

P r e l i m i n a r y single c r y s t a l d a t a

o b t a i n e d o n these pieces gave the f o l l o w i n g c e l l parameters for N i U O i o : 3

a — 7.525A, b = a =

6.545A., c =

16.126A., β ^

9 1 ° C . a n d for C u U O i : 8

0

7.575A., b — 6.473A., c — 16.679A., β g* 9 1 ° C . T h e MU3O10 S t r u c t u r e . I p p o l i t o v a , et al. (15)

c r y s t a l a n d p o w d e r x - r a y w o r k that the Z n U O i 3

0

c o n c l u d e d f r o m single

c r y s t a l l a t t i c e is h e x a g o

n a l a n d that its p s e u d o - c e l l d i m e n s i o n s i n d i c a t e a close s t r u c t u r a l s i m i l a r i t y to a - U 0 . Z a c h a r i a s e n (11 ) s h o w e d t h a t the a phase c a n b e w r i t t e n 3

as U O ( 0 )

2

since t w o types of o x y g e n sites o c c u r i n the c r y s t a l . T w o of

e v e r y three o x y g e n atoms are l o c a t e d i n U ( 0 )

2

layers a l o n g the

' V

d i r e c t i o n . T h e layers are j o i n e d b y the r e m a i n i n g o x y g e n a t o m to f o r m U—O—U—Ο chains i n the "c"

d i r e c t i o n . E a c h u r a n i u m is b o n d e d to six

o x y g e n atoms i n the l a y e r a n d to t w o o x y g e n atoms i n the c h a i n . C o n v e r s i o n of a - U 0

3

to M U O i 3

i n v o l v e s the r e p l a c e m e n t of

0

f o u r t h of the u r a n i u m atoms b y d i v a l e n t m e t a l ions. o x y g e n - m e t a l r a t i o is decreased

one-

A s a r e s u l t the

to 2.5:1, a n d o x y g e n " v a c a n c i e s "

are

c r e a t e d i n the chains or i n the sheets. I p p o l i t o v a et al. r e p o r t e d that the "a" d i m e n s i o n of the t r u e t r i u r a n a t e c e l l is t w i c e that of a - U 0 , o w i n g 3

to the o r d e r e d d i s t r i b u t i o n of u r a n i u m a n d z i n c atoms i n the l a t t i c e , a n d t h a t the t r u e "c"

d i m e n s i o n of Z n U O 3

i 0

is f o u r times that of


a-U0

3

218

LANTHANIDE/ACTINIDE

Table II.

Powder Diffraction Element-Uranium

FeOO

a-muo


k

ί

d

F W M MW F F VVW F VVW F F F F VW W F F MW F VVW F VVW F W F F F VVW F VVW F F

5.900 3.863 3.366 3.070 2.975 2.629 2.571 2.546 2.433 2.346 2.254 2.218 2.143 2.064 1.9620 1.9323 1.8870 1.7686 1.6892 1.6365 1.6082 1.5902 1.5678 1.5348 1.5187 1.5048 1.4897 1.4774 1.4299 1.3590 1.3441 1.3321

CHEMISTRY

u

hkl 002 012 111 103 004 113 014 020 200 022 202 121 105 212 123 024 204 214, 220 222 125, 032 301 131 026 206, 3 1 1 , 1 1 7 224 303 133, 008 034 018 232,127 305 135

F = faint, W = weak, M = m e d i u m , S =

I

d

VVW F W S M F W W VW F B-F VW W M VW F F M M F F VVW W F W B-W M F F VW F F

5.773 4.426 3.865 3.367 3.006 2.905 2.586 2.533 2.402 2.365 2.233 2.094 2.034 1.9627 1.9369 1.8515 1.8034 1.7612 1.7424 1.6859 1.6564 1.6281 1.6085 1.5505 1.5182 1.5004 1.4810 1.4509 1.3987 1.3637 1.3424 1.3333

hkl 002 101 012 111 103 004 020 014 200 022 121, 202 105 212 123 024,115 204 016 220 214 222 032 125 131 026 311 117,133 303 008, 216 018 232 127 135

strong, B = b r o a d .

b e c a u s e the layers are s u p e r p o s e d so that the first l a y e r is n o t r e p e a t e d u n t i l the fifth l a y e r — i . e . , Zn 1

U-O-U-O-U 2 3 4

Zn 5

U-O-U 6 7

E a c h m e t a l a t o m is b o n d e d to six o x y g e n atoms w i t h i n its l a y e r , e a c h u r a n i u m is b o n d e d to a t o t a l of seven or e i g h t o x y g e n atoms, a n d e a c h z i n c to six o x y g e n atoms. T h i s structure is d e r i v e d f r o m the a - U 0 b y r e m o v i n g o x y g e n atoms f r o m the chains.


