T h e only c o m p o u n d recorded is t h e b u t o x y d e r i v a t i v e , UCl2Br(OBu)2, o b t a i n e d b y t r e a t i n g UCl2(OBu)2 w i t h b r o m i n e in t e t r a h y d r o f u r a n ; it r e a c t s w i t h sodium c y c l o p e n t a d i e n i d e in t e t r a h y d r o f u r a n t o form t h e b u t o x y t r i s c y c l o p e n t a d i e n i d e , U(C5H5)3(OBu)2 ( E t h y l Corporation, 1963, R e p o r t T I D - 1 9 3 6 7 ) .
H. Halo complexes
P r o t a c t i n i u m ( V ) is v e r y stable t o hydrolysis in a q u e o u s hydrofiuoric acid, in c o n t r a s t t o its b e h a v i o u r in t h e o t h e r halogen acids, a n d u r a n -ium(V) is likewise stable in c o n c e n t r a t e d (or a n h y d r o u s ) hydrofiuoric acid, one of t h e few solvents in w h i c h it does n o t d i s p r o p o r t i o n a t e . E v a p o r a t i o n of t h e p r o t a c t i n i u m solution yields t h e pentafluoride di-h y d r a t e , as a l r e a d y m e n t i o n e d , w di-h e r e a s cooling t di-h e b l u e u r a n i u m ( V ) solution in c o n c e n t r a t e d hydrofluoric acid t o —10° yields blue crystals of t h e hexafluorouranic(V) acid, HUF6,2-5H20 (Asprey a n d P e n n e m a n ,
1964a).
F l u o r o complexes of t h e t y p e s A^MFg, A2MF7 a n d AgMFg are n o w k n o w n for b o t h p r o t a c t i n i u m , u r a n i u m a n d n e p t u n i u m , b u t only t h e hexa- a n d heptafluoro complexes of p l u t o n i u m h a v e b e e n m a d e so
344 κ. w. B A G N A L L
far. A m m o n i u m , p o t a s s i u m a n d r u b i d i u m hexailuoroprotactinates(V) (Asprey a n d P e n n e m a n , 1964b) h a v e been o b t a i n e d b y e v a p o r a t i n g equimolar q u a n t i t i e s of p r o t a c t i n i u m ( V ) a n d t h e alkali fluoride in h y d r o fluoric acid t o dryness. H o w e v e r , t h e salts m a d e in t h i s w a y always contain some heptafluoroprotactinate(V) a n d it is advisable t o e v a p o r a t e t o small volume, discarding t h e first crop of crystals (the heptafluoro complex) a n d t h e n t o a d d a further q u a n t i t y of 20M hydrofluoric acid, finally e v a p o r a t i n g t h e solution u n t i l crystallization occurs (Keller a n d C h e t h a m - S t r o d e , 1965). A b e t t e r m e t h o d of p r e p a r i n g these salts is b y fluorine oxidation of equimolar q u a n t i t i e s of p r o t a c t i n i u m tetrafluoride a n d t h e alkali m e t a l fluoride (Asprey et aL, 1965b,c). T h e p r o t a c t i n i u m c o m p o u n d s (Brown a n d E a s e y , 1966) are isostructural w i t h t h e u r a n i u m ( V ) analogues, possessing o r t h o r h o m b i c s y m m e t r y (Charpin, 1965).
P o t a s s i u m heptafluoroprotactinate(V), K2PaF7, first p r e p a r e d b y Grosse (1934b, 1935) b y t r e a t i n g t h e h y d r a t e d pentafluoride w i t h a q u e o u s p o t a s s i u m fluoride, is r e m a r k a b l y stable t o hydrolysis a n d can b e recrystallized from w a t e r ; t h e caesium salt, however, c a n n o t be o b t a i n e d from a q u e o u s solution b y e v a p o r a t i o n because of its suscepti
bility t o hydrolysis a n d is v e r y soluble in w a t e r or a q u e o u s hydrofluoric acid. H o w e v e r , this, a n d t h e a m m o n i u m , p o t a s s i u m a n d r u b i d i u m salts, are easily o b t a i n e d b y p r e c i p i t a t i n g t h e m from 17M hydrofluoric acid solution w i t h a large v o l u m e of acetone (Brown a n d E a s e y , 1966), a procedure which is unsuccessful in t h e case of t h e smaller l i t h i u m cation a n d which yields only t h e octafluoroprotactinate(V), NagPaFg, in t h e case of sodium (Brown a n d E a s e y , 1965, 1966), t h e last being also o b t a i n e d even w h e n a hydrofluoric acid solution containing 2 moles of sodium fluoride per mole of p r o t a c t i n i u m ( V ) is e v a p o r a t e d t o dryness.
