Syntheses and properties of new layered alkali-metal/ammonium vanadium(V) methylphosphonates: M(VO2)(3)(PO3CH3)(2) (M=NH4,K,Rb,Tl). Single-crystal structures of K(VO2)(3)(PO3CH3)(2) and NH4(VO2)(3)(PO3CH3)(2)

The hydrothermal syntheses of a family of new alkali-meta/ammonium vanadium(V) methylphosphonates, M(VO2)(3)(PO3CH3)(2) (M = K, NH4, Rb, Tl), are described. The crystal structures of K(VO2)(3)(PO3H3)(2) and NH4(VO2)(3)(PO3CH3)(2) have been determined from single-crystal X-ray data. Crystal data: K(VO2)(3)(PO3CH3)(2), M(r)= 475.93, trigonal, R32 (No. 155), a 7.139(3) Angstrom, c = 19.109(5) Angstrom, Z = 3; NH4(VO2)(3)(PO3CH3)(2), M(r) = 454.87, trigonal, R32 (No. 155), a 7.150(3) Angstrom, c = 19.459(5) Angstrom, Z = 3. These isostructural, noncentrosymmetric phases are built up from hexagonal tungsten oxide (HTO) like sheets of vertex-sharing VO6 octahedra, capped on both sides of the V/O sheets by PCH3 entities (as [PO3CH3](2-) methylphosphonate groups). In both phases, the vanadium octahedra display a distinctive two short + two intermediate + two long V-O bond distance distribution within the VO6 unit. Interlayer potassium or ammonium cations provide charge balance for the anionic (VO2)(3)(PO3CH3)(2) sheets. Powder X-ray, TGA, IR, and Raman data for these phases are reported and discussed. The structures of K(VO2)(3)(PO3CH3)(2) and NH4(VO2)(3)(PO3CH3)(2) are compared and contrasted with related layered phases based on the HTO motif.