Crystal structure and properties of the new vanadyl(IV)phosphates Na2MVO(PO4)2, M=Ca and Sr

Two new complex vanadyl(IV)phosphates Na 2 M VO(PO 4 ) 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 Na 2 SrVO(PO 4 ) 2 was solved ab initio from X-ray powder diffraction data. Both compounds are isostructural: a =10.5233(3) A, b =6.5578(2) A, c =10.0536(3) A and a =10.6476(3) A, b =6.6224(2) A, c =10.2537(3) A for Ca and Sr, respectively; S.G. Pnma , Z =4. The compounds have a three-dimensional structure consisting of V 4+ O 6 octahedra connected by PO 4 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 θ =12 and 5 K for Ca and Sr phases, respectively.