M o l y b d e n u m ( V ) fluoride h a s been p r e p a r e d j u s t recently (Peacock, 1957b; K e m m i t t a n d S h a r p , 1961; E d w a r d s et al., 1962b; O'Donnell a n d S t e w a r t , 1962). R e d u c t i o n of t h e hexafluoride w i t h either m o l y b d e n u m or t u n g s t e n h e x a c a r b o n y l or w i t h m o l y b d e n u m m e t a l gives a p u r e p r o d u c t . F l u o r i n e diluted w i t h n i t r o g e n converts m o l y b d e n u m m e t a l t o a p r o d u c t of low p u r i t y , while fluorination of t h e h e x a c a r b o n y l (at —75°) gives MogFg (either (MoF3+)(MoF6-) or a m i x t u r e of M0F4 a n d M0F5), which on h e a t i n g t o 170° gives yellow, volatile M0F5. S u l p h u r tetrafluoride m a y convert m o l y b d e n u m ( I V ) sulphide t o t h e p e n t a fluoride as a n i n t e r m e d i a t e step. T h e reaction b e t w e e n PF3 a n d MoF^
also gives t h e pentafluoride.
M o l y b d e n u m pentachloride, t h e stable p r o d u c t of chlorination of m o l y b d e n u m m e t a l , h a s been k n o w n for a long t i m e . T h e chlorination h a s b e e n carried o u t using flow t e c h n i q u e s ( W a r d l a w a n d W e b b , 1930;
K o r s h u n o v a n d Gol'den, 1961; P e a r s o n a n d Garner, 1961; Colton a n d T o m k i n s , 1965). I t is claimed t h a t t h e p r o d u c t formed in t h i s w a y is of low p u r i t y (Campbell, 1959). Molybdenite ores h a v e b e e n chlorinated a t 400-450°, which is t h e b e s t t e m p e r a t u r e r a n g e (Senderoff a n d L a b r i e , 1955; G l u k h o v a n d B e k h t l e , 1958a). Chlorination of m o l y b d e n u m ( V I ) oxide using chlorine, carbonyl chloride, or t h i o n y l chloride in conjunc
t i o n w i t h sodium or p o t a s s i u m chloride h a s been used (Horizons, 1959).
T h i o n y l chloride (Seifert a n d Q u a k , 1961), a n d c a r b o n t e t r a c h l o r i d e ( S h c h u k a r e v et al., 1956b; K n o x et al., 1957) chlorinate t h e oxide directly, giving good yields, while c a r b o n t e t r a c h l o r i d e will also chlorinate t h e sulphides of m o l y b d e n u m t o give t h e p e n t a c h l o r i d e (Bardaivil et al., 1964).
T h e pentachloride h a s often b e e n described as green, b u t t h i s is d u e t o t h e oxychloride i m p u r i t y M0OCI4 (as m u c h as 5%) which forms a coating over t h e black p e n t a c h l o r i d e (Pearson a n d Garner, 1961;
Colton a n d T o m k i n s , 1965). Purification from t h e oxychloride h a s been achieved b y e x t r a c t i o n of t h e l a t t e r i n t o c a r b o n t e t r a c h l o r i d e in vacuo, or r e m o v a l b y v a c u u m s u b l i m a t i o n a t 80-90°.
T h e p r e p a r a t i o n of t u n g s t e n ( V ) chloride h a s b e e n i n a d e q u a t e l y studied. R e d u c t i o n of t u n g s t e n ( V I ) chloride w i t h h y d r o g e n (Gmelin, 1933; B r e w e r et al., 1950) often gives a p r o d u c t c o n t a m i n a t e d w i t h
266 J . Ε. FERGUSSON
C o m F o r m a t i o n d a t a S° M e l t i n g
p o u n d (e.u.) p o i n t (e.u.)
( k c a l ( k c a l (e.u.) (°C)
mole~^) mole~^)
M 0 F 5 67a 25-4a
M 0 C I 5 126, 9 P 68-5 77, 5 3 c 194d 22
W C I 5 137, 82i> 6 0 71, 15^ 58C 230, 2 4 4 e 23-9^
W B r ^ 60 37 77 286, 276g 2 1 · 8 δ
—
V a l u e s u n d e r l i n e d a r e e s t i m a t e d (cf. B r e w e r et al., 1 9 5 0 ) .
a C a d y a n d H a r g r e a v e s ( 1 9 6 1 b ) . ^ S h c h u k a r e v a n d N o v i k o v ( 1 9 5 6 ) .
^ S h c h u k a r e v et al. ( 1 9 6 0 a ) . f S h c h u k a r e v et al. ( 1 9 5 8 a ) . c L a t i m e r ( 1 9 5 2 ) . g S h c h u k a r e v a n d N o v i k o v (1959) d S h c h u k a r e v et al. ( 1 9 5 9 b ) .
