A v e r y large n u m b e r of actinide(IV) fiuoro complexes h a v e b e e n identified, p r e p a r e d b y p r e c i p i t a t i o n from a q u e o u s solution or b y h e a t ing t o g e t h e r t h e c o m p o n e n t salts. T h e simplest of these are of t h e form A^M^^Fg; w h e n o b t a i n e d from a q u e o u s solution t h e y are s o m e t i m e s p r e c i p i t a t e d as t h e m o n o h y d r a t e s , b u t t h e h y d r a t i o n w a t e r is e v i d e n t l y held only v e r y w e a k l y since t h e a n h y d r o u s salts h a v e often b e e n r e p o r t e d w h e n a p a r t i c u l a r p r e p a r a t i o n h a s been r e p e a t e d w i t h slightly m o r e s t r i n g e n t d r y i n g conditions. Some of these salts are listed in T a b l e I X . Some salts are also o b t a i n e d b y h e a t i n g t h e actinide dioxides w i t h a m m o n i u m fluoride or bifluoride a t m o d e r a t e t e m p e r a t u r e s ; in t h e re
action w i t h u r a n i u m dioxide (Van I m p e , 1954) t h e complex NH4UOF3 a p p e a r s t o be formed initially, a n d t h e c o m p o u n d s (NH4)2UF6 a n d NH4U2F9 are formed a t a b o u t 390° ( N e u m a n n et al., 1962). P l u t o n i u m dioxide r e a c t s a t 125° (Maly et al., 1961; Tolley, 1954). T h e i n t e r m e d i a t e h y d r a t e s which can be isolated are readily d e h y d r a t e d a t a b o u t 150°
330 κ . w . BAGNALL
A M C o l o u r H2O R e f e r e n c e s
N a T h W h i t e 1 T a n a n a e v a n d L u C h z h a o - D a ( 1 9 5 9 a )
K T h W h i t e —a Z a c h a r i a s e n ( 1 9 4 8 a ) .
N a , K U G r e e n — Z a c h a r i a s e n ( 1 9 4 8 a )
N a u G r e e n 1 T a n a n a e v et al. (1962)
N H 4 u G r e e n — R o d r i g u e z et al. (1958) N H 4, N a u G r e e n — S c h u l z etal. (1958) Ν 2 Η 5 + , Ν Η 2 θ Η + T h ; U W h i t e ; g r e e n — S a h o o a n d P a t n a i k (1961) N H 4 N p B r i g h t g r e e n — L a C h a p e l l e et αΖ. (1949) N a , K , R b P u G r e e n — A n d e r s o n ( 1 9 4 9 a ) ; A l e n c h i k o v a
et al. ( 1 9 5 8 b )
L i , N a , P u G r e e n — S e a b o r g (1960)
K , R b , C s
N a P u G r e e n — D e i c h m a n n a n d T a n a n a e v (1961)
a K T h F g. H a O a n d R b T h F g. S H g O h a v e a l s o b e e n r e p o r t e d ; t h e s a m e p a p e r d e s c r i b e s t h e p r e p a r a t i o n o f a n h y d r o u s K T h F g b y h e a t i n g t h o r i u m t e t r a f l u o r i d e w i t h a n e x c e s s o f p o t a s s i u m fluoride, t h e l a t t e r b e i n g r e m o v e d b y w a s h i n g w i t h w a t e r ( R o s e n h e i m et al., 1903).
(U(IV) ) or 200° ( P u ( I V ) ). T h e only pentafluoroamericmm(IV) salt k n o w n is K A m P g , m a d e b y t h e a c t i o n of fluorine on p o t a s s i u m ameri
cium (V) c a r b o n a t e (Asprey, 1954).
I n a d d i t i o n t o t h e simple pentafluorocomplex salts, a v a r i e t y of salts of composition 7M^F.6M^^F4 h a v e been r e p o r t e d a n d , from considera
t i o n of t h e cation r a d i u s ratios M+/M^+, a n u m b e r of fluoro complexes h a v e been p r e d i c t e d for s y s t e m s which h a v e n o t y e t been i n v e s t i g a t e d (Thoma, 1962). A single crystal s t u d y ( B r u n t o n , 1966) of t h e complex originally r e p o r t e d a s 7LiF.6UF4 (Harris et al., 1959) h a s shown it t o b e LiUFg, a n d since this is isostructural w i t h ''7LiF.6ThF4" (Harris et al.,
1959), t h e c o m p o u n d m u s t b e LiThFg. T h e 7:6 stoicheiometry does exist, however, where t h e r a t i o lies b e t w e e n 0-99 a n d 1-68 a n d all such sodium, p o t a s s i u m , a m m o n i u m , a n d r u b i d i u m salts a r e of r h o m b o h e d r a l s y m m e t r y . This suggests t h a t K T h F ^ , KUF5, K P u F g , N a U F g , N a P u F g a n d R b U F g a r e really t h e 7:6 c o m p o u n d s . I t h a s been p r e dicted (Thoma, 1962) t h a t stable 7:6 a n d 1:1 complexes will b o t h exist w h e r e M+/M^+ lies b e t w e e n 1-59 a n d 1-68; e x a m p l e s a r e R b U F g a n d 7RbF.6UF4 ( T h o m a et al., 1958) a n d t h e analogous a m m o n i u m salts (Benz et al, 1963).
