CaM2(PO4)2(HPO4)(M = Fe or V): phosphates containing dimers of edge-sharing MO6 octahedra

Abstract

Two new phosphates, CaM₂(PO₄)₂(HPO₄)(M = Fe^III or V^III), have been synthesised hydrothermally at 400 °C and characterized by single-crystal X-ray diffraction. Crystal data: CaFe₂(PO₄)₂(HPO₄), monoclinic, space group P2₁/n, a= 6.3663(6), b= 19.752(2), c= 6.5030(8)Å, β= 91.626(9)°, 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)Å, β= 91.51(1)° 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 Mössbauer studies.