The differing thermal behaviour is outlined in Table X V I I ; again the tungsten compounds appear more stable. The high entropy of vaporiza
tion of the tetrafluoride suggests self-association in t h e liquid state which certainly occurs in t h e solid state (see below). There m a y also be some self-ionization in t h e liquid state t o give M0F4+M0F6- (Cady and
TABLE X V I I . T h e r m a l p r o p e r t i e s o f p e n t a h a l i d e s M 0 F 5 A t 1 6 5 ° g i v e s M 0 F 4 a n d MoF^.^.i?
M 0 C I 5 A t h i g h t e m p e r a t u r e s g i v e s M 0 C I 4 a n d C l g .
W C I 5 W C I 4 a n d W C l f i p r o d u c t s o f d i s s o c i a t i o n i n g a s e o u s state.c»d W B r g A t e l e v a t e d t e m p e r a t u r e s g i v e s W B r 4 a n d B r ^ . ^
a E d w a r d s et al. ( 1 9 6 2 b ) . c S h c h u k a r e v et al. ( 1 9 5 8 a , 1 9 5 9 b ) .
^ C a d y a n d H a r g r e a v e s ( 1 9 6 1 b ) . ^ B r e w e r et al. ( 1 9 5 0 ) .
oxychlorides and the reduction does not go cleanly to t h e pentavalent state. Phosphorus in slightly more than stoichiometric amounts has been used as t h e reducing agent (Novikov et al., 1961).
Of the pentabromides only t h e tungsten compound is known. Molyb-denum(V) bromide m a y be stable at high pressures of bromine (Brewer et al., 1950). The reaction between tungsten metal or tungsten hexa
carbonyl and bromine gives t h e black pentabromide (Emeléus and Gutmann, 1950; Shchukarev and Novikov, 1959). I n t h e latter case WBrg is formed first and decomposes at 250° t o the pentabromide.
Hydrogen bromide reduces tungsten(VI) chloride t o t h e pentavalent bromide.
Table X V I collects together some of t h e data on t h e pentahalides.
The compounds are readily converted t o oxyhalides b y moisture and oxygen (Pearson and Garner, 1961; Edwards et al., 1962b; Colton and Tomkins, 1965).
TABLE X V I . M o l y b d e n u m ( V ) a n d t u n g s t e n ( V ) h a l i d e s
H A L I D E C H E M I S T R Y O F C H R O M I U M , M O L Y B D E N U M A N D T U N G S T E N 267
1/
F F
Γ Mo F Mo ·
i / \ \/l
• Mo F Mo F F
F F FiG. 3 . T h e structure of t h e t e t r a m e r i c M0F5.
H a r g r e a v e s , 1961b; E d w a r d s et at., 1962). W h e r e a s M0CI5 is m o n o m e r i c in t h e gaseous s t a t e t h e r e is evidence t h a t t h e t u n g s t e n c o m p o u n d is p a r t l y dimeric ( 1 0 % ) , while t h e b r o m i d e is m o n o m e r i c ( S h c h u k a r e v et al., 1958a, 1959a; S h c h u k a r e v a n d N o v i k o v , 1959).
M o l y b d e n u m ( V ) chloride undergoes v a r y i n g degrees of solvolysis in solvents such a s m e t h a n o l , e t h a n o l , aliphatic acids, a m m o n i a , a n d pri
m a r y a n d secondary amines ( E d w a r d s a n d Fowles, 1961a,b; W a r d l a w a n d W e b b , 1930; Fowles a n d McGregor, 1958; L a r s o n , 1960, 1962;
F u n k et al., 1961; P a u l a n d M a l h o t r a , 1963). T h e p r o d u c t s a r e generally of t h e t y p e M0CI3X2; e.g., MoCl3(NH2).NH3 a n d MoCl3(NR2)2, still containing p e n t a v a l e n t m o l y b d e n u m . T e r t i a r y amines give 1:1 a n d 1:2 m o l y b d e n u m ( V ) a d d u c t s , while i n p y r i d i n e r e d u c t i o n t o lower o x i d a t i o n s t a t e s occurs. M o l y b d e n u m ( V ) chloride a p p e a r s t o a b s t r a c t o x y g e n from o x y g e n d o n o r ligands t o give M0OCI3, a n d in excess ligand t o give M0O2CI2. H o w e v e r , triphenylarsineoxide does form a simple a d d u c t MoCl5.Ph3AsO {μ - 1-61 Β) (Horner a n d Tyree, 1962), as does POCI3 ( G u t m a n n , 1952). Some of t h e reactions w i t h oxide ligands h a v e been carried o u t in c a r b o n tetrachloride, a n d m a y b e complicated b y t h e fact t h a t t h e p e n t a c h l o r i d e dissociates in this solvent t o give m o l y b -d e n u m ( I V ) chlori-de a n -d chlorine (Pearson a n -d Garner, 1961).
