Hydrothermal syntheses and crystal structures of new layered tungsten(VI) methylphosphonates, M2(WO3)3PO3CH3(M = NH4, Rb, Cs)

Abstract

The hydrothermal syntheses of Cs₂(WO₃)₃PO₃CH₃, Rb₂(WO₃)₃PO₃CH₃ and (NH₄)₂(WO₃)₃PO₃CH₃, three new non-centrosymmetric, layered tungsten(VI)-containing phases, are described. The crystal structures of Cs₂(WO₃)₃PO₃CH₃ and (NH₄)₂(WO₃)₃PO₃CH₃ were refined by using Rietveld analysis of powder diffraction data. These phases are built up from hexagonal tungsten-oxide-like layers of vertex-sharing WO₆ groups, capped by P—CH₃ entities (as methylphosphonate groups) on one side of the tungsten oxide layer. Caesium, rubidium or ammonium cations provide interlayer charge compensation for the anionic layers. IR, Raman and thermogravimetry (TG) data for these phases are also presented. Crystal data: Cs₂(WO₃)₃PO₃CH₃, M_r= 1055.36, trigonal, space group R3 (no. 146), a= 7.25791(9)Å, c= 20.2762(4)Å, V= 925.00(4)ų, Z= 3, R_p= 2.37%, R_wp= 3.12%(2943 neutron powder data). (NH₄)₂(WO₃)₃PO₃CH₃, M_r=825.63, trigonal, R3 (no. 146), a= 7.22851(7)Å, c= 19.3471(3)Å, V= 875.48(3)ų, Z= 3, R_p= 8.14%, R_wp= 10.12%(2665 X-ray powder data).