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4 Bis(μ-hydroxo)tetraaquadiplutonium(IV) Sulfate Its Relation to Other Tetravalent Hydroxysulfates and to the Plutonium(IV) Polymer
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DENNIS W. WESTER Argonne National Laboratory, Chemistry Division, Argonne, IL 60439
Pu (OH) (SO ) (H O) , (I) is a hydroxysulfate which is unique among the actinides. Other members of the series form hydroxysulfates of different composition. The conditions leading to I are com pared to conditions by which hydroxysulfates of other tetravalent actinide, lanthanide and Group IVB elements are produced. The crystal structure of I is described and compared to other known hydroxysul fate structures. Hydroxysulfates of Zr, Hf and Ce are isomorphous to I. A common feature of a l l hy droxysulfates is shown to be the presence of double hydroxide bridges. Infrared, visible and near-IR spectroscopic results are compared to those for Pu(IV) polymer and indicate a close similarity be tween I and the polymer. 2
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Hydrothermal h y d r o l y s i s o f metal ions i s u s e f u l i n producing c r y s t a l l i n e phases which c o n t a i n metals i n a s t a t e o f p a r t i a l h y d r o l y s i s , i . e . , a s t a t e i n t e r m e d i a t e between t h a t o f t h e h y d r a t e d m e t a l i o n and t h a t o f t h e hydrous h y d r o x i d e . Such r e a c t i o n s h a v e b e e n u s e d t o p r o d u c e numerous c r y s t a l l i n e p h a s e s o f a c t i n i d e s (JL-4), Group I V m e t a l i o n s ( 5 - 1 4 ) a n d l a n t h a n i d e s ( 1 5 21). Previous studies o f the hydrothermal h y d r o l y s i s of t e t r a v a l e n t T h , U a n d Np ( l - _ 4 ) h a v e shown a r e m a r k a b l e s i m i l a r i t y i n t h e behavior o f these elements. I n e a c h c a s e compounds o f s t o i c h i ometry M(0H)2S0it r e p r e s e n t t h e major p r o d u c t . I n order t o extend our knowledge o f t h e h y d r o l y t i c b e h a v i o r o f t h e a c t i n i d e s and t o e l u c i d a t e s i m i l a r i t i e s a n d d i f f e r e n c e s among t h i s g r o u p o f e l e m e n t s , we h a v e i n v e s t i g a t e d t h e b e h a v i o r o f t e t r a v a l e n t p l u t o n i um u n d e r s i m i l a r c o n d i t i o n s . The r e l a t i o n s h i p s b e t w e e n t h e ma j o r product o f the hydrothermal h y d r o l y s i s o f Pu(IV), P u ( 0 H ) ( S 0 O 3 (H20)it, ( I ) , and o t h e r t e t r a v a l e n t a c t i n i d e , l a n t h a n i d e a n d Group I V B h y d r o x y s u l f a t e s a r e t h e s u b j e c t o f t h i s r e 2
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0097-6156/83/0216-0049$06.00/0 © 1983 American Chemical Society
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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port. The compounds a r e compared w i t h r e s p e c t s t r u c t u r e and s p e c t r a l p r o p e r t i e s .
to s y n t h e s i s ,
Discussion P u 2 ( 0 H ) 2 ( S 0 i t ) ( H 2 O K , ( I ) , i s an e x t r e m e l y s t a b l e p h a s e i n the P u 0 S 0 3 H 0 system. The s y n t h e s i s and c h a r a c t e r i z a t i o n o f I have been d e s c r i b e d p r e v i o u s l y (22). The r e d c r y s t a l s o f t h e com pound w e r e o b s e r v e d t o be s t a b l e i n a i r f o r a t l e a s t s i x t e e n months. 3
