NOVEL CRYSTALLINE MICROPOROUS TRANSITION-METAL PHOSPHITES M11(HPO3)8(OH)6 (M = ZN, CO, NI) - X-RAY-POWDER DIFFRACTION STRUCTURE DETERMINATION OF THE CO AND NI DERIVATIVES

Crystalline microporous phosphites of transition metal ions, M11(HPO3)8(OH)6 (M = Zn, Co, Ni), have been synthesized through soft hydrothermal treatments. The crystal structures of the cobalt and nickel derivatives have been determined by refinement of X-ray powder diffraction data. The cell is hexagonal for both cobalt and nickel compounds (space group P63mc, Z = 1) with a = 12.8244 (4) angstrom, c = 4.9734 (2) angstrom, and a = 12.6329 (4) angstrom, c = 4.9040 (2) angstrom, respectively. The structure was refined with the Rietveld method, using as a starting model the parameters of the isostructural compound Zn11(HPO3)8(OH)6. The hexagonal structure can be thought of as a pseudomorphic variety of that of dumortierite. It is constructed from zig-zag pyroxene like chains of cationic edge-sharing octahedra which fuse by face-sharing to give double chains. Further connectivity of these double chains through corners results in an open tubular framework in which triangular and hexagonal channels run along the c axis. The anionic phosphite moieties are located inside the channels. No empty space remains in the smaller triangular ones but the location of phosphite groups on the walls of the bigger hexagonal tunnels occurs in such a way that empty infinite chains of H-6 face-sharing octahedra result. A strategy of synthesis, which takes into account the hydrolysis of the cationic species, is presented.