T u n g s t e n ( V ) b r o m i d e also undergoes solvolysis reactions similar t o m o l y b d e n u m ( V ) chloride ( F u n k a n d Schauer, 1960), a n d in a d d i t i o n b o t h t h e chloride a n d b r o m i d e form t h e a p p a r e n t l y seven coordinate c o m p l e x e s W X 5 . 2 p y , W C l 5 ( d i p y r i d y l ) , W B r 5 (o-phen) a n d WBr5(Ph3P)2.
T h e chlorides a r e m a d e from t u n g s t e n ( V I ) chloride a n d t h e b r o m i d e s from t h e p e n t a v a l e n t b r o m i d e i n strict absence of o x y g e n or oxygen-containing solvents ( J . E . Fergusson, u n p u b l i s h e d ) .
A n u m b e r of workers h a v e s t u d i e d t h e m a g n e t i c properties of m o l y b -d e n u m ( V ) chlori-de (Sucksmith, 1932; K l e m m a n -d Steinberg, 1936; K n o x a n d Coffey, 1959; Colton a n d T o m k i n s , 1965). Older w o r k a p p e a r s t o b e in error d u e t o t h e presence of oxychloride impurities i n t h e c o m p o u n d .
2 6 8 J . Ε . F E R G U S S O N
A r e c e n t v a l u e of 1-67 Β {θ close t o zero) is v e r y likely t h e best avail
able (Colton a n d T o m k i n s , 1965), r e d u c e d below t h e spin-only v a l u e d u e t o s p i n - o r b i t coupling. T u n g s t e n ( V ) chloride a n d b r o m i d e also h a v e low m o m e n t s : 1-12 Β a n d 1-07 Β (293°) respectively. I t h a s been sug
gested t h a t t h e m o m e n t s agree w i t h a trimeric formulation [WgXig]^"^
3 Χ - (Colton a n d M a r t i n , 1965). S p i n - o r b i t coupling m a y also b e a reason for t h e low values.
M o l y b d e n u m ( V ) fluoride is t e t r a m e r i c in t h e solid s t a t e (Fig. 3), w i t h t h r e e M o — F distances, 1- 8 5 Â a n d 1-70 Â t o t e r m i n a l fluorine a t o m s , a n d 2-06 Â t o bridging fluorine a t o m s . T h e former b o n d s are r a t h e r short, suggesting some b a c k - b o n d i n g ( E d w a r d s et al., 1962b). I n view of this s t r u c t u r e , spectral a n d m a g n e t i c d a t a would b e of interest.
Gaseous m o l y b d e n u m ( V ) chloride is m o n o m e r i c , w i t h a trigonal bi-p y r a m i d s t r u c t u r e (Mo—CI = 2-27 Â) (Ewens a n d Lister, 1938), whereas in t h e solid s t a t e it is dimeric w i t h o c t a h e d r a l coordination a r o u n d each m e t a l . B o n d lengths are Mo—Clterminai 2-24 Â, Mo—Clbridge = 2-53 Â w i t h a m e t a l - m e t a l distance of 3-83 Â (Sands a n d Zalkin, 1959).
I n solution t h e p e n t a c h l o r i d e is considered t o be m o n o m e r i c w i t h Dg^ s y m m e t r y , which is of interest because t h e single (î-electron will reside in a d o u b l y d e g e n e r a t e g r o u n d s t a t e . (Dissociation in solution m a y be a complicating factor). A J a h n - T e l l e r distortion, observable in t h e electronic a b s o r p t i o n s p e c t r u m , would be expected. A distortion of t h e t y p e Mo—CI (equatorial) = 2 - 1 5 Â a n d Mo—CI (polar) 2-40 A is claimed t o give a reasonable flt b e t w e e n t h e o r y a n d t h e observed spec
t r u m . T h e t w o b a n d s a t 15,200 a n d 21,300 cm~^ are said t o be split d u e t o t h e distortion (Bader a n d W e s t l a n d , 1961).
T h e emission s p e c t r u m of t h e p e n t a c h l o r i d e changes b e t w e e n 200 a n d 300°, p r o b a b l y d u e t o depolymerization (Mesnage, 1939). B o t h spectral a n d s t r u c t u r a l d a t a on t h e t u n g s t e n c o m p o u n d s are, a t present, n o t available.
