Crystal structure and properties of Na2WO(PO4)2, the new vanadyl(IV)phosphates M=Ca and Sr

Two new complex vanadyl(IV)phosphates Na2MVO(PO4)(2) (M = Ca, Sr) were synthesized in evacuated quartz ampoules and investigated by means of X-ray diffraction, electron microscopy, DTA, ESR and magnetic susceptibility measurements. The crystal structure of Na2SrVO(PO4)(2) was solved ab initio from X-ray powder diffraction data. Both compounds are isostructural: a = 10.5233(3) Angstrom, b = 6.5578(2) Angstrom, c = 10.0536(3) Angstrom and a = 10.6476(3) Angstrom, b = 6.6224(2) Angstrom, c = 10.2537(3) Angstrom for Ca and Sr, respectively; S.G. Pnma, Z = 4. The compounds have a three-dimensional structure consisting of V4+ O-6 octahedra connected by PO4 tetrahedra via five of the six vertexes forming a framework with cross-like channels. The strontium and sodium atoms are located in the channels in an ordered manner. Electron diffraction as well as high-resolution electron microscopy confirmed the structure solution. The new vanadylphosphates are Curie-Weiss paramagnets in a wide temperature range down to 2 K with theta = 12 and 5 K for Ca and Sr phases, respectively. (C) 2004 Elsevier Inc. All rights reserved.