Acta Cryst. (2009). C65, i1-i6 [ doi:10.1107/S0108270108036755 ]
Abstract: As part of a continuing study of oxyfluorotellurates(IV), materials likely to present interesting nonlinear optical properties, two new phases, titanium(IV) tellurium(IV) trioxide difluoride, TiTeO3F2, and divanadium(IV) ditellurium(IV) heptaoxide difluoride, V2Te2O7F2, have been characterized and present, respectively, titanium and vanadium in the tetravalent state. The TiTeO3F2 structure is based on linear double rows of TiO3F3 polyhedra sharing vertices. These rows are connected to adjacent rows via two vertices of Te2O5 bipolyhedra. The Te, Ti, one F and two O atoms are on general positions, with one O and F statistically occupying the same site with half-occupancy for each anion. One O and one F occupy sites with .m. symmetry. The V2Te2O7F2 structure consists of zigzag chains of VO4F2 octahedra alternately sharing O-O and F-F edges. These chains are connected via Te2O5 bipolyhedra, forming independent mixed layers. The Te, V, one F and three O atoms are on general positions while one O atom occupies a site of 
symmetry. In both phases, the electronic lone pair E of the TeIV atom is stereochemically active. A full O/F anionic ordering is observed in V2Te2O7F2, but in TiTeO3F2 one of the six anionic sites is occupied by half oxygen and half fluorine, all the others being strictly ordered. These compounds represent new members of a growing family of oxyfluorotellurates(IV), including the recently characterized members of formula MTeO3F, M being a trivalent cation. As was true for the previous members, they are characterized by an unusually high thermal and chemical stability in relation to the absence of direct Te-F bonds.
Formula: TiTeO3F2 and V2Te2O7F2
 |   Structure factor file (CIF format) (56.8 kbytes) |
| Structure factor file (CIF format) (48.3 kbytes) |
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