Salts of t h e t y p e A^M^^Fg a r e also o b t a i n e d from a q u e o u s solution (Table X ) a n d w i t h a n excess of alkali fluoride t h e q u a d r i v a l e n t actinides yield fluorides of t h e t y p e AaMi^Fg ( T h — R o s e n h e i m et al, 1903;
T a n a n a e v a n d L u Chzhao-Da, 1959b; P u (pink N a a n d NH4 salts)—
Alenchikova et al, 1958b). (NH4)2UF6,(NH4)4UF8 a n d species such a s
TABLE I X . F l u o r o c o m p l e x e s o f t h e t y p e A ^ M ^ ^ F s
T H E H A L O G E N C H E M I S T R Y O F T H E A C T I N I D E S 331
A M C o l o u r H2O R e f e r e n c e s
N a , K T h W h i t e » — Z a c h a r i a s e n ( 1 9 4 8 a )
K, N H 4 T h W h i t e — T a n a n a e v a n d L u C h z h a o - D a ( 1 9 5 9 b )
Κ u G r e e n — Z a c h a r i a s e n ( 1 9 4 8 a )
Κ N p G r e e n — L a C h a p p e l l e et al. (1949)
Κ P u P i n k — S e a b o r g (1960)
C s P u L i g h t r e d - 3H2O A n d e r s o n ( 1 9 4 9 a ) ; A l e n c h i k o v a
b r o w n et al. ( 1 9 5 8 b )
a K T h g F g. e H a O h a s a l s o b e e n r e p o r t e d ( R o s e n h e i m et al., 1 9 0 3 ) .
7NH4P.6UF4 h a v e also b e e n o b t a i n e d from a q u e o u s solution (Penne-m a n et al., 1964a). T h e p r o t a c t i n i u (Penne-m c o (Penne-m p o u n d , 7 R b P. 6 P a F 4 , h a s been m a d e b y h e a t i n g R b P a ^ P ^ in h y d r o g e n a t 450° (Asprey et al., 1965b).
T h e americium(IV) hexafluoro complex, RbgAmPg, a n orange-pink solid, h a s been m a d e b y t r e a t i n g a m e r i c i u m ( I V ) h y d r o x i d e w i t h I M hydrofluoric acid s a t u r a t e d w i t h r u b i d i u m fluoride or b y a d d i n g 12M r u b i d i u m fluoride t o a solution of r u b i d i u m americium(V) c a r b o n a t e i n
I M nitric acid a n d allowing t h e m i x t u r e t o s t a n d o v e r n i g h t (Kruse a n d Asprey, 1962), t h e r e d u c t i o n p r e s u m a b l y being d u e t o t h e p r o d u c t s of t h e a-radiolysis of t h e solvent. Stable a q u e o u s solutions of a m e r i c i u m ( I V ) are o b t a i n e d b y t r e a t i n g a m e r i c i u m ( I V ) h y d r o x i d e w i t h s a t u r a t e d a q u e o u s a m m o n i u m fluoride; t h e r e d solid p h a s e in equilibrium w i t h t h e solution is t h e octafluorocomplex salt, (NH4)4AmF8. Sparingly soluble fluorocomplex salts a r e also o b t a i n e d w i t h p o t a s s i u m , r u b i d i u m a n d caesium fluorides in place of a m m o n i u m fluoride, b u t t h e i r com
positions h a v e n o t b e e n r e p o r t e d (Asprey a n d P e n n e m a n , 1962).
A few alkaline e a r t h hexafluorometallates(IV) a r e also k n o w n ; CaUFe.HaO p r e c i p i t a t e s from a q u e o u s solution a n d d e h y d r a t e s r e a d i l y w i t h o u t hydrolysis a t 250-300° in argon (Tolley, 1959). T h e s t r u c t u r e s of t h e alkaline e a r t h a n d lead hexafluorothorates(IV) a n d u r a n a t e s ( I V ) , p r e p a r e d b y h e a t i n g t h e c o m p o n e n t salts t o g e t h e r , h a v e been r e c o r d e d (Zachariasen, 1949a) a n d some aspects of t h e SrThFg a n d B a U F g s y s t e m s h a v e been i n v e s t i g a t e d ( D ' E y e a n d F e r g u s o n , 1959).
T h e solid phases i n equilibrium w i t h a q u e o u s hydrofluoric acid of v a r y i n g c o n c e n t r a t i o n h a v e , in t h e case of t h e t h o r i u m tetrafluoride s y s t e m , b e e n identified a s ThF4.HF.H2O ( 3 5 · 2 - 7 0 · 7 % H F ) a n d ThF4.4HF ( 7 5 - 9 0 - 3 % H F ) , w h e r e a s t h e soHd p h a s e i n c o n t a c t w i t h dilute hydrofluoric acid is ThF4.0-7-l-5H2O (Buslaev a n d G u s t y a k o v a , 1965). T h e hexafluorometallate ion is p r o b a b l y p r e s e n t in solutions of t h e tetrafluorides i n 15M a m m o n i u m ( P a ( I V ) — H a i s s i n s k y et al., 1 9 6 1 ;
TABLE X . F l u o r o c o m p l e x e s o f t h e t y p e A i M / F \
332 κ . w. BAGNALL
Am(IV)—^Asprey a n d P e n n e m a n , 1961) or caesium (Cm(IV)—Keenan 1961) fluoride.
