Ab-initio powder structure determination of CaBa2(HPO4)2(H2PO4)2:: a new phosphate with a M(TΦO4)4 chain structure

The crystal structure of CaBa2(HPO4)(2)(H2PO4)(2) has been solved ab-initio from X-ray powder data. CaBa2(HPO4)(2)(H2PO4)(2) crystallizes in the monoclinic system (space group P2(1)/a - No 14, Z = 2) with a = 12.3872(2) Angstrom, b = 10.2046(1) Angstrom, c = 5.4946(1) Angstrom, beta = 100.767(1)degrees. The X-ray powder diffraction pattern data were refined by the Rietveld profile technique to R-Bragg = 0.06. The crystal structure of CaBa2(HPO4)(2)(H2PO4)(2) is built up from [HPO4] and [H2PO4] tetrahedra, [CaO6] octahedra and [BaO9] polyhedra linked tridimensionally by corners and/or edges. The structure consists of infinite chains Ca[H2P(2)O-4](2)[HP(1)O-4](2) running parallel to the c axis. These chains are linked together by 9-coordinated Ba2+ ions.