CAM2(PO4)2(HPO4) (M=FE OR V) - PHOSPHATES CONTAINING DIMERS OF EDGE-SHARING MO6 OCTAHEDRA

Two new phosphates, CaM2(PO4)2(HPO4) (M = Fe(III) or V(III)), have been synthesised hydrothermally at 400-degrees-C and characterized by single-crystal X-ray diffraction. Crystal data: CaFe2(PO4)2(HPO4), monoclinic, space group P2(1)/n, a = 6.3663(6), b = 19.752(2), e = 6.5030(8) angstrom, beta = 91.626(9)-degrees, Z = 4 and R = 0.0240; CaV2(PO4)2(HPO4), as above except a = 6.359(2), b = 19.973(2), c = 6.4744(4) angstrom, beta = 91.51 (1)-degrees and R = 0.0390. The two compounds are isostructural. The framework consists of corner-sharing PO4 tetrahedra, HPO4 groups and dimers of edge-sharing MO6 octahedra forming M2O10 units. The structure of CaFe2(PO4)2(HPO4) was further defined by thermogravimetric and Mossbauer studies.