Synthesis and structure of a new germanate fluoride: NaCa2GeO4F

We report the synthesis and structural characterization of a new oxoanion h alide, NaCa2GeO4F. Crystal data: FW = 235.74, Pnma (No. 62), orthorhombic, a = 5.362(2), b = 7.328(3), c = 12.681(4) Angstrom, V = 498.3(3) Angstrom ( 3), Z = 4, R(F) = 0.044, R-w(F) = 0.046 for 404 averaged reflections. Compo sitionally, this material can be viewed as the end-member of the hypothetic al solid solution Ca2GeO4 . (CaO)(1-x) . (NaF)(x). However, in this unusual oxyfluoride, the fluoride ion orders and fully occupies one anion site. Th e structure consists of complicated condensed chains of six-coordinated cat ions centered by fluoride ions and linked by chains of isolated germanium o xide tetrahedra. The structure is best described in terms of the anion pack ing rather than the packing of cation-centered coordination polyhedra. (C) 2001 Academic Press.