Metal hexahalide

The metal hexahalides MoFe, WFe, UF6 and WC are strong oxidants which are commercially available and soluble in various organic solvents, but the hexafluorides are readily hydrolyzed to the extremely corrosive and dangerous HF, and have therefore been little used. The standard redox potential of WCl6 is around 1.1 V relative to FeCp2 [222, 223] and it oxidizes [N(C6H4Br-4)3] to [N(C6H4Br-4)3][ WCle] [224]. 

For molecules with low polarity like hydrocarbons, electrostatic forces have only a minor influence. Molecules with highly polar bonds behave as dipoles or multipoles and exhibit corresponding interactions. For instance, hexahalide molecules like WF6 or WC16 are multipoles, the halogen atoms bearing a negative partial charge -q, while the metal... 

Finally, it is of interest to compare the estimates of covalency contributions for Ir(IV) hexahalides deduced by Allen et al. (11) from spectroscopic data, with those obtained by Owen and Thornley (85, 86) from ESR results. These latter authors attributed the reduction of below the free-ion value, entirely to symmetry restricted covalency, deriving the expression 0bsd = N (Cd +s , >), where the normalising constant, N , is equal to (1 —4a S + and [Pg.153]

Sulphur Hexafluoride, SF6.—Sulphur hexafluoride, the first hexahalide to be discovered, is prepared by submitting sulphur to the action of fluorine in a copper tube. The issuing gas on condensation in a spiral tube of the same metal at —80° C. becomes partly solidified by allowing the solid to vaporise gradually and passing the vapours through potassium hydroxide solution and solid potassium hydroxide successively, the substance is rendered purer, complete purification being effected subsequently by re-solidification followed by fractional evaporation.4... 

Selenium hexafluoride, SeFg, the only clearly defined hexahalide, is formed by reaction of fluorine with molten selenium, It is more reactive than the corresponding sulfur compound, SFs, undergoing slow hydrolysis. Selenium forms tetrahalides with fluorine, chlorine, and bromine, and dihalides with chlorine and bromine. However, other halides can be found in complexes, e.g,. treatment of the pyridine complex of SeF/i in ether solution with HBr yields (py)2SeBrc Selenium tetrafluoride also forms complexes with metal fluorides, giving MSeF complexes with the alkali metals. 

Unfortunately, a way has not been found to exploit hexahalide complexes of Fe2+ for this purpose. The divalent ion is unstable towards oxidation in aqueous solution it aquates too rapidly for successful incorporation as the desired hexachloride complex and it forms strong coordination complexes with gelatin, the peptizer of choice for practical applications. Such reactions prevent its incorporation into emulsion grains in a controlled manner. Despite the recent contention that the lower valence states of many transition-metal ions could fulfill the functions of Fe2+ [193], similar problems with incorporation have also frustrated their commercial application. This is especially true of Pt2+ and Pd2+, which showed much promise in single crystal studies [177,208]. 

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