T h e preferential crystallization of NagPaFg h a s also been n o t e d b y B u k h s h et aL (1966). P o t a s s i u m , r u b i d i u m a n d caesium octafluoro-p r o t a c t i n a t e s ( V ) , which c a n n o t b e octafluoro-p r e octafluoro-p a r e d from hydrofluoric acid solution, are m a d e b y h e a t i n g t o g e t h e r t h e stoicheiometric q u a n t i t i e s of t h e heptafluoro complex salt a n d t h e a p p r o p r i a t e alkali fluoride a t 450° in d r y a r g o n or e v e n in air, a n d t h e l i t h i u m salt h a s been m a d e b y e v a p o r a t i n g t o dryness t h e stoicheiometric q u a n t i t i e s of lithium fluoride a n d p r o t a c t i n i u m ( V ) in hydrofluoric acid solution a n d d e h y d r a t i n g t h e p r o d u c t a t 450° in air (Brown a n d E a s e y , 1966). T h e P a —F v i b r a t i o n s in t h e infrared s p e c t r u m a p p e a r a t 523, 454 cm-^ in K P a F g , 430, 356 cm-^ in K2PaF7 a n d a t 401 cm~^ in KgPaFg, increasing coordination leading t o a n increase in t h e w a v e l e n g t h of t h e P a —F stretching vibra
tion as would be e x p e c t e d (Brown a n d E a s e y , 1966); some crystallo
graphic d a t a h a v e been r e p o r t e d for these c o m p o u n d s b y t h e a u t h o r 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 345
q u o t e d a b o v e , as well as a full s t r u c t u r e analysis of KgPaFy (Brown a n d S m i t h 1965; B r o w n et al, 1967), a n d t h e R a m a n s p e c t r a of R b P a F g a n d Rb2PaF7 h a v e b e e n recorded (Keller a n d C h e t h a m - S t r o d e , 1965).
T h e corresponding u r a n i u m ( V ) fluoro complexes h a v e also b e e n investigated in some detail; greenish-white n i t r o s o n i u m hexafluoroura-nate(V), NOUFg, which is of pseudo-cubic s y m m e t r y , h a s b e e n p r e p a r e d b y reaction of nitric oxide w i t h u r a n i u m hexafluoride, a n analogous reaction occurring w i t h m o l y b d e n u m hexafluoride, b u t n o t w i t h t u n g s t e n hexafluoride, which r e m a i n s u n c h a n g e d ; n o reaction occurs w i t h n i t r o u s oxide (Ogle et al, 1959; G e i c h m a n et al, 1962c). T h e n i t r o sonium salt is also m a d e b y t h e r e a c t i o n of u r a n i u m hexafluoride w i t h nitrosyl chloride (Geichman et al, 1963), a r e a c t i o n w h i c h leads t o t h e analogous p r o d u c t w i t h m o l y b d e n u m hexafluoride, a n d b y reaction of t h e pentafluoride w i t h nitrosyl fluoride (Geichman et al, 1962c). T h e n i t r o s o n i u m salt is decomposed b y acetone, m e t h a n o l a n d trichloro-e t h y l trichloro-e n trichloro-e a n d is insolubltrichloro-e in carbon t trichloro-e t r a c h l o r i d trichloro-e , F r trichloro-e o n - 1 1 3 , chloro
benzene a n d n i t r o g e n dioxide (Ogle et al, 1959). N i t r o s o n i u m h e x a -fluorouranate(V) r e a c t s w i t h fluorine, chlorine trifluoride or v a n a d i u m pentafluoride in a n h y d r o u s hydrofluoric acid, u r a n i u m hexafluoride being evolved; t h e solid is reduced t o u r a n i u m tetrafluoride b y h y d r o g e n a t 300-350° or b y carbon m o n o x i d e a t 300° (Geichman et al, 1962a).