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Synthetic Studies. Table 1 presents the r e s u l t s of s e v e r a l hydrothermal h y d r o l y s i s reactions i n v o l v i n g various concentrations o f P u ( I V ) and s u l f a t e . T h e s e r e s u l t s s u g g e s t t h a t t h e pH o f t h e s o l u t i o n may be an i m p o r t a n t f a c t o r l e a d i n g t o t h e f o r m a t i o n o f I. I f t h e amorphous p r o d u c t i s assumed t o be an e x t e n s i v e l y h y d r o l y z e d compound, i t s f o r m a t i o n a t l o w e r pH v a l u e s w o u l d be i n h i b i t e d so t h a t t h e P u ( I V ) i o n s w o u l d r e m a i n i n s o l u t i o n and be a v a i l a b l e f o r formation of I. Such b e h a v i o r i s observed s i n c e a t s u l f u r i c a c i d c o n c e n t r a t i o n s l e s s t h a n 0.20 M o n l y t h e amorphous product i s observed. The pH v a l u e s f o r s u l f u r i c a c i d o f 0.200.25 M a r e i n t h e b o r d e r l i n e r e g i o n w h e r e t e m p e r a t u r e and c o n c e n t r a t i o n of Pu(IV) can have l a r g e e f f e c t s . For i n s t a n c e , at a con c e n t r a t i o n o f P u ( I V ) e q u a l t o 0.325 M i n 0.20 M s u l f u r i c a c i d , b o t h I and t h e amorphous p r o d u c t a r e o b s e r v e d a t 1 4 0 ° C However, r a i s i n g t h e t e m p e r a t u r e t o 180°C, w h i c h i n c r e a s e s t h e d e g r e e o f h y d r o l y s i s , c a u s e s o n l y t h e amorphous p r o d u c t t o a p p e a r . I n ano ther case, both products are observed at a Pu(IV) c o n c e n t r a i t o n o f 0.166 M and a s u l f u r i c a c i d c o n c e n t r a t i o n o f 0.25 M. Presum a b l y , an i n c r e a s e i n t h e c o n c e n t r a t i o n o f P u ( I V ) w o u l d l e a d t o a l a r g e r p r o p o r t i o n o f I due t o t h e n e c e s s i t y o f f o r m i n g d i m e r s . S u l f a t e c o n c e n t r a t i o n u n f o r t u n a t e l y p a r a l l e l e d t h a t of hydrogen i o n so t h a t t h e e f f e c t s o f c h a n g i n g s u l f a t e c o n c e n t r a t i o n w e r e o b s c u r e d . However, t h e f o l l o w i n g o b s e r v a t i o n s c a n be made. At t h e l o w e s t s u l f a t e c o n c e n t r a t i o n t h e amorphous p r o d u c t was t h e o n l y p r o d u c t o b s e r v e d . As t h e c o n c e n t r a t i o n o f s u l f a t e ( s u l f u r i c a c i d ) was r a i s e d , t h e o n l y o t h e r p r o d u c t w h i c h was o b s e r v e d was r e d c r y s t a l l i n e I . A l t h o u g h t h e g r e e n powdery amorphous p r o d u c t was o b s e r v e d up t o s u l f a t e c o n c e n t r a t i o n s o f 0.25 M, by t h e t i m e t h e s u l f a t e c o n c e n t r a t i o n r e a c h e d 0.50 M, I was t h e o n l y p r o d u c t observed a t 140°C However, s i n c e t h e f o r m a t i o n o f t h e h y d r o x y s u l f a t e s i s i n t i m a t e l y r e l a t e d t o t h e h y d r o l y s i s of the c a t i o n , we f e e l t h a t t h e pH i s t h e c o n t r o l l i n g f a c t o r . Comparison of these r e s u l t s f o r plutonium w i t h those f o r o t h e r t e t r a v a l e n t m e t a l s r e v e a l s some i n t e r e s t i n g f a c t s . Thori u m ( I V ) , u r a n i u m ( I V ) and n e p t u n i u m ( I V ) s u l f a t e s h a v e b e e n i n v e s t i g a t e d under hydrothermal h y d r o l y t i c c o n d i t i o n s . For u r a n i um, t h e s t a b l e p h a s e s w h i c h h a v e b e e n r e p o r t e d i n c l u d e U(0H)2S0it ( 2 ) , U s O ^ O H K ( S O O e ( 3 ) , U ( S 0 O * 4 H 0 (23) and U ( S 0 O (24). F o r t h o r i u m (1) and n e p t u n i u m ( 4 ) , t h e h y d r o x y s u l f a t e s M(0H) S0i+ a r e known. The c o n d i t i o n s f o r f o r m a t i o n o f t h e s e h y d r o x y s u l f a t e s 2
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Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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WESTER
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Bis(t*-hydroxo)tetraaquadiplutonium(IV) Sulfate
TABLE 1 #
H y d r o t h e r m a l H y d r o l y s i s R e a c t i o n s i n t h e Pu02*S03 H20 System
[Pu(IV)]
0.138
[S0
2 4
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0.125
T,K
140
Products
amorphous (12Pu -2S0 -7H 0) 2
3
0.325
0.20
140
amorphous + I
0.325
0.20
180
amorphous
0.166
0.25