(ii) Halide Complexes
T h e complex hexafluoro anion AFg" h a s been isolated recently w i t h a v a r i e t y of cations: MoFg"; Li, N a , K , R b , Cs, Tl, N O , a n d WFg-: Li, N a , K , R b , Cs, N O . T h e p r e p a r a t i v e m e t h o d s used are t h e reduction of t h e hexafluorides w i t h M I in liquid s u l p h u r dioxide (Hargreaves a n d Peacock, 1 9 5 7 ; K e m m i t t et al., 1 9 6 3 ) , or t h e fluorination of t h e h e x a carbonyls in t h e presence of M F or M I w i t h iodine pentafluoride (Har
greaves a n d Peacock, 1 9 5 8 a ,c ) , or sulphur tetrafluoride. T h e l a t t e r r e a g e n t h a s also been used on m o l y b d e n u m ( I V ) oxide or sulphide ( K e m m i t t a n d S h a r p , 1 9 6 1 ; K e m m i t t et al., 1 9 6 3 ) . T h e nitrosyl salts
HALIDE CHEMISTRY OF CHROMIUM, MOLYBDENUM AND TUNGSTEN 269 a r e o b t a i n e d b y t r e a t i n g t h e m e t a l s w i t h N 0 F ( H F) 3 or m o l y b d e n u m hexafluoride w i t h nitric oxide (Geichman et al., 1962b, 1963; Seel et al., 1962).
T h e octafluorides KgMoFg a n d KgWFg h a v e b e e n isolated from t h e r e a c t i o n of a 2:1 m i x t u r e of A ( C 0) 6 a n d K I in iodine pentafluoride.
D o u b l e salts a r e also o b t a i n e d for R b a n d N a ( H a r g r e a v e s a n d P e a c o c k , 1958a,c; K e m m i t t a n d S h a r p , 1961).
T h e corresponding d a r k green chloro complexes of t h e p e n t a v a l e n t s t a t e a r e also k n o w n w i t h t h e cations E t 4 N for MoClg" a n d N a , K , R b , Cs, E t 4 N , Ph4As, Μθ4Α for WClg". T h e y h a v e b e e n p r e p a r e d from WCle-MCl or M I m e l t s (Vasil'kova et al, 1963a,b; Zaitseva, 1963;
Dickinson et al, 1964), b y r e a c t i n g MCI a n d t u n g s t e n hexachloride in t h i o n y l chloride ( A d a m s et al, 1963a; B a g n a l l et al, 1964), b y r e a c t i n g MCI a n d t u n g s t e n or m o l y b d e n u m p e n t a c h l o r i d e in chloroform (Brisdon a n d W a l t o n , 1965b), a n d b y h e a t i n g p o t a s s i u m t u n g s t a t e in c a r b o n t e t r a c h l o r i d e t o 400° (Dickinson et al, 1964). T h e h e p t a - a n i o n WCl72_
(K, R b , Cs) h a s also been r e p o r t e d as occurring in t h e WClg-MCl m e l t s (Vasil'kova et al, 1963a,b; Zaitseva, 1963). T h e black t u n g s t e n ( V ) h e x a b r o m i d e a n i o n h a s b e e n isolated w i t h t h e a m i n e bases Et4_^H„N (n = I —3) (Brisdon a n d W a l t o n , 1965a,b).
T h e complex halogeno-anions are s t a b l e w h e n d r y b u t a r e v e r y susceptible t o hydrolysis ( H a r g r e a v e s a n d P e a c o c k , 1957,1958c; A d a m s et al, 1963a; G e i c h m a n et al, 1963). T h e anions A X g ' , are r e a s o n a b l y s t a b l e t o h e a t , only L i W F g decomposing before 250-300° ( H a r g r e a v e s a n d P e a c o c k , 1957; A d a m s et al, 1963a; K e m m i t t et al, 1963). T h e c o m p o u n d s KWClg a n d K2WCI7 are r e p o r t e d as h a v i n g t h e low h e a t s of f o r m a t i o n —11-3 a n d —12-7 kcal mole-^ respectively (Zaitseva, 1963).
T h e t u n g s t e n ( V ) hexachloro anions a p p e a r t o be i n t e r c o n v e r t i b l e w i t h t h e t u n g s t e n ( I V ) complexes, in some cases e v e n a t r o o m t e m p e r a t u r e . T h e ease of i n t e r c h a n g e is in t h e o r d e r Κ > Cs > R b (Dickinson et al, 1964)
2MWC16 ^ MgWCle + WCle
T h e complex NOMoFg is r e d u c e d w i t h d i n i t r o g e n t e t r o x i d e t o NO2M0F5 (Geichman et al, 1962b).
T h e m a g n e t i c m o m e n t s of c e r t a i n of t h e complexes h a v e b e e n m e a s u r e d , often over a t e m p e r a t u r e r a n g e . Some of t h e s e values a r e listed in T a b l e X V I I I . T h e v a l u e s a r e low d u e t o a high s p i n - o r b i t coupling, b u t i n a d d i t i o n t h e r e a p p e a r s t o b e some a n t i f e r r o m a g n e t i c b e h a v i o u r p a r t i c u l a r l y for t h e t u n g s t e n c o m p o u n d s . KgMoFg h a s a m o m e n t of 1-23 Β a t r o o m t e m p e r a t u r e ( H a r g r e a v e s a n d Peacock, 1958c).