3

lattice

16.

H O E K S T R A

A N D M A R S H A L L

Uranium

Double

Oxides

219

D a t a on Transition Oxides β-NiUOt


d

FeU O

ZnUO,

3

f

hkl

ί

d

F VW VVW M M F VW VW VW VW VVW F M F VVW VVW VVW F VVW

4.679 4.548 3.411 3.218 2.736 2.665 2.351 2.282 2.054 2.045 1.9013 1.7926 1.7556 1.7354 1.7159 1.6157 1.6092 1.5680 1.5303

011 101 020 200, 002 121 211, 112 022, 220 202 013 103, 301 222 231,132 321, 123 312, 213 040 400, 004 141 033 411, 114

W F M M M F W W W VVW VVW F M M VW W w VW w

4.568 3.473 3.272 3.226 2.780 2.683 2.374 2.301 2.067 2.051 1.9217 1.8139 1.7825 1.7697 1.7476 1.6394 1.6195 1.5814 1.5383

VW F VVW F VVW VVW F F F VW F VVW F

1.5144 1.4618 1.4456 1.4115 1.3929 1.3714 1.3323 1.3153 1.2943 1.2720 1.2409 1.1905 1.1844

240, 042 420 204,402 332, 233 323 242 422, 224 341, 143 431, 134 413, 314, 015 152, 251 521, 125 215, 512

F VVW VVW VW VVW F F F F F VVW VVW VVW

1.4839 1.4639 1.4547 1.4079 1.3940 1.3508 1.3365 1.3045 1.2839 1.2765 1.2075 1.1968 1.1894

I

hkl 101 020 200 002 121 112 022 202 301, 013 103 222 132 321 123 040 400 004 033 303, 240 042,114 420 402 204 323 242 422 341 134 413, 314 015 521 440,125 044,215

10

d

VVW VVW VVW MS F VW

5.005 4.639 4.100 4.009 3.625 3.414

MS F

3.238 2.922

M M VW VVW VW VW F VVW

2.544 2.514 2.014 1.9478 1.8831 1.8686 1.7904 1.7648

W W F F VVW VVW VVW F F F F B-F B-F

1.7193 1.7045 1.6436 1.6245 1.5821 1.5533 1.5175 1.4202 1.3809 1.3457 1.3206 1.2768 1.2407

O u r p r e l i m i n a r y single c r y s t a l d a t a o n the c o r r e s p o n d i n g c o p p e r d o u b l e o x i d e i n d i c a t e that the C u U O i 3

0

l a t t i c e contains o x y g e n v a c a n c i e s

i n t h e sheets, r a t h e r t h a n the chains. F i g u r e 2 d e p i c t s the a t o m i c a r r a n g e m e n t w i t h i n e a c h l a y e r of the c r y s t a l . T h e r e c t a n g u l a r base of the true u n i t c e l l , a n d the n e a r - h e x a g o n a l p s e u d o - c e l l are o u t l i n e d .

One-fourth

of the o x y g e n atoms w i t h i n e a c h l a y e r are m i s s i n g . T h e r e m a i n i n g o x y gens are a r r a n g e d so that e v e r y c o p p e r a t o m is b o n d e d to f o u r oxygens i n a square-planar configuration.

I n a d d i t i o n , t w o w e a k e r b o n d s are

f o r m e d w i t h oxygens s i t u a t e d a b o v e a n d b e l o w the p l a n e . T w o different


220

LANTHANIDE /ACTINIDE

CHEMISTRY

u r a n i u m sites c a n b e d i s t i n g u i s h e d ; one is b o n d e d to f o u r " l a y e r " oxygens, the o t h e r to five. I n e a c h instance t w o of t h e U—Ο b o n d s ( i n d i c a t e d b y d o u b l e lines i n F i g u r e 2) are shorter t h a n the r e m a i n i n g bonds.

