Niobium trifluoride, structure

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. 

In contrast with the difluorides, the distribution of trifluorides extends to the third series of the transition metals, where iridium and gold trifluorides are fully characterized. In the second series, trifluorides are known for the elements from niobium to rhodium, with the exception of technetium, and in the first series, from titanium to cobalt. All the trifluorides have been characterized structurally, with earlier reports based on X-ray powder-diffraction data, since the compounds were not prepared in single-crystal form until more recently, when high-temperature, crystal-growth techniques became available. 

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