140
amorphous + I
0.238
0.50
200
I
0.552
0.50
140
I
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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are n e a r l y i d e n t i c a l t o those f o r f o r m a t i o n o f I . F o r i n s t a n c e , f r o m u r a n i u m - c o n t a i n i n g s o l u t i o n s o f 0.1-0.5 M s u l f u r i c a c i d a t 100-150°C, U ( 0 H ) S 0 i t i s t h e p r e d o m i n a n t p r o d u c t (2). Unfortunate l y , t h e e x a c t c o n c e n t r a t i o n s o f uranium w h i c h were used a r e n o t given. A t somewhat h i g h e r u r a n i u m c o n c e n t r a t i o n s i n 0.5 M s u l f u r i c a c i d a t 200°C, U 0i» (OH) i> ( S O O i s t h e p r e d o m i n a n t p h a s e ( 3 ) . U ( S O O 2 f o r m s f r o m 0.3 M U ( I V ) i n 0.3 M s u l f u r i c a c i d a t 140°C (24). N p ( 0 H ) S 0 t f o r m s f r o m a s o l u t i o n o f 0 . 0 8 M N p ( I V ) i n 0.5 M s u l f u r i c a c i d a t 140°C ( 4 ) . ThiOH^SOt*, a l o n g w i t h o t h e r p h a s e s (one o f w h i c h may b e T h ( S 0 O · 4 H 0 ) , i s p r e p a r e d i n a s i m i l a r man ner ( 1 ) . I t i s r e m a r k a b l e t h a t i n v i e w o f t h e many d i f f e r e n t phases observed i n t h e a c t i n i d e - s u l f a t e systems, t o t h i s date t h e o n l y c r y s t a l l i n e phase w h i c h has been observed i n t h e p l u t o n i u m s u l f a t e s y s t e m i s one w h i c h i s e n t i r e l y d i f f e r e n t f r o m a l l t h e o t h e r a c t i n i d e phases. The r e a s o n s f o r t h i s d i s t i n c t i v e b e h a v i o r of p l u t o n i u m a r e a s y e t u n c l e a r e s p e c i a l l y i n v i e w o f t h e s i m i l a r i t y o f t h e f i r s t h y d r o l y s i s c o n s t a n t s f o r U, Np and P u . E x p e r iments i n v o l v i n g f u r t h e r v a r i a t i o n s o f t h e c o n d i t i o n s a r e i n pro gress. A l t h o u g h t h e phase w h i c h appears t o be v e r y s t a b l e f o r p l u t o n i u m has n o t been observed i n o t h e r A n 0 S 0 3 H 0 systems, p h a s e s o f i d e n t i c a l c o m p o s i t i o n h a v e b e e n o b s e r v e d f o r Z r , Hf and Ce. The c r y s t a l s t r u c t u r e o f t h e z i r c o n i u m compound Z r ( 0 H ) ( S O O 3 ( H 0 ) i+, i s w e l l known ( 5 ) . One v e r y i n t e r e s t i n g f e a t u r e o f t h e M 0 * S 0 3 ' H 0 s y s t e m s f o r Z r , Hf and Co i s t h a t t h e r e a r e a l a r g e number o f p h a s e s w h i c h h a v e b e e n o b s e r v e d . Some o f t h e s e c o r r e s p o n d t o p h a s e s w h i c h a r e known f o r Th, U and Np. F o r z i r c o n i u m , a s e r i e s o f b a s i c s u l f a t e s i s known t o i n c l u d e Z r ( 0 H ) (S0i+) 3 ( H 0 ) a n d two m o d i f i c a t i o n s o f Z r ( 0 H ) S 0 i t a s t h e m a j o r c o n s t i t u e n t s ( 5 ) . O t h e r b a s i c s u l f a t e s s u c h a s Z r (OH) S0if · Η 0 , ΖΓι»(ΟΗ)ιο(80θ3(Η 0)ι , Z r (OH) ( S O O ( H 0 ) and some b a s i c s u l f a t e s o f l e s s d e f i n i t e c o m p o s i t i o n a r e known ( 7 ) , b u t t h e s e a t present bear l i t t l e r e l a t i o n t o the b a s i c a c t i n i d e s u l f a t e s . I n a d d i t i o n , t h e compounds Z r ( S O O · 4 H 0 , Z r ( S O O · 1. 5 H 0 , Z r ( S 0 i * ) H 0, Z r ( S 0 O a n d Z r ( S O O 2*Η 80ι* a r e o b s e r v e d a t 100°C. (6) . The H f 0 » S 0 3 H 0 s y s t e m a l s o h a s b e e n e x t e n s i v e l y s t u d i e d . The b a s i c s u l f a t e s w h i c h a r e w e l l known i n c l u d e H f ( O H ) ( S O O 3 ( Η 0 Κ ( 1 0 ) , Ηί(0Η) 80ι* ( 1 3 ) , Hf (OH) S0i>·Η 0 ( 1 2 ) , a n d H f ( 0 H ) S O i ^ 2 H 0 ( 1 1 ) , a l t h o u g h t h e l a s t compound a l s o h a s b e e n d e s c r i b e d a s H f ^ O s ( S O O 3 · 9 H 0 ( 1 4 ) . I n a d d i t i o n , t h e compounds H f ( S 0 i + ) » X H 0 , X=0.5, 1.5 a n d 4.0 a r e known ( 1 0 ) . The p h