Some reactions of tungsten and rhenium halides.

The preparation and some reactions of chloride fluorides of tungsten(VI) (of the type WC1nF6-n) have been studied. Values for the heat of formation of liquid tungsten chloride pentafluoride and tungsten dichloride tetrafluoride of -387 + 5 kcals/mole and -350 + 7 kcals/mole respectively, have been calculated from measured values of the heat of hydrolysis of the compounds and known thermochemical data. These values have led to some discussion as to the relative strength of the W-F bond (and similarly the W-C1 bond) in tungsten(VI) chloride fluoride compounds. Unsuccessful attempts have been made to separate the cis and trans isomers of tungsten dichloride tetrafluoride by both physical and chemical means. The 19F spectrum of WC12F4 consists of two triplets (in the ratio of 1:1) and a singlet, which indicates the presence of respectively the cis and trans isomers. In all experiments the 19F spectrum of the volatile products have shown the ratio of the WC12F4 isomers to still be the same. It has therefore been suggested that the cis and trans isomers of tungsten dichloride tetrafluoride are in dynamic equilibrium and cannot be separated. Preliminary investigations of the low temperature exchange reactions between rhenium hexafluoride and the boron trihalides, BC13 and BBr3; both in the presence and absence of free halogen, have resulted in solid products which are believed to be rhenium pentachloride and rhenium tetrabromide respectively. A value for the heat of formation of rhenium pentachloride of -85 + 5 kcals/mole has been calculated. The heats of formation of XeF2, SbF5 and XeF2.2SbF5 proved difficult to obtain, possibly due to the fact that though the predominant products of hydrolysis were those expected, small quantities of other compounds - obtained by secondary reactions - may also have been present. A melting point of 63C and a boiling point of 220 + 5C. were measured for pure XeF2.2SbF5.