STRUCTURAL FEATURES OF THE REACTIVES SITES IN ALPHA-M(DPO4)(2)CENTER-DOT-D2O (M=TI,ZR,PB) - HYDROGEN-BOND NETWORK AND FRAMEWORK

摘要

Three crystalline layered metal (IV) acid phosphates alpha-M(DPO4)(2) D2O, alpha-MP, (M = Zr, Ti, Pb) have been hydrothermally synthesized and the size and shape of the microparticles have been analyzed by the Scherrer method. The crystal structures of alpha-ZrP and alpha-TiP have been refined from a combined X-ray and neutron powder diffraction study by the Rietveld method. These hydrogen phosphates are isomorphous and belong to the alpha-ZrP-type structure. However, this precise powder diffraction study has shown that the frameworks and hydrogen-bond networks of these materials are slightly different. The unit cell volume of alpha-ZrP is larger than that of alpha-TiP because the layers in alpha-ZrP are less corrugated than those in alpha-TiP. The H-bond network is also slightly different, as in alpha-ZrP there is not H bonding between the layers, the shortest contact being O(7)... D(4) of 2.56(3) Angstrom. For alpha-TiP this contact is much shorter, 2.33(2) Angstrom, which may indicate a small but not negligible H-bond interaction between layers. Moreover, the intralayer H bonds are weaker in alpha-ZrP than in alpha-TiP as evidenced in the O(4)... D(3) interactions of 2.41(3) and 2.16(2) Angstrom, respectively. (C) l996 Academic Press,Inc. [References: 17]