a s e s w h i c h o c c u r i n t h e C e 0 » S 0 3 » H 0 s y s t e m a r e more numerous a n d l e s s w e l l d e f i n e d t h a n any o f t h e a b o v e m e t a l s ; h o w e v e r , o n c e a g a i n com pounds c o r r e s p o n d i n g t o C e ( 0 H ) S 0 , CeeOi* (OH) ^ ( S O O 6 a n d C e ( 0 H ) (SOO3 (H 0)M. a r e o b s e r v e d (15,16) . The c o n d i t i o n s u n d e r w h i c h t h e b a s i c s u l f a t e s o f t e t r a v a l ent, Z r , H f a n d Ce f o r m p r o v i d e a n a l o g i e s o n w h i c h t o b a s e s p e c u l a t i o n about t h e h y d r o t h e r m a l h y d r o l y s i s o f t e t r a v a l e n t p l u t o n ium. I n t h e z i r c o n i u m s y s t e m a t 100°C, t h e o n l y b a s i c s u l f a t e observed i s Z r ( O H ) ( S O O 3 ( H 0 ) , i . e . , the zirconium analog of 2
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Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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WESTER
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Bis(p-hydroxo)tetraaquadiplutonium{lV) Sulfate
I. However, as the temperature of the hydrothermal h y d r o l y s i s i s r a i s e d , two forms of Zr(0H) S04 are formed. In a d d i t i o n , Zr (OH) 2 S 0 i t » H 2 O forms from s o l u t i o n s more concentrated i n z i r c o n ium than s o l u t i o n s which produce Z r (OH) 2 (SOi*) 3 (H 0) i». Thus, i t would seem that e i t h e r higher temperatures or s o l u t i o n s more con centrated i n plutonium would produce Pu(0H)2S04 or Pu (OH) 2S04 H 0. T h i s trend seems to continue f o r the Hf02*S03 H20 system. For hafnium, the b a s i c s u l f a t e s Hf (OH) SOi»* 2H 0, Hf (OH) 2S0i* H20 and Hf(0H) S04 a r e formed a t 100, 200 and 300°C, r e s p e c t i v e l y . In a d d i t i o n , Hf 2 ( O H ) 2 ( S O O 3 ( H 2 O ) 4 i s observed a t l e a s t up to 200°C. However, f o r hafnium i t appears that H f ( O H ) 2 ( S O O 3 ( H 2 O ) 4 becomes more s t a b l e a t 200°C than Hf(OH) S04»H 0. In f a c t , the published s o l u b i l i t y diagram f o r the Hf02*S03 H20 system does not p r e d i c t the e x i s t e n c e of H f ( O H ) 2 S O 4 · H 0 a t 200°C, so that the r e s u l t s f o r the hafnium system must be i n t e r p r e t e d w i t h caution. Fortunately, f o r the Ce02*S03 H20 system the r e s u l t s a r e i n concordance w i t h the trend observed f o r the zirconium system. At temperatures up to 100°C, the p r i n c i p a l phases are 6 C e 0 * 5 S 0 1 2 H 0 , 2Ce02 3S0 * 4H 0, 3 C e 0 2 * 2 S 0 » 3 H 0 , C e 0 * S 0 · H 0, C e ( S 0 O 2 · 4 H 0 and C e ( S 0 O . As the temperature of the system i s r a i s e d , phases begin to d i s appear from the s o l u b i l i t y diagram u n t i l a t 175°C, only CeU2 S 0 * H 0 and C e ( S O O 2 remain. T h i s behavior i s s i m i l a r to that of zirconium and the same c o n c l u s i o n s w i t h respect to plutonium can be drawn. 2
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S t r u c t u r a l Studies. X-ray powder d i f f r a c t i o n p a t t e r n s f o r I i n d i c a t e that the c r y s t a l s t r u c t u r e i s isomorphous to Z r 2 ( 0 H ) 2 ~ ( S O O 3 (Η2θ)ι*. F i g u r e 1 d e p i c t s the s t r u c t u r e of the zirconium compound Ç5). The s t r u c t u r e o f I i s i d e n t i c a l to that of the zirconium analog except f o r v a r i a t i o n s i n bond d i s t a n c e s and ang l e s which do not a f f e c t the o v e r a l l s t r u c t u r e . We have as y e t been unable to o b t a i n s i n g l e c r y s t a l s of I which are s u i t a b l e f o r X-ray d i f f r a c t i o n s t u d i e s . By analogy t o the Zr compound, the s t r u c t u r e of I can be des c r i b e d as being composed of Pu2(0H)| m o i e t i e s to which are coordinated water molecules and b r i d g i n g s u l f a t e groups. Each p l u tonium i s coordinated t o eight oxygens (two hydroxide oxygens, four