All of t h e a n h y d r o u s species o b t a i n e d from a q u e o u s solution, a n d a large n u m b e r of o t h e r fluoro complexes, h a v e been identifled in fused salt systems, n o t a b l y CsF-ThF4 ( T h o m a a n d Carlton, 1961), L i F a n d N a F- T h F 4 ( T h o m a et al, 1959a), K F- T h F 4 (Asker et al, 1952) a n d N a F a n d K F- T h F 4 ( K a p l a n , 1955); t h e u r a n i u m tetrafluoride s y s t e m s ( N a F - L i F- U F 4 ( T h o m a et al, 1959b), L i F a n d N a F- U F 4 ( B a r t o n et al, 1958), K F a n d R b F- U F 4 ( T h o m a et al, 1958) h a v e also been t h o r o u g h l y investigated. T h e s y s t e m L i F- T h F 4- U F 4 contains a m i x t u r e of fluoro complexes which form a c o n t i n u o u s series of solid solutions, as do ThF4 a n d UF4 (Weaver et al, 1959).
Crystallographic studies of t h e p r o d u c t s o b t a i n e d b y h e a t i n g t h e actinide tetrafluorides w i t h alkali m e t a l fluorides in v a r y i n g p r o p o r t i o n s h a v e shed a g r e a t deal of light on t h e n a t u r e of t h e species which can be formed; t h e principal s y s t e m s i n v e s t i g a t e d include N H 4 F - U F 4 a n d PUF4 (Benz et al, 1963) a n d N H 4 F - P a F 4 (Asprey a n d P e n n e m a n , 1965), in which octafluorometallates(IV) h a v e been o b t a i n e d , N a F a n d K F- T h F 4 a n d UF4 (Zachariasen, 1948a), L i F-ThF4 (Harris et al, 1959) a n d N a F- T h F 4 a n d UF4 ( T h o m a et al, 1963).
T h e halo complexes formed b y halogens of higher a t o m i c n u m b e r are increasingly less stable, indicating t h e essentially A - t y p e c h a r a c t e r of t h e actinides. T h e species formed are also m u c h simpler t h a n in t h e case of t h e fluoro complexes, almost i n v a r i a b l y being of t h e t y p e AgM^^Xg.
T h u s t h e chloro complexes isolated from a q u e o u s solution are usually of this form, b u t t h e p r o c e d u r e is only suitable for t h e p r e p a r a t i o n of salts of t h e larger unipositive cations because of t h e lower solubility of t h e halocomplex salts formed b y t h e m ; some e x a m p l e s are given in T a b l e X I .
T h e pale green sodium (Moissan, 1896), p o t a s s i u m a n d lithium salts, A^gUCle, a n d calcium, s t r o n t i u m a n d b a r i u m salts, A^UCle, h a v e been m a d e b y passing u r a n i u m t e t r a c h l o r i d e v a p o u r over t h e alkali or alkaline e a r t h chloride a t r e d h e a t (Aloy, 1899, 1901b). N o n a q u e o u s solvents also provide a convenient r o u t e t o t h e h e x a h a l o complexes;
t e t r a e t h y l a m m o n i u m h e x a c h l o r o t h o r a t e( I V ) , which exists in t w o crystal modifications (Brown, 1966), a n d u r a n a t e( I V ) h a v e been m a d e b y mixing t h i o n y l chloride solutions of t h e a p p r o p r i a t e t e t r a c h l o r i d e a n d t e t r a e t h y l a m m o n i u m chloride, e v a p o r a t i n g t h e solvent a n d precipitat
ing t h e complex w i t h acetic a n h y d r i d e (Adams, D . M. et al, 1963) a n d these salts, a n d t h e corresponding t e t r a m e t h y l a m m o n i u m c o m p o u n d s , are also easily m a d e from m e t h y l c y a n i d e solution (Brown, 1966; Feltz, 1966), from which t h e y crystallize w h e n t h e solution is cooled in ice.