270 J. Ε . FERGUSSON
TABLE X V I I I . M a g n e t i c p r o p e r t i e s o f A X g
-C o m p o u n d μ{Β) θ R e f e r C o m p o u n d μ{Β) θ R e f e r
a t 2 5 ° e n c e s (25°) e n c e s
N a [ M o F e ] 1-66 2 1 8 ) 1 K[ W F e ] 0 - 5 - 0 - 6 1 2 0 )
R b [ M o F e ] 1-75 158 J 1 C s [ W F e ] 0 - 5 - 0 - 6 105 J 1
(C2H5)4N[MoCl6] 1-31 2 {C2H5)4N[WCle] 0 - 6 6 3 0 5 2, 3, 4
(C2H5)4N[WBre] 1-28 a N a i W C l e ] 0 - 8 8 5
( C 2 H 5 ) N H 3[WBre] 1-23 Ό C s [ W C l e ] 1 · 0 0 - Μ 7 105 3, 5
1, H a r g r e a v e s a n d P e a c o c k ( 1 9 5 8 b ) ; 2, B r i s d o n a n d W a l t o n ( 1 9 6 5 b ) ; 3, B a g n a l l et al.
( 1 9 6 4 ) ; 4, A d a m s et al. ( 1 9 6 3 ) ; 5, D i c k i n s o n et al. ( 1 9 6 4 ) ; 6, B r i s d o n a n d W a l t o n ( 1 9 6 5 a ) .
F r o m X - r a y p o w d e r d a t a i t h a s been shown t h a t NaMoFg is cubic (Mo—F = 1-74 A) ( E d w a r d s a n d Peacock, 1961) a n d NOMoFg is pseudo cubic (Geichman et al., 1962b, R a l s t o n a n d Musil, 1960). T h e s t r u c t u r a l t y p e a p p e a r s t o v a r y w i t h t h e cation as follows:
L i N a Κ Tl R b Cs
M o F r R i Τ R2 R2 R2
W F r τ R ,
where R i = rhombohedral (LiSbPg), Ci = cubic (NaSbFg), Τ = tetra
gonal (KNbFg), and Rg = rhombohedral (KOsFg) (Hargreaves and Peacock, 1957; K e m m i t t et al., 1963). KgMoFg is described as cubic (Hargreaves and Peacock, 1958c), while the complexes MWClg have similar, b u t more complicated structures than t h e cubic MgWClg (Dickinson et al., 1964).
The electronic absorption spectra of the MoClg", WClg" and WBrg-ions have been recorded, and appear complicated, which m a y be due t o some Jahn-Teller distortion (Dickinson et al., 1964; Brisdon and Walton, 1965a,b). Considerably more work is necessary in this field.
Lowfrequency infrared studies have led t o the following m e t a l -halogen stretching mode assignments.
MoFfi- 623, 615 cm-^ (Geichman et al, 1962b) WFe" 594 c m - i
WClfi- 329, 317, 305, 315 c m - i (Bagnall et al, 1964) (iii) Oxyhalides
The simple oxyhalides of the pentavalent state are n o t very well characterized, whereas salts derived from them are well known. There are no oxyfluorides MOF3 or MOgF. The oxychloride M0OCI3 has been prepared and characterized a number of times recently, in some cases rather poorly. I t is formed along with other products, in the electrolytic reduction of molybdenum(VI) oxide in hydrochloric acid (3M) (Babko
HALIDE CHEMISTRY OF CHROMIUM, MOLYBDENUM AND TUNGSTEN 271
a n d G e t ' m a n , 1959), or b y t h e chlorination of m o l y b d e n u m ( I V ) com
p o u n d s in air (Glukhov a n d B e k h t l e , 1958b; Schafer a n d Tillack, 1964).
Melts of m o l y b d e n u m ( V ) chloride a n d either m o l y b d e n y l chloride or m o l y b d e n u m ( V I ) oxide p r o d u c e t h e oxychloride as well as t h e m o r e volatile M0OCI4 (Glukhov a n d Eliseev, 1959, 1961b, 1962, 1963;
Eliseev, 1963). T h e p e n t a c h l o r i d e r e a c t s w i t h s u l p h u r dioxide or thionylchloride t o give M0OCI3, p r o b a b l y b y o x y g e n a b s t r a c t i o n ( E d w a r d s , D . Α., 1963; Colton a n d T o m k i n s , 1965). T h e simplest p r e p a r a t i o n a p p e a r s t o be t o h e a t t h e o x y t e t r a c h l o r i d e (M0OCI4) in a s t r e a m of n i t r o g e n a t 120° (Colton a n d T o m k i n s , 1965).
T h e corresponding t u n g s t e n c o m p o u n d m a y be one of t h e p r o d u c t s formed in t h e WClg-WOa m e l t ( S h c h u k a r e v et al, 1959b).
