Tantalum trifluoride, structure

This simple structure originally was assigned by Gutmann and Jdck 122) to the trifluorides of molybdenum and tantalum and later to NbFa... 

The observations made for the trifluorides of molybdenum, niobium and tantalum let it seem doubtful, whether the compound ZrFs, the formula of which was affirmed by chemical analysis, really crystallizes in a ReOs-type structure, as has been tentatively stated 95). The Zr—F-distance of 1.98 A calculated from the reported lattice constant ( =3.96A) is conspicuously small and would 5ueld a Zrs+ ionic radius of 0.65 A only. Therefore the Zr—F—Zr-chains, linear in the ReOs-type, should rather be angled as in the VF8-t e. 

Although the number of tetrafluorides reported is as large as the number of di- and trifluorides (see Table III), this group of compounds is the least well characterized structurally of the transition metal fluorides. The synthesis of most of the expected tetrafluorides has been reported, with examples from titanium to manganese in the first, from zirconium to palladium (except for technetium) in the second, and from hafnium to platinum (except for tantalum) in the third series. Many of them have been little studied and, in general, they have not proved amenable to crystallographic structural analysis. 

Xenon difluoride reacts also with some halosubstituted alkanes18,19 at room temperature in chloroform, carbon tetrachloride, dichloromethane or bromoform, and depending on the nature of the solvent used chloro or bromo derivatives are isolated with imidazo-(l,2-fr)-pyridazine18. Carbon tetrachloride reacts with xenon difluoride at 180°C, while room-temperature transformations are achieved when various catalysts [antimony trifluoride, tantalum(V) fluoride or silica dioxide] are used, whose structure also influences the product distribution20. Tris(fluorosulfonyl)methane gives a fluoro-substi-tuted product in its reaction with xenon difluoride in difluorodichloromethane21. 

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