T H E H A L O G E N C H E M I S T R Y O F T H E A C T I N I D E S 333
TABLE X I . C h l o r o c o m p l e x e s o f t h e t y p e AjM^^ Clg p r e p a r e d f r o m a q u e o u s s o l u t i o n
A M C o l o u r R e f e r e n c e s
N H 4, L i T h W h i t e C h a u v e n e t ( 1 9 0 9 , 1 9 1 1 ) NTa, R b , C s
p y H , q u i n H a T h W h i t e R o s e n h e i m et al. ( 1 9 0 3 ) ; R o s e n h e i m a n d S c h i l l i n g (1900)
C s T h W h i t e F e r r a r o (1957)
C s P a G r e e n B r o w n a n d J o n e s ( 1 9 6 7 b )
Cs, N M e 4 , N E t 4 U G r e e n D i e k e a n d D u n c a n i > ( 1 9 4 9 ) ; F e r r a r o (1957) ΝΜθ4, N E t 4 U G r e e n S t a r i t z k y a n d S i n g e r (1952)
P y H * U G r e e n R o s e n h e i m a n d K e l m y d (1932)
R g P H C U G r e e n G a n s a n d S m i t h ( 1 9 6 3 , 1 9 6 4 a )
C s N p Y e l l o w B a g n a l l et al. ( 1 9 6 1 )
N E t 4 N p Y e l l o w R y a n ( 1 9 6 1 ) C s, N E t 4 , P u Y e l l o w A n d e r s o n ( 1 9 4 9 b ) p y H j q u i n H »
N M e 4 , N E t 4 P u Y e l l o w S t a r i t z k y a n d S i n g e r ( 1 9 5 2 ) Net4 P u Y e l l o w R y a n ( 1 9 6 1 )
C s P u Y e l l o w M i n e r et al. ( 1 9 6 3 )
* p y , p y r i d i n e ; q u i n , q u i n o l i n e . P r e p a r e d f r o m a l c o h o l i c h y d r o c h l o r i c a c i d s o l u t i o n .
^ T h e s e c o m p o i m d s a r e n o t a s s u s c e p t i b l e t o o x i d a t i o n a s t h e a u t h o r s s t a t e .
*5 F r o m e t h a n o l i c s o l u t i o n .
^ D i h y d r a t e .
T h e m e t h o d h a s also b e e n used for t h e p r e p a r a t i o n of t h e analogous p r o t a c t i n i u m ( I V ) hexachloro complexes, for which t h i o n y l chloride can
n o t b e used since it oxidizes p r o t a c t i n i u m ( I V ) (Brown a n d J o n e s , 1966c, 1967b). T h e Th—Cl, U — C l (Brown, 1966) a n d N p — C l (Brown, 1966;
Bagnall a n d Laidler, 1966) v i b r a t i o n s in t h e infrared s p e c t r a of t h e h e x a c h l o r o m e t a l l a t e s ( I V ) a p p e a r a t a b o u t 253 cm-^, 253-259 c m - ^ a n d 267 c m- i respectively.
T h e h y d r a t e d p o t a s s i u m enneachloro complex, KThaClg (Clève, 1874) a n d h y d r a t e d p e n t a c h l o r o t h o r a t e s ( I V ) , A^ThClg (A = Li, Na,K,NH4) a n d h e x a c h l o r o t h o r a t e s ( I V ) , AigThClg (A = Rb,Cs,NH4) h a v e been o b t a i n e d from a q u e o u s solution (Chauvenet, 1909). H y d r a t e d a m m o n i u m h e x a c h l o r o t h o r a t e ( I V ) yields NH4ThCl5 o n h e a t i n g , a n d t h e h y d r a t e d r u b i d i u m a n d caesium salts c a n b e d e h y d r a t e d b y h e a t i n g i n h y d r o g e n chloride a t 150°, w h e r e a s t h e lithium, sodium a n d p o t a s s i u m salts form complexes of t h e t y p e AiTh(0H)Cl4 a t 200° a n d AThOClg a t a b o u t 400°
(Chauvenet, 1909). T h e a n h y d r o u s h e x a c h l o r o t h o r a t e s ( I V ) , AigThClg (A = Li, N a , K , Rb,Cs) a n d octachlorothorates(IV), Ai4ThCl8 (A = R b , Cs) a r e r e p o r t e d t o b e formed b y fusing t o g e t h e r t h e stoicheiometric q u a n t i t i e s of alkali halides a n d t h o r i u m t e t r a c h l o r i d e ; l i t h i u m , s o d i u m a n d p o t a s s i u m a p p a r e n t l y d o n o t form o c t a c h l o r o t h o r a t e s , a difference from r u b i d i u m a n d caesium which w a s d e t e c t e d b y m e a s u r e m e n t of t h e
334 κ . w. BAGNALL
h e a t s of solution of t h e p r o d u c t s of these reactions (Chauvenet, 1911).
These reactions are clearly w o r t h further investigation, for t h e s y s t e m s h a v e n o t b e e n s t u d i e d since first r e p o r t e d , b u t t h e anionic species ThClg-, ThClg^" a n d ThCl7^~ are said t o be formed in fused m i x t u r e s of t h o r i u m t e t r a c h l o r i d e w i t h sodium, p o t a s s i u m , caesium a n d cerium ( I I I ) chlorides ( l o n o v et al., 1960), b u t formation of t h e h e p t a c h l o r o t h o r a t e ( I V ) w a s n o t confirmed b y l a t e r w o r k on t h e p o t a s s i u m chloride t h o r i u m t e t r a c h l o r i d e s y s t e m (Desyatnik et al., 1966). T h e p e n t a -chlorouranate(IV) ion is said t o b e p r e s e n t in u r a n i u m t e t r a c h l o r i d e fused w i t h a m i x t u r e of p o t a s s i u m a n d cuprous chlorides a t 180°
(Taube, 1962).