M o l y b d e n u m ( V ) o x y t r i b r o m i d e occurs as a m i n o r p r o d u c t of t h e b r o m i n a t i o n of m o l y b d e n u m m e t a l , p r e s u m a b l y t h r o u g h o x y g e n im
purities ( D u r a n d et al, 1959). A b r o m i n e - o x y g e n m i x t u r e m a y increase t h e yield. More recently, t h e c o m p o u n d w a s o b t a i n e d b y r e a c t i o n b e t w e e n m o l y b d e n y l b r o m i d e a n d p h o s p h o r u s p e n t a b r o m i d e in boiling CCI4, a n d purified b y s u b l i m a t i o n (Colton a n d T o m k i n s , 1965).
T h e b r o w n - b l a c k M0OCI3 (m.p. 295°) (Glukhov a n d Eliseev, 1959) c a n b e purified b y v a c u u m s u b l i m a t i o n (Colton a n d T o m k i n s , 1965), or b y e x t r a c t i o n of i m p u r i t i e s i n t o c a r b o n t e t r a c h l o r i d e (Glukhov a n d Eliseev, 1962). B o t h it a n d t h e o x y t r i b r o m i d e sublime a n d dissociate on h e a t i n g (200-215°). T h e p r o d u c t s of cissociation are m o l y b d e n u m ( V I ) oxyhalides a n d m o l y b d e n u m ( I I I ) halides. T h e c o m p o u n d s are suscep
tible t o m o i s t u r e , giving M02O3CI4 a n d M02O4CI2 as well as o x i d a t i o n p r o d u c t s . T h e oxychloride is q u i t e stable in acid solution ( B a b k o a n d G e t ' m a n , 1959; G l u k h o v a n d Eliseev, 1959, 1962; E d w a r d s , D.A., 1963;
Mitchell, 1963).
T h e low m a g n e t i c m o m e n t of t h e oxytrichloride (μ = 1-65 Β a t 295°) m a y be d u e t o a large s p i n - o r b i t coupling c o n s t a n t or t o a w e a k Mo—Mo i n t e r a c t i o n . T h e c o m p o u n d p r o b a b l y achieves sixfold coordination b y p o l y m e r i z a t i o n , a n d in solution b y solvation ( E d w a r d s , D . Α., 1963;
S h u s t o r o v i c h a n d A t o v m y a n , 1963). T h e M = 0 s t r e t c h i n g frequency a t 1020 c m- i is in t h e e x p e c t e d place, a n d t h e electronic a b s o r p t i o n spec
t r u m can be assigned on t h e basis of a n o c t a h e d r a l complex w i t h a s t r o n g t e t r a g o n a l d i s t o r t i o n ( E d w a r d s , D . Α., 1963) (13,700 cm-^
B^g -> Eg a n d 22,200 c m- i B^g -> B^^).
Some coordination complexes of t h e oxychloride are k n o w n of t h e t y p e M0OCI3.2L (L = e t h e r , m e t h a n o l , R C N , t e t r a h y d r o f u r a n , t r i p h e n y l p h o s p h i n e oxide, a n d -arsine oxide, etc.). T h e y a r e p r e p a r e d e i t h e r b y r e a c t i o n of t h e ligand w i t h m o l y b d e n u m ( V ) chloride, which p r o b a b l y involves solvolysis, or b y direct r e a c t i o n of t h e ligand a n d t h e
272 J. Ε. FERGUSSON
oxytrichloride ( W a r d l a w a n d W e b b , 1930; L a r s o n , 1960; F u n k et al, 1961 ; H o r n e r a n d T y r e e , 1962; E d w a r d s , 1965; F e e n a n a n d Fowles, 1965).
F o r e x a m p l e , t h e p r e p a r a t i o n of M o O C l 3 ( P h 3 P) 2 can b e r e p r e s e n t e d b y M0CI5 + P h g P O -> M0OCI3 + P h 3 P C l 2
M0OCI3 + 2 P h 3 P O -> MoOCl3(Ph3PO)2
E v e n in t h e complex MoCl5(Ph3AsO) t h e o x y g e n a p p e a r s t o b e a t t a c h e d m o r e t o t h e m e t a l t h a n t h e arsenic. A further r e a c t i o n in excess ligand gives Mo02Cl2(Ph3PO)2 ( H o r n e r a n d T y r e e , 1962, 1963). T h e c o m p o u n d s a p p e a r t o b e n o r m a l o c t a h e d r a l complexes w i t h a t e t r a g o n a l distortion.
I n a d d i t i o n , complexes MoCl3L(L = Me2S, EtgS, etc.) are k n o w n ( F e e n a n a n d Fowles, 1965), as well as M o 2 0 3 C l 4( d i p y) 2 a n d M02O4CI2 (dipy)2 formed from t h e h y d r o l y s i s p r o d u c t s of M0OCI3 (Mitchell, 1963).
T h e complex oxyfluoro anion MoOFg^- h a s b e e n isolated as t h e NH4 a n d Κ salts. T h e pale-green p o t a s s i u m salt, p r e p a r e d b y fusing K M o F ^ w i t h K H F 2 in a n i n e r t a t m o s p h e r e , is readily h y d r o l y s e d (Gmelin, 1935;
H a r g r e a v e s a n d Peacock, 1957). KgWOFg h a s also b e e n r e p o r t e d (Peacock, 1960).