s u l f a t e oxygens and two water oxygens). The geometry of the c o o r d i n a t i o n sphere i s dodecahedral. In the absence of data obt a i n e d from a s i n g l e c r y s t a l s t r u c t u r a l a n a l y s i s , more d e t a i l e d d i s c u s s i o n of the c o o r d i n a t i o n sphere i s not p o s s i b l e . The c r y s t a l s t r u c t u r e s of H f ( O H ) ( S O 4 ) 3 ( H 0 ) 4 ( 1 4 ) and C e 2 (OH) 2 ( S O O 3 ( H 2 O K ( 1 4 ) a l s o have been determined and found to be isomorphous to the zirconium compound. The c e l l constants f o r t h i s s e r i e s of four isomorphous compounds r e f l e c t the e f f e c t of the i o n i c r a d i i on the dimensions of the u n i t c e l l . The v a l u e s f o r these c e l l constants are i n Table I I . Thus, the c e l l cons t a n t s f o r the zirconium and hafnium compounds are n e a r l y i d e n t i c a l and smaller than the c e l l constants f o r the cerium and p l u tonium compounds which are a l s o n e a r l y i d e n t i c a l . This trend i s e x a c t l y that followed by the i o n i c r a d i i of these elements. +
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Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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Figure 1. The crystal structure of Z r ( 0 H ) ( S 0 ) ( H 0 ) , reprinted with permission from Ref. 5, copyright 1966, American Chemical Society. Zirconium atoms are shown as solid c i r c l e s , oxygen atoms as open c i r c l e s . The Pu compound is isomorphous, Zr being replaced by Pu. la shows the manner in which the bridging sulfates link Pu atoms to form layers, lb shows the manner in which layers are linked through the double hydroxide bridges. 2
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Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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4.
WESTER
Bis(fi-hydroxo)tetraaquadiplutonium(IV) Sulfate
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TABLE I I Cell M =
a (A) b(A) c(A)
C o n s t a n t s f o r M ( 0 H ) (so ) 2
Zr
13.056
2
4
3
-4H 0 2
Hf
Ce
Pu
13.1
13.5
13.51
6.5
6.7
6.71
15.092
15.1
15.8
15.52
96.35
96.5
91
95.7
6.5075
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
56
PLUTONIUM
Comparison of the c r y s t a l s t r u c t u r e f o r the M ( O H ) ( S O ^ ) 3 (H 0)it s e r i e s o f compounds (M=Zr,Hf,Ce,Pu) w i t h the c r y s t a l s t r u c t u r e of other h y d r o x y s u l f a t e compounds r e v e a l s a common s t r u c t u r a l f e a t u r e which pervades the chemistry of these h y d r o l yzed s p e c i e s . The e x i s t e n c e o f - M ( O H ) Μ - · moieties i n nearly a l l of the h y d r o x y s u l f a t e s t r u c t u r e s which have been determined i s i n deed very s t r i k i n g . For the s e r i e s of compounds M(0H) S04, where M=Zr ( 1 4 ) , Hf U 3 ) , Th (1 ) , U ( 2 ) and Np (_4), the metal atoms are l i n k e d i n t o chains through the b r i d g i n g hydroxides. F i g u r e 2 shows the s t r u c t u r e of the compound Th(OH) SOit from s e v e r a l view p o i n t s . The metal atoms form z i g z a g a r r a y s , w i t h two hydroxide l i g a n d s s e p a r a t i n g one metal from the next. Thus, the s t o i c h i o metry of the chains i s [M(OH) ]£ . C r y s t a l s t r u c t u r e s f o r Μ ( Ο Η ) 8 θ 4 · Η 0 where M=Zr (8), Hf (12) a l s o have been determined and r e v e a l the presence o f almost p l a n a r z i g z a g chains o f metal atoms j o i n e d by double hydroxide b r i d g e s . The s i n g l e exception to t h i s trend toward formation of double hydroxy-bridged metal dimers o r chains i s the compound which i s best d e s c r i b e d as CeOSOit H 0 ( 1 7 ) . However, even i n t h i s s t r u c t u r e the cerium ions form chains which are l i n k e d by b r i d g i n g oxide i o n s . Accommodation o f metal atoms o f widely d i f f e r i n g i o