A l t h o u g h p l u t o n i u m t e t r a c h l o r i d e is u n k n o w n , h e x a c h l o r o p l u t o -n a t e s ( I V ) are readily o b t a i -n e d from a q u e o u s solutio-n (Table X I , p . 333);
t h e r u b i d i u m salt is formed w h e n a m i x t u r e of r u b i d i u m chloride a n d p l u t o n i u m dioxide is h e a t e d in c a r b o n t e t r a c h l o r i d e a t 750° ( F o m i n et al., 1958a), a n d t h e sodium, p o t a s s i u m , r u b i d i u m a n d caesium salts are formed w h e n a m i x t u r e of t h e alkali chloride a n d p l u t o n i u m t r i chloride is h e a t e d in chlorine, a t a b o u t 50° a b o v e t h e melting p o i n t of t h e alkali chloride (Benz a n d Douglass, 1961a), indicating t h a t t h e t e t r a chloride is formed u n d e r t h e s e conditions. O x i d a t i o n t o p l u t o n i u m ( I V ) does n o t occur w i t h m i x t u r e s of p l u t o n i u m trichloride w i t h lithium, calcium or b a r i u m chloride, a n d t h e stabilities of t h e alkali m e t a l salts (and t h e a m o u n t s formed) increase w i t h increasing a t o m i c n u m b e r of t h e alkali m e t a l .
Magnetic susceptibility d a t a h a v e been recorded for CsgUCle a n d (NMe4)2UCl6 ( t e m p e r a t u r e i n d e p e n d e n t p a r a m a g n e t i c ) a n d for (NMe4)2PuCl6 ( t e m p e r a t u r e d e p e n d e n t ) (Candela et al., 1959) a n d crystallographic d a t a a r e available for Cs2ThCl6,Cs2UCl6 (Siegel, 1956), (NMe4)2Th (and Np)Cl6, (NEt4)2Th (and Np)Cl6 (Brown, 1966), CsgPuCle (Zachariasen, 1948b) a n d in m a n y of t h e m o d e r n references given in T a b l e X I (p. 333). T h e a b s o r p t i o n spectra of t h e U X e ^ - ( X = Cl,Br,I), N p X g ^ - a n d P u X g ^ - ions ( X = Cl,Br) h a v e been investigated, t h e optical electronegativities being 1-5 for U ( I V ) , 1-75 for N p ( I V ) a n d 2-05 for P u ( I V ) ( R y a n a n d J o r g e n s e n , 1963).
P y r i d i n i u m h e x a b r o m o t h o r a t e ( I V ) , (pyH)2ThBr6, is r e p o r t e d t o be o b t a i n e d a n h y d r o u s from alcoholic h y d r o b r o m i c acid solutions of t h e t e t r a b r o m i d e a n d p y r i d i n i u m b r o m i d e (Rosenheim a n d Schilling, 1900;
R o s e n h e i m et al., 1903), b u t t h e r e is less risk of hydrolysis if n o n a q u e o u s solvents are used, as in t h e p r e p a r a t i o n of t e t r a e t h y l - a n d t e t r a m e t h y l a m m o n i u m h e x a b r o m o t h o r a t e s ( I V ) a n d h e x a b r o m o u r a -nates(IV) from m e t h y l cyanide solutions of t h e t e t r a b r o m i d e s a n d t h e t e t r a - a l k y l a m m o n i u m b r o m i d e , t h e halo complexes crystallizing w h e n
T H E H A L O G E N C H E M I S T R Y O F T H E A C T I N I D E S 335
the mixture is cooled in ice (Brown, 1966). The hexabromoprotac-tinates(IV) have been made in the same w a y (Brown and Jones, 1967b).
The dark green sodium and potassium hexabromouranates(IV) have been made b y heating the alkali bromide in uranium tetrabromide vapour, a procedure which appears to be less successful with the alkaline earth bromides (Aloy, 1901b) and the triphenylphosphonium salt crystallizes from aqueous acetone-hydrobromic acid (Jorgensen, 1963).
Tetraethylammonium hexabromouranate(IV) has been made from ethanolic hydrobromic acid, from which the salt is precipitated with acetone (Ryan and Jorgensen, 1963), a procedure successfully used b y these authors for the preparation of the corresponding bright yellow neptunium and deep red plutonium compounds; tetramethylammonium hexabromouranate(IV) has also been isolated from 6N hydrobromic acid (Satten et al., 1965), a study being made of the energy levels of the
ion in an octahedral field. The T h — B r and U — B r vibrations appear at 177-179 cm"^ and 178-181 cm-^ respectively in the infrared spectra of the tetraalkylammonium hexabromometallates(IV) ; crystallo
graphic data are also available for some of these salts (Brown, 1966).
Jorgensen (1963) has investigated the spectra of mixed chloride-bromide complex anions in nitromethane solution, obtaining the con
secutive formation constants for the species UBrClg^" and UBr2Cl4^~, the values of which demonstrate once again the typically A character of uranium(IV). The optical absorption spectra of octahedrally coordi
nated in triphenylphosphonium hexachloro- and hexabromo-uranate(IV) have also been reported (Pappalardo and Jorgensen, 1964). Triphenylbutylphosphonium tetrachlorodibromouranate(IV), (Ph3BuP)2UCl4Br2, prepared from the phosphonium bromide and uranium tetrachloride in methyl cyanide solution, has the trans octa
hedral configuration (Day and Venanzi, 1966a).