T h e n i t r o n i u m c o m p o u n d is likewise o b t a i n e d b y t h e action of n i t r o g e n dioxide on u r a n i u m hexafluoride (Geichman et al, 1962b). T h e kinetics of hydrolysis of t h e n i t r o s o n i u m salt over t h e r a n g e 68-231° h a v e also been s t u d i e d (Massoth et al, 1960).
T h e w h i t e a m m o n i u m salt, NH4UF6, w a s originally m a d e b y r e a c t i o n of a n excess of u r a n i u m hexafluoride w i t h a m m o n i a ( R a m p y , 1959b), a l t h o u g h it h a s been r e p o r t e d t h a t t h e p r o d u c t of t h i s reaction a t 25° is a m i x t u r e of u r a n i u m pentafluoride a n d a m m o n i u m pentafluoroura-n a t e ( I V ) (Galkipentafluoroura-n et al, 1960). H o w e v e r , R a m p y (1959b) foupentafluoroura-nd t h a t t h e p r o d u c t of t h e r e a c t i o n w a s soluble in 4 8 % hydrofluoric acid, forming a blue solution from which pale green KUFg was p r e c i p i t a t e d on a d d i t i o n of p o t a s s i u m fluoride; he also o b t a i n e d some indications of t h e formation of K2UF7. T h e a m m o n i u m salt is b e s t p r e p a r e d b y h e a t i n g u r a n i u m pentafluoride w i t h a m m o n i u m fluoride in a sealed t u b e a t 80-85°
( P e n n e m a n et al, 1962), or b y prolonged h e a t i n g of t h e hexafluoride w i t h a m m o n i u m fluoride a t 120°. I t decomposes, w i t h t h e evolution of fluorine, a t 150° in a v a c u u m or in argon (Nguyen-Nghi et al, 1965a,b).
G e i c h m a n et al (1962a) t h e n o b t a i n e d l i t h i u m , sodium, silver a n d calcium hexafluorouranates(V) b y h e a t i n g t h e n i t r o s o n i u m salt w i t h t h e a p p r o p r i a t e n i t r a t e s until no further evolution of dinitrogen t e t r a o x i d e occurred. T h e w h i t e calcium c o m p o u n d w a s also m a d e b y h e a t i n g a
346 κ . w . BAGNALL
mixture of uranium tetrafluoride and calcium fluoride in fluorine at 210° and the sodium, potassium and silver salts were obtained from 4 8 % (Na,K) or anhydrous (K,Ag) hydrofluoric acid. The alkaH metal salts are best prepared from solutions of the pentafluoride in concen
trated aqueous (10-27M) hydrofluoric acid and the appropriate alkali fluoride (Asprey and Penneman, 1964a), or b y treating a mixture of the pentafluoride and alkali fluoride with anhydrous hydrofluoric acid (Sturgeon et al., 1965), a procedure successfully used for the preparation of the blue sodium salt, which is dimorphic, and the pale yellow-green ammonium, potassium, rubidium and caesium salts, for which X-ray crystallographic data are available. Analysis of the optical absorption spectrum of CsUFg shows that the U F g - ion has a shghtly distorted octahedral configuration (Reisfeld and Crosby, 1965).
The magenta caesium hexa- and rubidium heptafiuoroneptunates(V) (Asprey et al., 1966), the analogous green fluoroplutonates(V) (Penne
man et al., 1965), and rubidium octafluoroneptunate(V) (Bagnall et al., 1967b) have been made b y heating the appropriate quadrivalent actinide fluoride compounds in fluorine at 250-300° (Np) or 300-400°
(Pu). Caesium hexafluoroneptunate(V) can also be prepared b y the action of fluorine on a 1:1 mixture of caesium fluoride and neptunium tetrafluoride in anhydrous hydrofluoric acid (Asprey and Penneman,
1967).
