Hydrothermal Synthesis and Crystal Structure of CaIn2(PO4)2(HPO4): An octahedral-tetrahedral framework ternary calcium indium(III) phosphate

The new ternary calcium indium(III) phosphate CaIn₂(PO₄)₂(HPO₄) with mixed octahedral-tetrahedral framework was synthesized through hydrothermal reaction of stoichiometric amounts of CaO and InCl₃ with excess of H₃PO₄ and H₂O at pH = 1. Single crystal x-ray diffraction studies show the compound to crystallize in monoclinic symmetry, space group P2₁/n (#14) with a = 657.08(6), b = 2023.7(2), c = 665.72(7) pm, β = 91.20(1)°, Z = 4 and R = 0.043. The framework is built up of dimers of edge-sharing InO₆ octahedra forming In₂O₁₀ units sharing all their OXO ligands with PO₄ tetrahedra, and HPO₄ groups.