BANBF7-X(OH)X - PREPARATION AND CRYSTAL-STRUCTURE

The compound BaNbF7-x(OH)x has been prepared at moderate temperature i n a PTFE beaker from HF aqueous solutions. It crystallizes m the cubic system, space group Pa3BAR (n-degrees 205) with a = 9.9259(5) angstro m, Z = 8. The structure has been determined by X-Ray diffraction data from a single crystal leading to R = 0.0199 and R(w) = 0.0194 for 337 independent reflections and 29 parameters. The tridimensional network is constituted of NbX7 (X = F, OH) isolated monocapped trigonal prisms . Two kinds of Ba2+ cations are located respectively in rhombododecahe dra (CN = 14) and in cubooctahedra (CN = 12); the connection between t hese polyhedra and the NbX7 (X = F, OH) groups is discussed.