T h e o x y chloro anions a r e m o r e a b u n d a n t a n d t h e r e are t w o t y p e s , AOClg^" a n d A0Cl4~. T h e y h a v e b e e n isolated w i t h t h e cations listed below:
M0OCI52- NH4, K , R b , Cs, P y H , MegNHa, MeNH3, C^HgN, D M F H McgNH.
M0OCI4- R b , Cs, NH4, p y H , CgH^N, Et2NH2, Me3NH.
WOCI52- R b , Cs, NH4, Μ θ 3 Ν Η , p y H , C^HgN, C6H5NH3 WOCI4- p y H , C , H s N .
T h e AOCls^- a n i o n is o b t a i n e d b y a d d i n g t h e c a t i o n t o a solution of M0CI5 or p o t a s s i u m o x a l a t o d i o x y t u n g s t a t e ( V ) in hydrochloric acid
(Allen et al., 1963), or from solvolysis p r o d u c t s of t h e p e n t a c h l o r i d e ( W a r d l a w a n d W e b b , 1930; S h c h u k a r e v a n d N o v i k o v , 1956; F u n k et al, 1961; Allen et al, 1962). R e d u c t i o n of t h e h e x a v a l e n t s t a t e h a s also been used ( J a m e s a n d W a r d l a w , 1927; Cooper a n d W a r d l a w , 1932; Simon a n d S o u c h a y , 1956; H e i m b u r g e r a n d R o h m e r , 1963; W e n d l i n g et al, 1963), a n d t h e oxychloride in hydrochloric acid is itself a r e a d y source of t h e a n i o n ( E d w a r d s , D . Α., 1963). T h e a n i o n WOCI4- is o b t a i n e d b y t h e first m e t h o d a b o v e for AOCls^-, w h e n large cations are used, w h e r e a s M0OCI4- is o b t a i n e d similarly using, however, s u l p h u r dioxide in place of hydrochloric acid. This a g a i n p r e s u m a b l y goes v i a a solvolysis re
a c t i o n (see p . 267) (Allen et al, 1963). Acetonitrile h a s also b e e n u s e d as t h e r e a c t i n g m e d i u m ( H o r n e r a n d T y r e e , 1963).
HALIDE CHEMISTRY OF CHROMIUM, MOLYBDENUM AND TUNGSTEN 273
T h e o x y b r o m o anions AOBrg^- a n d A O B r ^ - are formed in identical ways t o t h e oxychloro anions (Angell et at., 1929; Beck, 1931; G r a y , 1960; Garside a n d F r e n c h , 1962; Allen et al., 1963):
MoOBr^^- NH4, K , R b , Cs, p y H , CgHgN.
M o O B r ^ - Li?, p y H , C^HgN.
WOBrs^- NH4, R b , Cs.
W O B r ^ - p y H , C^HgN, i-C^HgN.
T h e complexes pyHiMoOgCla] a n d Li[Mo02Br2.2H20]4H20 h a v e also been r e p o r t e d ( J a m e s a n d W a r d l a w , 1927; Angell et al., 1929).
T h e complexes of t h e anions AOXg^- a n d A O X 4 - are green-yellow in colour, t e n d i n g t o b r o w n . T h e y are stable in d r y air b u t r a p i d l y hydrolyse in m o i s t u r e , t u r n i n g red, t h e n blue. Because of t h e large t e t r a g o n a l distortion imposed b y t h e M = 0 b o n d t h e spectral a n d m a g n e t i c properties of t h e complexes are of i n t e r e s t a n d h a v e been well studied. T h e m a g n e t i c m o m e n t s of t h e MoOXg^- complexes are close t o t h e spin-only value. T h e increase in t h e m o m e n t is p r o b a b l y d u e t o t h e t e t r a g o n a l distortion destroying t h e s p i n - o r b i t coupling. A n e s t i m a t e of t h e r e d u c t i o n of t h e coupling c o n s t a n t (for Mo(V)) is from 1030 t o 240 c m- i ( H a r e et al., 1962). A similar e x p l a n a t i o n m a y hold for M0OX4- w h e r e t h e r e will be obviously some distortion. T h e m a g netic m o m e n t s of t h e t u n g s t e n complexes are again higher t h a n ex
p e c t e d b u t lower t h a n t h e m o l y b d e n u m values because of t h e larger
TABLE
XIX.