n i c r a d i i i n t o the same o v e r a l l s t r u c t u r e c r e a t e s i n t e r e s t i n g p o s s i b i l i t i e s f o r the doping of metal ions i n t o a common matrix f o r s p e c t r o s c o p i c examination under n e a r l y constant c r y s t a l f i e l d e f f e c t s . For i n s t a n c e , o b s e r v a t i o n o f i d e n t i c a l phases f o r zirconium and plutonium i n d i c a t e that the zirconium compound would serve as a s u i t a b l e matrix i n which t o i s o l a t e plutonium. S i m i l a r l y , the appearance of i d e n t i c a l phases f o r Th, U and Np makes p o s s i b l e the doping of uranium or neptunium i n t o a thorium matrix. H y d r o l y s i s of t e t r a v a l e n t plutonium leads u l t i m a t e l y to a s p e c i e s d e s c r i b e d as Pu(IV) polymer ( 2 5 - 2 7 ) . Although t h i s spe c i e s i s s o l u b l e , i t s s t r u c t u r e has eluded d e t e c t i o n . Due to the predominance o f double hydroxy-bridged dimeric metal c l u s t e r s i n the s t r u c t u r a l chemistry o f t e t r a v a l e n t Zr, Hf, Ce, Th, U , Np and Pu; i t i s p l a u s i b l e t o suggest that the i n i t i a l step i n the f o r mation of the Pu(IV) polymer may be the h y d r o l y s i s of aqueous Pu(IV) to form hydroxy-bridged dimers. Further steps may be r e l a t e d to those observed i n zirconium h y d r o l y s i s . As mentioned p r e v i o u s l y , s p e c i e s such as Zri* (OH)i 0 (SOi+) 3 (H 0) 1 0 c o n t a i n i n g c y c l i c tetramers of oxide-bridged zirconium atoms have been as signed to these slowly hydrolyzed s p e c i e s , but f i n a l c o n f i r m a t i o n of the s t r u c t u r e s of both the zirconium and plutonium polymers i s l a c k i n g . However, u s i n g t y p i c a l i n t e r a t o m i c d i s t a n c e s from c r y s t a l l o g r a p h i c s t r u c t u r e determinations, the r a d i u s of such t e t r a meric c l u s t e r s would be on the order of 14 A, a dimension vtfiich agrees remarkably w e l l w i t h the dimension of the primary p a r t i c l e s o f Pu(IV) polymer as determined from e l e c t r o n micrographs (25). 2
2
2
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CHEMISTRY
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Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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4.
WESTER
Bis(p-hydroxo)tetraaquadiplutonium(IV) Sulfate
Th
57
OH
y
ζ
Figure 2.
The crystal structure of Th(0H) S0 , reprinted with 2
4
permission from Réf. 1, copyright 1950, Royal Swedish Academy of Science. The -M(0H) M- moiety is shown in the upper l e f t . 9
The (M(0H)^]
2
zigzag chain is illustrated in the upper right
The bottom views show how the zigzag chains are linked by bridging sulfate groups.
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
58
PLUTONIUM CHEMISTRY
Spectroscopic Studies. Comparison o f t h e i n f r a r e d spectrum o f I w i t h t h a t f o r t h e M(0H) S0it compounds, where M=U,Np, r e v e a l s t h e e x p e c t e d d i f f e r e n c e s and s i m i l a r i t i e s . The i n f r a r e d s p e c t r u m o f I i s shown i n F i g u r e 3 . The p r e s e n c e o f w a t e r o f c o o r d i n a t i o n i n _ t h e s t r u c t u r e o f I g i v e s r i s e t o b a n d s a t ^ 3 2 0 0 cm" a n d 1600 cm . Since such water molecules a r e absent i n t h e s t r u c t u r e o f t h e M ( 0 H ) S 0 i compounds, t h e s e b a n d s a l s o a r e a b s e n t i n t h e i n f r a r e d s p e c t r u m o f t h e M(0H) S0it compounds. On t h e o t h e r h a n d , b r i d g i n g s u l f a t e g r o u p s a r e common t o b o t h s t r u c t u r e s a n d t h e s u l f a t e r e g i o n o f t h e i n f r a r e d spectrum, ^1300-1000 cm" , i s s u r p r i s i n g l y s i m i l a r f o r b o t h t y p e s o f compounds. P l u t o n i u m ( I V ) p o l y m e r h a s b e e n examined b y i n f r a r