Although the spectrum of the hexaiodouranate(IV) ion in methyl cyanide has been recorded (Ryan and Jorgensen, 1963), solid hexaiodo-metallates(IV) have only recently been obtained. The yellow thorium and red uranium salts, AgM^^Ig (A = BU4N+, Ph4As+) are made b y reaction of the tetraiodides with the appropriate cation iodide in methyl cyanide solution, the tetraphenylarsonium salts being the more stable (Bagnall et al., 1965a). The blue protactinium(IV) salt, (Ph3MeAs)2Pal6, has been prepared in a similar manner (Brown and Jones, 1967b).
H. Oxyhalides
The only recorded oxyfluoride is the thorium compound, ThOF2, made b y heating together the stoicheiometric quantities of the dioxide and tetrafluoride at 900° in an inert atmosphere (D'Eye, 1958; Darnall,
336 κ. w. BAGNALL
1960), t h e reaction being reversed a t higher t e m p e r a t u r e s ; t h e u r a n i u m c o m p o u n d c a n n o t be o b t a i n e d in t h i s w a y (Spedding a n d Wilhelm, 1944). T h e t h o r i u m c o m p o u n d h a s also b e e n m a d e b y h e a t i n g t h e t e t r a fluoride h y d r a t e t o red h e a t (Chauvenet, 1911) a n d t h e s t r u c t u r e of a specimen o b t a i n e d b y hydrolysis (when t h e tetrafluoride w a s h e a t e d in air) h a s been r e c o r d e d (Zachariasen, 1949a).
T h o r i u m oxychloride is m a d e from t h e dioxide a n d t e t r a c h l o r i d e a t 840° (Smirnov a n d I v a n o v s k i i , 1956; Y e n K u n g - F a n et al, 1963) or b y h e a t i n g t h o r i u m t e t r a c h l o r i d e o c t a h y d r a t e a b o v e 250° in h y d r o g e n chloride (Chauvenet, 1911). A n a d d u c t w i t h m e t h y l cyanide, ThOCl2.2L, is r e p o r t e d t o b e formed b y hydrolysis of t h e t h o r i u m t e t r a c h l o r i d e a d d u c t w i t h t h e stoicheiometric q u a n t i t y of w a t e r (Feltz, 1966). T h e yellow-green u r a n i u m c o m p o u n d h a s been m a d e b y dissolving t h e dioxide in a n excess of t h e m o l t e n t e t r a c h l o r i d e a t 600°, t h e excess of t h e last being r e m o v e d in a v a c u u m a t 450° ( K r a u s , 1942a, 1944). T h i s p r o c e d u r e seems t o give a p u r e r p r o d u c t t h a n t h a t o b t a i n e d b y h e a t i n g u r a n i u m dioxide in t h e v a p o u r of t h e t e t r a c h l o r i d e a t 475° (Davidson a n d Streeter, 1946). T h e u r a n i u m c o m p o u n d is insoluble in a wide r a n g e of organic solvents, b u t is soluble in w a t e r , acids, a n d , w i t h reaction, in m o l t e n p y r i d i n i u m chloride; its a b s o r p t i o n s p e c t r u m h a s been recorded (Ewing, 1961). T h e s t r u c t u r e is p r o b a b l y a n o x y g e n bridged polymer, n o b a n d assignable t o t h e U = 0 v i b r a t i o n being observed in t h e infrared s p e c t r u m (850-1000 cm-^) a n d o x y g e n bridge v i b r a t i o n s a p p e a r i n g a t 735 a n d 720 cm-^ (Selbin a n d Schober, 1966).
T h e yellow n e p t u n i u m oxychloride h a s b e e n m a d e b y v a p o u r p h a s e hydrolysis of t h e t e t r a c h l o r i d e a t 500° (Fried a n d D a v i d s o n , 1948).
T h e oxychlorides of p r o t a c t i n i u m ( I V ) (Brown a n d J o n e s , 1967a), t h o r i u m ( I V ) , u r a n i u m ( I V ) a n d n e p t u n i u m ( I V ) (Bagnall et al, 1967a) are, however, m o r e easily m a d e b y h e a t i n g t h e tetrachlorides w i t h t h e stoicheiometric a m o u n t of a n t i m o n y ( I I I ) oxide. T h e bridging o x y g e n v i b r a t i o n in these p r o d u c t s a p p e a r s a t a b o u t 600 cm-^.
