Synthesis and structure of a new germanate fluoride:: NaCa2GeO4F

We report the synthesis and structural characterization of a new oxoanion halide, 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. Compositionally, this material can be viewed as the end-member of the hypothetical solid solution Ca2GeO4 . (CaO)(1-x) . (NaF)(x). However, in this unusual oxyfluoride, the fluoride ion orders and fully occupies one anion site. The structure consists of complicated condensed chains of six-coordinated cations centered by fluoride ions and linked by chains of isolated germanium oxide tetrahedra. The structure is best described in terms of the anion packing rather than the packing of cation-centered coordination polyhedra. (C) 2001 Academic Press.