e d s p e c t r o s copy ( 2 6 ) . One o f t h e p r o m i n e n t f e a t u r e s i n t h e i n f r a r e d s p e c t r u m o f t h e p o l y m e r i s a n i n t e n s e b a n d i n t h e OH s t r e t c h i n g r e g i o n a t ^ 3 4 0 0 cm . Upon d e u t e r a t i o n , t h i s band s h i f t s t o ^ 2 4 0 0 cm . However, i t c o u l d n o t b e p o s i t i v e l y a s s i g n e d t o OH v i b r a t i o n s i n t h e p o l y m e r due t o a b s o r p t i o n o f w a t e r b y t h e K B r p e l l e t . I n v i e w o f t h e b r o a d band o b s e r v e d i n t h i s same r e g i o n f o r I , i t now seems l i k e l y t h a t t h e bands o b s e r v e d p r e v i o u s l y f o r P u ( I V ) p o l y mer a r e a c t u a l l y due t o OH i n t h e p o l y m e r . I n d e e d , we h a v e o b s e r v e d a s i m i l a r s h i f t i n t h e s h a r p a b s o r p t i o n o f U ( 0 H ) S 0 i * upon d e u t e r a t i o n ( 2 8 ) . T h i s a b s o r p t i o n s h i f t s f r o m ^ 3 5 0 0 cm t o ^ 2 6 0 0 cm . V i s i b l e a n d n e a r - I R s p e c t r a o f I a r e shown i n F i g u r e s 4 a n d 5, r e s p e c t i v e l y . Both regions o f t h e s p e c t r a a r e d i s t i n c t i v e due t o t h e s h a r p n e s s a n d abundance o f a b s o r p t i o n s . A t t h i s time a d e t a i l e d a n a l y s i s o f t h e spectrum o f I has n o t been c a r r i e d out. However, q u a l i t a t i v e c o m p a r i s o n w i t h some s p e c t r a o f P u ( I V ) compounds does r e v e a l some i n t e r e s t i n g r e l a t i o n s h i p s . The v i s i b l e s p e c t r u m o f P u i S O t , ) · 4 H 0 a t - 9 2 ° C (29) a l s o shows numerous s h a r p a b s o r p t i o n s b e t w e e n ^ 7 0 0 - 4 0 0 nm. A l t h o u g h Pu(S0i+) 2* 4 H 0 e x i s t s i n two p o l y m o r p h i c f o r m s , b o t h f o r m s c o n t a i n e i g h t c o o r d i n a t e p l u t o n i u m i n a s i t e symmetry s i m i l a r t o t h e Dt+d s i t e o f p l u t o n i u m i n I . Thus, e v e n t h o u g h t h e f o r m o f P u ( S 0 i + ) 4 H 0 w h i c h was u s e d f o r t h e s p e c t r o s c o p i c s t u d y i s n o t s p e c i f i e d , we c a n assume t h a t t h e s i t e symmetry o f p l u t o n i u m i s s i m i l a r t o t h a t i n I . I n t h e r e g i o n 6 0 0 - 7 0 0 nm, b o t h s p e c t r a a r e c h a r a c t e r i z e d by a s e r i e s o f t h r e e a b s o r p t i o n s . I n a d d i t i o n , an absorption o c c u r s a t ^ 7 1 0 - 7 2 0 nm f o r e a c h compound, b u t t h a t f o r I shows much more f i n e s t r u c t u r e i n t h i s r e g i o n . E a c h s p e c t r u m h a s two v e r y s h a r p a b s o r p t i o n s n e a r 575 nm w h i c h a r e f o l l o w e d b y b r o a d a b s o r p t i o n s n e a r 540 nm. F e a t u r e s o f t h e s p e c t r a a t h i g h e r e n e r g i e s a r e a l s o v e r y s i m i l a r a n d may b e i n d i c a t i v e o f P u ( I V ) i n s i t e symmetry a p p r o a c h i n g Di+d, i - e . , a n A r c h i m e d e a n a n t i p r i s m . Near-IR and v i s i b l e s p e c t r a o f t h e Pu(IV) polymer have been published (27). Although the spectra generally are very broad, t h e a b s o r p t i o n s c o r r e s p o n d w e l l t o t h e f a m i l i e s o f peaks seen f o r I . E s p e c i a l l y n o t a b l e a r e f e a t u r e s b e t w e e n 1 0 0 0 - 1 2 0 0 nm a n d 6 0 0 - 7 0 0 nm. I n e a c h c a s e , t h e s p e c t r u m o f I r e s e m b l e s t h a t o f 2
1
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Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Figure 4. Visible spectrum of I, reprinted with permission from Ref. 22, copyright 1982, American Chemical Society.
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Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Figure 5. Near-IR spectrum of I, reprinted with permission from Ref. 22, copyright 1982, American Chemical Society.