M a g n e t i c p r o p e r t i e s o fAOXg^-
a n dAOX4-A n i o n Cation μ ( Β ) θ References
M0OCI52- R b 1-69 16 1
p y H 1-74 15
MoOBr^^- Cs 1-73 1
NH4
1-72 5 1WOCI52- R b 1-55 2 0 i
Cs 1-49 16
WOBr^^- R b 1-37
Cs 1-55 17
M0OCI4- p y H 1-73
1-73
M o O B r 4 - p y H 1-76 16 9
CgHgN 1-76 9
WOCI4- p y H 1-50 3
CgHgN I - 4 I
W 0 B r 4 - p y H 1-43
1
C e H s N 1-40 J
1, A l l e n et al. ( 1 9 6 3 ) ; 2, G a r s i d e a n d F r e n c h ( 1 9 6 2 ) ; 3, T j a b b e s ( 1 9 3 2 ) .
274 J. Ε. FERGUSSON
s p i n - o r b i t coupling c o n s t a n t (Figgis a n d Lewis, 1964). T h e m a g n e t i c m o m e n t s of a few r e p r e s e n t a t i v e c o m p o u n d s are given in Table X I X . W h e r e m e a s u r e d , t h e c o m p o u n d s obey t h e Curie-Weiss law.
T h e change in t h e m a g n e t i c susceptibility of t h e ion MoOCls^" in hydrochloric acid is interesting as it d r o p s w i t h acidity t o a m i n i m u m a t 2M HCl. This is p r o b a b l y d u e t o t h e formation of a d i a m a g n e t i c dimer [MoOClJgO^" a t low acidities (Sacconi a n d Cimi, 1954; J a k o b et al., 1961; G r a y a n d H a r e , 1962; H a i g h t , 1962; H a r e et al., 1962). A molecular orbital t h e o r y of t h e b o n d i n g in t h e species AOClg^- d e m o n s t r a t e s t h e d o m i n a t i n g effect of t h e A = 0 b o n d (Gray a n d H a r e , 1962) (Fig. 4). T h e electronic a b s o r p t i o n spectra of t h i s t y p e of oxychloride
Metal Oxygen and
orbitals chlorine Cr or Mo orbitals
πα * lKa*e*
// \
/ \
\ / / M
-^/$: ^^\\\
\ \ \ \ ^-N- 'AV\ T T (Oxygen)
\\\ \ \
\e^, JEo^t ^ —
cr bonding levels
FIG. 4. R e l a t i v e e n e r g i e s o f o n e - e l e c t r o n m o l e c u l a r o r b i t a l s f o r t h e A O C l g ^ " a n i o n ( A = C r , M o ) .
can be satisfactorily explained b y t h i s t h e o r y (Jorgensen, 1957; G r a y a n d H a r e , 1962; Allen et al, 1963; E d w a r d s , D . Α., 1963; H e i m b u r g e r a n d R o h m e r , 1963). F o r AOClg" (A = Cr, Mo) t h e b a n d s are assigned as shown in Table X X (Gray a n d H a r e , 1962). T h e spectra of t h e anions MoOBrg^-, WOCls^-, a n d WOBrg^-, however, do n o t a p p e a r t o fit e x a c t l y t h e a b o v e t h e o r y . I t is clear t h a t further refinements are neces
sary, p r o b a b l y t a k i n g a c c o u n t , in t h e case of t h e o x y b r o m i d e s , of t h e
HALIDE CHEMISTRY OF CHROMIUM, MOLYBDENUM AND TUNGSTEN 275
§
Ο
Α S œ ι> CO τ5
Ο Ο ^
Α Α s
ι> ο ^
Μ CO
Ο Ο Ο Α Α Α
c<r-1 c<i CO CO
ο ο S o ο" ÎO
CO CO
Ο Α Α Α 05 GO
EG OH
• S 02
276 J. Ε. FERGUSSON
TT-electrons of t h e halogen (Allen et al, 1963). T h e electronic a b s o r p t i o n s p e c t r u m of MoOCl4~ alters from solid t o solution a n d t h i s change m a y be d u e t o different e n v i r o n m e n t s . E v i d e n c e for intra-ion i n t e r a c t i o n in t h e solid h a s been found in t h e infrared, w h e r e t h e M o = 0 s t r e t c h i n g b a n d is split (1000-960 c m - i ) (Allen et al, 1963). O t h e r oxyhalogeno-anions also h a v e t h e A — 0 s t r e t c h i n g m o d e a r o u n d 1000 cm-^ a n d A—Cl a t 324 a n d 306 cm-^ for A = Mo a n d W respectively (Barra
clough, et al, 1959; H o r n e r a n d T y r e e , 1963; B r o w n , 1964). T h e e.s.r.
s p e c t r a of M0OCI3 a n d MoOClg^- h a v e been recorded a n u m b e r of t i m e s (Garif'yanov a n d P e d o t o v , 1962a,b; H a r e et al, 1962; G a r i f ' y a n o v et al, 1963).
N o t h i n g is k n o w n of t h e s t r u c t u r e s of t h e c o m p o u n d s e x c e p t t h a t CsaLAOClg] is said t o h a v e t h e s a m e u n i t cell size as AClg^" (Brown, 1964).
F. Molybdenum and tungsten(VI) (d')