T h o r i u m o x y b r o m i d e , ThOBrg, h a s been m a d e b y h e a t i n g t h e dioxide w i t h s u l p h u r monochloride a n d h y d r o g e n b r o m i d e a t 125° (Bourion, 1907), b y boiling a n a q u e o u s solution of t h o r i u m t e t r a b r o m i d e a n d h e a t i n g t h e residue t o 160° (Moissan a n d M a r t i n s e n , 1905) a n d b y h e a t ing h y d r a t e d t h o r i u m t e t r a b r o m i d e (Chauvenet, 1911). T h e u r a n i u m c o m p o u n d , a greenish-yellow t o yellow solid, h a s been p r e p a r e d b y t h e action of b r o m i n e on t h e oxide-sulphide, U O 2. 2 U S 2 , a t 600° (Spedding et al, 1958). I t is also formed b y t h e decomposition of UOBrg a t r o o m t e m p e r a t u r e ( S h c h u k a r e v et al, 1958a) or, m o r e r a p i d l y , a t 300°. I t s infrared s p e c t r u m shows b a n d s a t 500 a n d 546 cm~^ w h i c h h a v e b e e n assigned t o U — Ο v i b r a t i o n s (Prigent, 1960). I t is also formed, b u t n o t in
T H E H A L O G E N C H E M I S T R Y O F T H E A C T I N I D E S 337
a p u r e s t a t e , b y h e a t i n g u r a n i u m dioxide w i t h t h e t e t r a b r o m i d e (Gregory, 1958). As w i t h t h e oxychlorides, t h e best w a y of p r e p a r i n g t h e o x y b r o m i d e s of p r o t a c t i n i u m ( I V ) (Brown a n d J o n e s , 1967a), t h o r i u m ( I V ) a n d u r a n i u m ( I V ) (Bagnall et al., 1967a) is b y h e a t i n g t h e t e t r a b r o m i d e s w i t h a n t i m o n y ( I I I ) oxide a t 150°. T h e y all dispropor
t i o n a t e a b o v e 500° in a v a c u u m a n d , like t h e u r a n i u m c o m p o u n d , t h e M — Ο v i b r a t i o n s a p p e a r a t a b o u t 500 cm-^, indicating t h a t t h e com
p o u n d s are o x y g e n bridged polymers. B o t h u r a n i u m ( I V ) oxychloride a n d t h e o x y b r o m i d e can b e r e d u c e d t o t h e corresponding t e r v a l e n t oxyhalides (Gregory, 1958).
N e p t u n i u m ( I V ) o x y b r o m i d e is s t a t e d (Zachariasen, 1949b) t o be iso-s t r u c t u r a l w i t h t h e u r a n i u m c o m p o u n d , b u t n o p r e p a r a t i v e detailiso-s h a v e been recorded; X - r a y p o w d e r d a t a , w h i c h h a v e n o t b e e n inter
p r e t e d , are available for u r a n i u m ( I V ) oxychloride a n d o x y b r o m i d e (Zachariasen, 1949b).
T h o r i u m oxyiodide is o b t a i n e d b y h e a t i n g t o g e t h e r t h e dioxide a n d t e t r a i o d i d e a t 600°; its s t r u c t u r e is p r o b a b l y a n infinite chain of t h o r i u m a t o m s linked b y o x y g e n bridges; T h — 0 b a n d s h a v e n o t b e e n observed in t h e infrared s p e c t r u m b e t w e e n 4000 cm~^ a n d 650 cm~^
(Scaife et al., 1965). P r o t a c t i n i u m ( I V ) oxyiodide, a p i n k solid, is formed t o some e x t e n t w h e n t h e t e t r a i o d i d e r e a c t s w i t h silica a b o v e 500°
(Brown a n d J o n e s , 1967a).
4. The Pentavalent Actinides A. General chemistry
Simple p e n t a h a l i d e s a n d oxyhalides h a v e been isolated only for p r o -t a c -t i n i u m ( V ) a n d u r a n i u m ( V ) a n d , in -t h e case of n e p -t u n i u m ( V ) , -t h e h y d r a t e d oxytrifluoride is k n o w n . H o w e v e r , fluoro complexes of all t h e elements from p r o t a c t i n i u m ( V ) t o p l u t o n i u m ( V ) h a v e been p r e p a r e d a n d a few o x y h a l o complexes of t h e s e elements, a n d of americium(V), h a v e been recorded. T h e actinide p e n t a h a l i d e s , like t h e i r (Z-transition element analogues, a r e v e r y sensitive t o m o i s t u r e a n d t h e u r a n i u m ( V ) c o m p o u n d s d i s p r o p o r t i o n a t e i m m e d i a t e l y on exposure t o m o i s t air, or in w a t e r a n d o x y g e n a t e d solvents, b u t are m o r e stable in d r y halo-g e n a t e d h y d r o c a r b o n s , such as chloroform, b r o m o f o r m or c a r b o n t e t r a chloride, a n d in solvents w i t h donor properties, such as t h i o n y l chloride, w i t h which b o t h p r o t a c t i n i u m a n d u r a n i u m p e n t a c h l o r i d e s form stable complexes; t h e r e is also some evidence for t h e existence of a n e p t u n i u m p e n t a c h l o r i d e complex in t h i o n y l chloride. Some crystallographic d a t a are given in T a b l e X I I .
