Hydrothermal syntheses and crystal structures of new layered tungsten(VI) methylphosphonates, M(2)(WO3)(3)PO3CH3 (M=NH4, Rb, Cs)

The hydrothermal syntheses of Cs-2(WO3)(3)PO3CH3, Rb-2(WO3)(3)PO3CH3 and (NH4)(2)(WO3)(3)PO3CH3, three new noncentrosymmetric, layered tungsten(VI)-containing phases, are described. The crystal structures of Cs-2(WO3)(3)PO3CH3 and (NH4)(2)(WO3)(3)PO3CH3 were refined by using Rietveld analysis of powder diffraction data. These phases are built up from hexagonal tungsten-oxide-libe 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: Cs-2(WO3)(3)PO3CH3, M(r) = 1055.36, trigonal, space group R3 (no. 146), a = 7.25791(9) Angstrom, c = 20.2762(4) Angstrom, V = 925.00(4) Angstrom(3), Z = 3, R(p) = 2.37%, R(wp) = 3.12% (2943 neutron powder data). (NH4)(2)(WO3)(3)PO3CH3, M(r) = 825.63, trigonal, R3 (no. 146), a = 7.22851(7) Angstrom,c = 19.3471(3) Angstrom, V = 875.48(3) Angstrom(3), Z = 3, R(p) = 8.14%, R(wp) = 10.12% (2665 X-ray powder data).