These

p a i r e d , v i r t u a l l y l i n e a r , short bonds c a n be c o n s i d e r e d to f o r m u r a n y l groups i n the C u U 3 O

1 0

l a t t i c e . T h e u r a n y l b o n d lengths are a p p r o x i

m a t e l y 1.8A., w h i l e the l o n g e r U - O b o n d s i n the sheets r a n g e f r o m 2.25 to 2.45A. T h e c h a i n U - O b o n d lengths ( 2 . 0 8 A . ) are v i r t u a l l y i d e n t i c a l w i t h the c o r r e s p o n d i n g b o n d s i n « - U 0 . Downloaded by UCSF LIB CKM RSCS MGMT on December 3, 2014 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch016

3

Figure 2.

CuU O 3

10

Structure

A l t h o u g h our results i n d i c a t e that the C U U O I U o x y g e n " v a c a n c i e s " 3

o c c u r i n the layers r a t h e r t h a n a l o n g the chains, i t cannot b e a s s u m e d that a s i m i l a r configuration occurs i n the r e m a i n i n g triuranates. B a s e d o n the t r a n s i t i o n element i o n i c r a d i i g i v e n b y A h r e n s ( I ), one notes that the V

d i m e n s i o n of the n i c k e l , cobalt, z i n c , a n d manganese

double

oxides u n i t cells f o l l o w i n the same o r d e r as the respective t r a n s i t i o n element i o n i c r a d i i , b u t that the C u U g O i o " c " d i m e n s i o n is a b n o r m a l l y long.

T h i s fact suggests t h a t d i r e c t i o n a l covalent b o n d i n g governs the

a t o m i c a r r a n g e m e n t i n this c o m p o u n d since c o v a l e n t l y b o n d e d c o p p e r ( I I ) f r e q u e n t l y forms f o u r s t r o n g b o n d s i n a p l a n e w i t h t w o w e a k b o n d s at r i g h t angles to the p l a n e .


16.

H O E K S T R A

A N D

Uranium

M A R S H A L L

Double

221

Oxides

Thermal Stability. D T A a n d T G A studies h a v e b e e n m a d e o n t h e 13 d o u b l e oxides s y n t h e s i z e d i n this i n v e s t i g a t i o n . T h e d e c o m p o s i t i o n temperatures l i s t e d i n T a b l e I I I are those t e m p e r a t u r e s at w h i c h t h e D T A trace first s h o w e d a d e v i a t i o n f r o m its base l i n e . S u p p l e m e n t a r y experiments h a v e s h o w n t h a t t h e r m a l d e c o m p o s i t i o n at constant t e m p e r a t u r e occurs 2 0 - 3 0 ° C . b e l o w the D T A t e m p e r a t u r e s g i v e n i n T a b l e


III. Table III. Thermal Decomposition of Transition Element-Uranium Double Oxides Compound CrU0

Dec. T,°C. >1250°C.

4

840°C. 1190°C.

4

920°C. 900°C.

Products N o decomposition C u b i c phase 4Mn 0 U0 + Fe 0 C u b i c phase + CoO NiU O + NiO CuU 0 (?)

925°C.

U0

4

MnU0

1110°C.

4

3

FeU0 CoU0

4

NiU0 CuU0

4

2

1 0

2

Dec. T,°C. Products 900 M n U O ( I I )

MnU O (II)

1015

3

1 0

3

1 0

3

1 0

MnU0

7

3

FeU O CoU O 3

1 0

3

1 0

4

2

6

+ U0 , 2

NiU O CuU O 3

1 0

3

1 0

910 965

Fe 0 + U 0 CoU0 + U 0

980 900

Ni0 + U 0 Cu U 0 (?) + uo ZnO + U 0

2

3

2

4

2

2

2

ZnU0

4

4

2 6

3

Compound MnU O (I)

+ ZnO

930

ZnU O a

2

6

2

6

6 2 e

7

6

A l l d e c o m p o s i t i o n reactions are e n d o t h e r m a l except t h a t of F e U 0 , 4

p r e s u m a b l y because this is the o n l y r e a c t i o n w h i c h i n v o l v e s o x i d a t i o n of the d o u b l e oxide.