The lithium, sodium, potassium, rubidium and caesium hexafluo-rouranates(V) can also be made b y heating together the stoicheiometric quantities of uranium pentafluoride and the alkali fluoride at 300°;
when a 2:1 mixture of alkali fluoride and uranium pentafluoride is treated in this way, all, except lithium, which forms only LiUFg, yield a mixture of the hexa- and octafluoro complexes. Apart from the sodium salts, these, when heated at 350°, react to give the heptafluo-rouranates(V), identified as new phases b y X-ray powder photography;
they are not isostructural with the heptafluoroprotactinates(V). The octafluorouranates(V) of all except lithium are prepared in a similar manner, using the appropriate quantity of alkali fluoride. The corre
sponding ammonium salts are made in the same way, but at a lower temperature; these salts and the alkali metal compounds are almost white (Penneman et al., 1964b).
Sodium octafluorouranate(V) has also been made b y heating sodium heptafluorouranate(IV) in fluorine at 390° and its magnetic behaviour has been recorded, together with X-ray crystallographic data (Riidorfif and Leutner, 1960). B o t h silver hexafluorouranate(V) and the octa
fluorocomplex have been made from j8-uranium pentafluoride and silver fluoride at 350-400°; crystallographic data for these compounds, and
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 347
t h e i r infrared spectra, h a v e been recorded (Bougon a n d Plurien, 1965).
L i t h i u m a n d silver hexafluorouranates(V) a r e said t o decompose w i t h t h e evolution of fluorine, a t 400° a n d 230° respectively (Nguyen-Nghi et al, 1965b).
T h e pale-yellow caesium, t e t r a m e t h y l a m m o n i u m a n d t e t r a p h e n y l a r s o n i u m h e x a c h l o r o p r o t a c t i n a t e s ( V ) (Bagnall a n d B r o w n , 1964) a n d t h e corresponding deep-yellow t o orange h e x a c h l o r o u r a n a t e s ( V ) , a n d t h e d i m e t h y l a m m o n i u m salt of t h e l a t t e r (Bagnall et al, 1964c) h a v e been p r e p a r e d from solutions of t h e c o m p o n e n t s in t h i o n y l chloride ( a l k y l a m m o n i u m a n d a r y l a r s o n i u m salts) or in a m i x t u r e of iodine monochloride a n d t h i o n y l chloride (caesium salts). B r i g h t yellow t e t r a m e t h y l a m m o n i u m octachloroprotactinate(V) a n d t h e pale yellow o c t a -chlorouranate(V) h a v e also been isolated from t h i o n y l chloride solution.
T h e infrared s p e c t r a of these c o m p o u n d s h a v e b e e n recorded; t h e Pa—CI v i b r a t i o n a p p e a r s a t 308 cm-^ in NMe4PaCl6 a n d a t 290 cm"^ i n (NMe4)3PaCl8, consistent w i t h t h e increased coordination n u m b e r of t h e m e t a l ion, a n d a t 310 cm-^ in b o t h h e x a - a n d o c t a c h l o r o u r a n a t e s ( V ) , p r o b a b l y because of decomposition of t h e l a t t e r in t h e Nujol mull. T h e m a g n e t i c properties of t h e u r a n i u m ( V ) chloro complexes h a v e also b e e n recorded. Conductio-metric t i t r a t i o n of u r a n i u m pentachloride (UCI5.
SOCI2) a g a i n s t p y r i d i n e in t h i o n y l chloride h a s given some evidence for t h e existence of t h e h e p t a c h l o r o u r a n a t e ( V ) ion, b u t n o salts of t h i s i o n h a v e been isolated (Bagnall et al, 1964c). X - r a y diffraction d a t a for some of t h e hexachloro c o m p o u n d s are available (Bagnall a n d B r o w n , 1964).
A l t h o u g h analogous n e p t u n i u m ( V ) c o m p o u n d s h a v e n o t b e e n isolated, t e t r a p h e n y l a r s o n i u m o x y p e n t a c h l o r o n e p t u n a t e ( V ) , (Ph4As)2NpOCl5, dissolves in t h i o n y l chloride t o give a d a r k - r e d solution which p r o b a b l y contains t h e h e x a c h l o r o n e p t u n a t e ( V ) anion; t h e a b s o r p t i o n s p e c t r u m of t h e solution h a s been recorded, b u t t h e n e p t u n i u m species d e c o m poses r a p i d l y ; on a d d i t i o n of c a r b o n disulphide a m i x t u r e of t h e h e x a -c h l o r o n e p t u n a t e ( I V ) a n d a n unidentified n e p t u n i u m ( V ) -chloro -complex precipitates from t h e solution (Bagnall a n d Laidler, 1966).