338 κ. w. BAGNALL
C o l o u r S y m m e t r y a n d s p a c e g r o u p
L a t t i c e p a r a m e t e r s ( A )
«0 ^0 Co
C a l c u l a t e d d e n s i t y ( g c m- 3 )
W h i t e T e t r a g o n a l , Ti2d 1 1 - 5 3 5-19 6-28
B l a c k C u b i c , / 4 3 m ( ? ) 8-507 — — 6-83d
(or •Pa,F,)o
P a ^ O F . e W h i t e C u b i c 8 - 4 0 6 5 — — —
a - U F g W h i t e t o T e t r a g o n a l , / 4 / m 6 - 5 2 5 — 4 - 4 7 2 5-81 p a l e b l u e
β-VF, p a l e b l u e W h i t e t o T e t r a g o n a l , U2d 1 1 - 4 7 3
—
5 - 2 0 9 6 - 4 5U^F^ B l a c k C u b i c , / 4 3 m 8-471 — — 7-06
B l a c k D i s t o r t e d U F 4 — — — —
U C I5 R e d - b r o w n M o n o c l i n i c — — — — P a C l ^ e Y e l l o w M o n o c l i n i c , C 2 / c 7-97 1 1 - 3 5 8-36 3 - 7 4
i 3 = 1 0 6 - 4 °
^ V a l u e s f r o m t h e c o r r e c t e d d a t a c o l l e c t e d b y K a t z a n d S h e f t ( 1 9 6 0 ) u n l e s s o t h e r w i s e s t a t e d .
t> S t e i n ( 1 9 6 4 ) . c g t e i n ( 1 9 6 5 ) . d C a l c u l a t e d a s P a g F » ( A u t h o r ) , e D o d g e et al. ( 1 9 6 7 ) .
B. Pentafluorides
Protactinium pentafluoride, a white, crystaUine sohd isomorphous
with J S - U F Q , is made b y heating the tetrafluoride with fluorine at 700°;
it is less volatile than vanadium, niobium and tantalum pentafluorides, subliming in a vacuum above 500° (Stein, 1964). The colourless di
hydrate is obtained b y evaporating a solution of protactinium(V) in concentrated hydrofluoric acid to dryness (Grosse, 1934a; Stein, 1964).
It decomposes to the oxyfluoride, PagOFg, at 160° (Stein, 1964). The infrared spectra of the protactinium(IV) fluorides and ( V ) oxyfluorides have been recorded, the P a — F vibration appearing at 400 cm-^ in PaF^ and Pa^F^^ and at 450 cm-^ in PaaOFg (Stein, 1965); the Pa—Ο vibrations in the last appear at 790, 740 and 690 cm~^.
Uranium pentafluoride, first obtained b y Grosse (1958c) b y reaction of uranium tetrafluoride with the hexafluoride at 95-100°, exists in two crystalline forms, both of tetragonal symmetry. The high-temperature α-form is made b y the action of fluorine on uranium tetrafluoride a t 150° (Agron et al., 1958) or b y reaction of the tetrafluoride with uranium hexafluoride at 230-250° (Wolfed al., 1965a), a reaction which yields t h e
β-ΘοτίΆ below 125°. jS-Uranium pentafluoride is obtained b y the action of hydrogen fluoride on uranium pentachloride (Agron et aL, 1958), a reaction previously investigated b y Ruff and Heinzelmann (1911), and is precipitated on addition of boron trifluoride to a solution of nitrosonium
TABLE X I I . S o m e c r y s t a l l o g r a p h i c d a t a for t h e a c t i n i d e p e n t a h a l i d e s *
T H E H A L O G E N C H E M I S T R Y O F T H E A C T I N I D E S 339
hexafluorouranate(V) in a n h y d r o u s hydrofluoric acid (Geichman et aL, 1962a). T h e α-form is b e s t m a d e b y r e a c t i o n of h y d r o g e n b r o m i d e w i t h u r a n i u m hexafluoride a t 65° (Wolf aL, 1965b), a r e a c t i o n w h i c h can also be m a d e t o yield t h e j8-form b y s u i t a b l e t e m p e r a t u r e c o n t r o l ( H o b b s , 1962). B o t h forms are w h i t e t o c h a l k y b l u e in a p p e a r a n c e ; d i s p r o p o r t i o n a t i o n occurs slowly a b o v e 150° (Priest, 1958). H o w e v e r , a-UFg m e l t s a t 348°; v a p o u r pressure d a t a are available for b o t h t h e solid a n d liquid (Wolf et aL, 1965a), a n d m a g n e t i c susceptibility d a t a for jS-UFg h a v e b e e n recorded ( N g u y e n - N g h i et aL, 1964).
O t h e r actinide pentafluorides are u n k n o w n , a l t h o u g h a n a b n o r m a l increase in t h e v a p o u r pressure of p l u t o n i u m tetrafluoride a t 900° in a v a c u u m h a s been t e n t a t i v e l y ascribed t o d i s p r o p o r t i o n a t i o n t o p l u t o n i u m t r i - a n d pentafluorides; however, t h e volatile p r o d u c t , w h i c h h a s n e v e r b e e n characterized, was s t a b l e in air, so t h a t it is unlikely t o h a v e been a pentafluoride (Dawson et aL, 1954b).
A p a r t from P a F 5 . 2 H 2 0 , m e n t i o n e d a b o v e , complexes of t h e p e n t a fluorides w i t h o x y g e n a n d n i t r o g e n d o n o r ligands are u n k n o w n .