N o significant difference w a s n o t e d i n t h e D T A or

T G A curves of the t w o N i U 0

4

phases. I t is i n t e r e s t i n g to note the alter-

n a t i n g p a t t e r n i n the d e c o m p o s i t i o n reactions of the uranates. T h e i r o n , n i c k e l , a n d z i n c d o u b l e oxides t e n d to d e c o m p o s e d i r e c t l y i n t o t h e i r constituent oxides, w h i l e the manganese, c o b a l t , a n d c o p p e r

compounds

d e c o m p o s e to other d o u b l e oxides. T h e p a t t e r n is not c a r r i e d o v e r i n t o the d e c o m p o s i t i o n t e m p e r a t u r e s . I n this instance, the t h e r m a l s t a b i l i t y of the d o u b l e oxides appears to v a r y d i r e c t l y w i t h the c h a r a c t e r i s t i c t r a n s i t i o n e l e m e n t o x i d a t i o n states: C r ( I I I ) > M n , C o ( I I I , I I ) > N i , Z n ( I I ) >

C u ( I I , I ). T h e i r o n c o m p o u n d s constitute a definite e x c e p t i o n to this

pattern. T h e t w o forms of M n U s O i o s h o w differences i n t h e i r d e c o m p o s i t i o n b e h a v i o r as w e l l as i n their c e l l d i m e n s i o n s . T h e h y d r o t h e r m a l t r i u r a n a t e ^ ) loses — 0 . 6 a t o m of o x y g e n at 9 0 0 ° C . as it is c o n v e r t e d to t h e d r y m e t h o d oxide ( I I ) . T h e final t w o d e c o m p o s i t i o n steps ( 1 ) to M n U 0 +

U0

forms.

2

6

4

a n d ( 2 ) to a c u b i c phase ^ ~ M n U 0 . r > , are i d e n t i c a l i n the t w o 3

8

It was n o t e d earlier t h a t M n U O i ( I I ) 3

0

is s o m e w h a t

oxygen-

deficient; the T G A d a t a suggest that the h y d r o t h e r m a l c o m p o u n d m a y c o n t a i n some o x y g e n i n excess of the t r i u r a n a t e f o r m u l a . T h e r e does n o t


222


a p p e a r to b e a n a p p r e c i a b l e s o l i d s o l u t i o n r e g i o n a b o u t the M n U a O i o ( I ) composition. I n f r a r e d . R e p r e s e n t a t i v e spectra of the d o u b l e oxides are s h o w n i n F i g u r e s 3, 4, a n d 5, a n d the a b s o r p t i o n m a x i m a of a l l fifteen phases are l i s t e d i n T a b l e s I V a n d V . A s is e v i d e n t f r o m the s p e c t r a , the i n f r a r e d results o n the 1:1 oxides are i n agreement w i t h the x - r a y d i f f r a c t i o n d a t a . T h r e e s p e c t r a l types c a n b e d i s t i n g u i s h e d . Q u a l i t a t i v e l y , the C o U 0 4


t y p e s p e c t r u m appears to represent a f o r m i n t e r m e d i a t e b e t w e e n CrU0

4

and C u U 0

4

the

s p e c t r a l types.

T h e t r i u r a n a t e spectra are r a t h e r c o m p l e x , as c o u l d be

predicted

f r o m t h e i r c o m p o s i t i o n a n d t h e i r c r y s t a l structure. W h i l e the p o w d e r d i f f r a c t i o n d a t a i n d i c a t e that the h e a v y a t o m i c f r a m e w o r k is s u b s t a n t i a l l y i d e n t i c a l i n the six t r i u r a n a t e s , the i n f r a r e d results i n d i c a t e that this is n o t t r u e for the o x y g e n a t o m locations.

T h e cobalt, n i c k e l , a n d z i n c

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

T h e exact significance of

these v a r i a t i o n s c a n o n l y b e i n t e r p r e t e d after c o m p l e t e s t r u c t u r a l i n f o r m a t i o n is a v a i l a b l e o n the c o m p o u n d s ,

b u t t h e y p r o b a b l y arise f r o m

differences i n t r a n s i t i o n e l e m e n t - o x y g e n b o n d i n g a n d the r e s u l t i n g adjust ment i n uranium-oxygen bonding.

I 900

Figure

1 800

3.

ι 700

Absorption

ι 600

cm

ι 500

ι 400

ι 300

1 200

- 1

spectra for CuUO , CrOO u

CoUO

Â9

and

u



16.

HOEKSTRA

A N D

Uranium

M A R S H A L L

1200

1000

800

Double

600

400

WAVENUMBER CM" Figure

4.

200

1

Absorption spectra for CuU O , and FeU O 3

10

223

Oxides

s

CoU 0 3

lc

10

ο

I

1300

I

1200

I

1100

I

1000

I

900

I

I

800

700

cm"

Figure

5.