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62
PLUTONIUM CHEMISTRY
the polymer, except that numerous sharp peaks are superimposed on what would correspond to the broad absorptions of the polymer. Gaseous PuCli* at 928°C has been examined spectroscopically (30). Comparison of its spectrum with that of I once again shows similarities although the relatively broad peaks in the spectrum of PuClif which correspond to the families of peaks in the spec trum of I are shifted to lower energies. The fact that the spec tra of Pu(IV) are similar under such widely differing conditions suggests that these transitions may be insensitive to the en vironment of the central atom. Conclusions We have investigated the hydrothermal hydrolytic behavior of Pu(IV) sulfate solutions in the temperature range 140-200°C The only crystalline phase which has been isolated has the formula Pu2 (OH) 2 (SOO 3 (H2OK. The appearance of this phase is quite re markable because under similar conditions the other actinides which have been examined form phases of different composition (Μ(0Η)280ί*, M=Th,U,Np). Thus, plutonium apparently lies at that point in the actinide series where the actinide contraction in fluences the chemistry such that elements in identical oxidation states will behave differently. The chemistry of plutonium in this system resembles that of zirconium and hafnium more than that of the lighter tetravalent actinides. Structural studies do reveal a common feature among the various hydroxysulfate com pounds, however, i . e . , the existence of double hydroxide bridges between metal atoms. This structural feature persists from zir conium through plutonium for compounds of stoichiometry Μ(0Η)280ι* to Μ2(0Η)2(50θ 3 (Η 2 0)ι*. Spectroscopic studies show similarities between Pu2 (OH) 2 (S0i+) 3 (H20) t* and the Pu(IV) polymer and suggest that common structural features may be present. Ac knowledgment This work was performed under the auspices of the Office of Basic Energy Sciences, Division of Nuclear Sciences, U. S. Depart ment of Energy under contract number W-31-109-ENG-38. Literature Cited 1. 2. 3. 4. 5. 6. 7.
Lundgren, G. Ark. Kemi 1950, 2, 535. Lundgren, G. Ark. Kemi 1952, 4, 421. Lundgren, G. Ark. Kemi 1953, 5, 349. Wester, D.W.; Mulak, J.; Banks, R.; Carnall, W.T. in press. McWhan, D. B.; Lundgren, G. Inorg. Chem. 1966, 5, 284. Motov, D.L.; Ritter, M.P. Russ. J. Inorg. Chem. 1968, 13, 1339. Chekmarev, A.M.; Molokanova, L.G.; Kharlambus, L.P.; Yagodin, G.A. Russ. J. Inorg. Chem. 1978, 23, 1474.
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
4. WESTER 8. 9. 10.
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11. 12. 13. 14. 15. 16. 17. 18.
19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30.
Bis(iJL-hydroxo)tetraaquadiplutonium(IV) Sulfate 63
Hansson, M. Acta Chem. Scand. 1973, 27, 2614. Vinarov, I.V.; Kovaleva, E.I. Russ. J. Inorg. Chem. 1968, 13, 1024. Motov, D.L.; Ritter, M.P. Russ. J. Inorg. Chem. 1968, 13, 879. Hansson, M.; Lundgren, G. Acta Chem. Scand. 1968, 22, 1683. Hansson, M. Acta Chem. Scand. 1969, 23, 3541. Hansson, M. Acta Chem. Scand. 1973, 27, 2455. Rogachev, D.L.; Antsyshkina, A.S.; Porai-Koshits, M.A. Zh. Strukt. Khim. 1972, 13, 260. Trofimov, G.V.; Belokoskov, V.I. Russ. J. Inorg. Chem. 1968, 13, 135. Trofimov, G.V. Russ. J. Inorg. Chem. 1968, 13, 1457. Lundgren, G. Ark. Kemi 1954, 6, 59. Fahey, J.A.; Williams, G.J.B.; Haschke, J.M. "The Rare Earths in Modern Science and Technology"; McCarthy, G.J., Rhyne, J.J., Silber, H.B. Eds.; Plenum: New York, 1980, Vol. 2, 181. Lance-Gomez, E.T.; Haschke, J.M.; Butler, W.; Peacor, D.R. Acta Crystallogr. 1978, B34, 758. Lance-Gomez, E.T.; Haschke, J.M. J. Solid State Chem. 1978, 23, 275. Haschke, J.M.; Eyring, L. Inorg. Chem. 1971, 10, 2267. Wester, D.W. Inorg. Chem. 1982, 21, 3382. Kierkegaard, P. Acta Chem. Scand. 1956, 10, 599. Aldred, A.T.; Koprowicz, L.; Mulak, J.; Weglowski, S.; Wrobel, B. Proc. 11th Journees des Actinides 1981, p. 169. Lloyd, M.H.; Haire, R.G. Radiochim. Acta 1978, 25, 139. Toth, L.M.; Friedman, H.A. J. Inorg. Nucl. Chem. 1978, 40, 807. Costanzo, D.A.; Biggers, R.E.; Bell, J.T. J. Inorg. Nucl. Chem. 1973, 35, 609. Baran, B.; Wester, D.W., personal communication. Leontovich, A.M. Opt. Spektrosk. 1957, 2, 695. Gruen, D.M.; DeKock, C.W. J. Inorg. Nucl. Chem. 1967, 29, 2569.
RECEIVED December
21,1982
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