T h e orange t e t r a e t h y l a m m o n i u m h e x a b r o m o p r o t a c t i n a t e ( V), N E t 4 P a B r 6 (Brown, 1965) a n d t h e b r o w n t r i p h e n y l m e t h y l a r s o n i u m h e x a i o d o p r o t a c t i n a t e ( V ) h a v e been p r e p a r e d from a m e t h y l c y a n i d e solution of t h e c o m p o n e n t s (Brown et al, 1967).
I. Oxyhalides
P r o t a c t i n i u m oxyfiuoride, PagOFg, a w h i t e , hygroscopic solid iso-s t r u c t u r a l w i t h U2F9 (body-centred cubic), iiso-s iso-slightly volatile in v a c u u m a b o v e 500° ; it is m a d e b y t h e r m a l decomposition of t h e pentafluoride
348 κ. w. B A G N A L L
dihydrate at 160° and b y reaction of the pentoxide with fluorine at 550°
or with an equimolar mixture of hydrogen fluoride and o x y g e n at 500°.
I t decomposes above 800°, yielding the pentafluoride among other, unidentified, products (Stein, 1964). The uranium analogue, UgOFg, a white solid, is obtained b y heating uranium tetrafluoride at 850° in an intermittent oxygen flow; it is unstable in air and is very hygroscopic.
I t decomposes in a vacuum at 300° (Kirslis et al., 1950):
2U2OF8 ^ U F e + UO2F2 + 2UF4
The corresponding protactinium oxychloride, PagOClg, is obtained as a by-product of the reaction of a mixture of chlorine and carbon tetra
chloride with protactinium pentoxide mixed with carbon and a second crystal modification of this compound is obtained b y heating the penta
chloride with the stoicheiometric amount of oxygen in a sealed tube at 350-400°. Thermal decomposition of PagOClg at 270° in a vacuum, or treatment of the pentachloride with the appropriate amounts of oxygen at 350-400°, yields the oxychloride P a 2 0 3 C l 4 and there is some evidence for the formation of PaOCla. Thermal decomposition of P a 2 0 3 C l 4 at 520° in a vacuum yields the dioxochloride PaOgCl. All of these com
pounds are oxygen bridged polymers (Brown and Jones, 1966a).
Compounds of the general form MOX3 are also known; UOF3 is thought t o be formed as an intermediate in the reaction between uranium dioxide and hexafluoride at 500°, the final products of which are uranium tetrafiuoride and uranyl fiuoride (Rampy, 1959a). The green hydrated neptunium analogue has been prepared b y the action of hydrogen fluoride on neptunium pentoxide at 40° (Bagnall et al., 1966c).
Reddish-brown UOCI3 is usually prepared b y heating an equimolar mix
ture of uranium tetrachloride and uranyl chloride at 370° (Shchukarev et al., 1958b; M. D . Adams et al., 1963); it is formed as an intermediate in the reaction of uranium dioxide, triuranium octaoxide or uranium(IV) oxychloride with carbon tetrachloride, and in the reaction of uranium dioxide with hexachloropropene; a brown compound of composition U2O3CI3 is also formed in these reactions. Uranium oxytrichloride is insoluble in benzene or carbon tetrachloride, but is soluble, with de
composition, in methanol, ethanol and in water (Budaev and Vol'skii, 1958). I t s heat of formation has been reported as —283-4 (Shchukarev et al., 1958b) and —281-4 kcal mole-^ (Kao-P'in K'uo, 1959), in reason
able agreement. A dark-brown ethanol adduct, UOCl3.EtOH, is obtained b y the action of ethanol on the thionyl chloride complex, UCI5.SOCI2 (Bradley et al., 1957). The oxochloro complex, CSUOCI4, has been made b y reaction of the hexachloro complex, CsUClg, with antimony(III) oxide (Bagnall et al., 1967a).
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 349