Comparison

of

I

600

10

I

400

I

I

300

200

I. Hydrothermal

and

1

MnU O spectra: II. Air Ignited 3

I

500


224


Table IV. CrUO

FeOO


k

h

552 S

565 S

500 S

500 sh

412 358 350 310 280

W W W W W

432 W 370 W

238 W

235 W

330 W 278 W

Infrared Data on Monouranates

a-muoj.

MnU0

CoUO

β-NiUOj,

ZnUOj,

655 M

680 M

685 M

690 M

525 S

535 S

550 S

550 S

448 M

455 M

460 sh

455 S

515 S 456 S

350 W

345 W

345 W

340 W

358 M

292 W 250 W 223 W

290 W 277 W 221 W

298 M 265 sh 220 W

300 w 268 w 222 sh

292 W 268 M 226 W

4

560 S

430 M 342 M 264 M 220 W

h

I n general, the spectra of h y d r o t h e r m a l a n d d r y M U O i 3

0

CuUO

u

757 S

preparations

are essentially i n d i s t i n g u i s h a b l e . T h e h i g h e s t f r e q u e n c y a b s o r p t i o n m a x i m u m tends to o c c u r at a s l i g h t l y h i g h e r f r e q u e n c y

( 10-20

c m . " ) i n the 1

h y d r o t h e r m a l samples. T h i s s m a l l difference c o u l d reflect a s l i g h t o x y g e n d e f i c i e n c y i n the h i g h t e m p e r a t u r e samples.

M a n g a n e s e t r i u r a n a t e is a n

e x c e p t i o n to this r u l e since changes i n b a n d l o c a t i o n as w e l l as i n t e n s i t y are o b s e r v e d (see

T a b l e V a n d F i g u r e 5).

Table V . MnU O (I) Hydrothermal 3

868 801 748 684 652 630

10

MnU O (II) Air 3

10

849 794 750 701 665 628

S VW Sh S VW S

300 W

573 531 462 418 380 353 320 305 288

M S M W W VW W W W

243 W

258 W 240 W

S W M S S

s

570 w 510 s 387 M 362 W 327 W

FeU O Sealed tube 3

10

Infrared

CoU O Hydrothermal 3

825 S

842 M

760 S

768 W

660 S

705 S

530 S 440 S 313 M

240 W

592 S 525 S 430 S 380 s 323 w 307 w 290 w 257 w 240 w


10

16.

H O E K S T R A

A N D

Uranium

M A R S H A L L

Double

225

Oxides

A l t h o u g h d e t a i l e d s t r u c t u r a l i n f o r m a t i o n is not a v a i l a b l e for

most

of the d o u b l e oxides, correlations w h i c h h a v e b e e n e s t a b l i s h e d b e t w e e n i n f r a r e d a n d x - r a y d a t a p e r m i t a q u a l i t a t i v e i n t e r p r e t a t i o n of the s p e c t r a l results. T h e a r r a n g e m e n t of o x y g e n atoms a b o u t U ( V I ) is u s u a l l y u n s y m m e t r i c a l , w i t h t w o short p r i m a r y b o n d s a n d four, five, or six l o n g e r s e c o n d a r y b o n d s . T h e p r i m a r y b o n d s f o r m the l i n e a r u r a n y l g r o u p , w h i l e the s e c o n d a r y b o n d s l i e i n or n e a r a p l a n e n o r m a l to the u r a n y l axis


P r i m a r y b o n d lengths v a r y f r o m 1.7A. ( b o n d strength =

1).

2

2

2)

to

(23). 2.08A.

T h e d o u b l e b o n d is f o u n d i n u r a n y l salts s u c h as

U 0 F , U 0 C 0 , or N a U 0 2

( b o n d strength =

3

2

( O C O C H ) , w h i l e the single b o n d is e n 3

3

c o u n t e r e d i n the c h a i n structure of a - U 0 . M o d i f i e d u r a n y l b o n d s h a v i n g 3

b o n d strengths b e t w e e n one a n d t w o a n d b o n d lengths of 1.8 to 2 A . are f o u n d i n some u r a n y l salts a n d i n the a l k a l i a n d a l k a l i n e e a r t h uranates. T h e s e c o n d a r y b o n d s ( b o n d strength

Some Uranium-Transition Element Double Oxides - Advances in

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