SYNTHESES, CRYSTAL-STRUCTURES, AND PROPERTIES OF NEW LAYERED ALKALI-METAL MOLYBDENUM(VI) METHYLPHOSPHONATES - CS-2(MOO3)(3)PO3CH3 AND RB-2(MOO3)(3)PO3CH3

The hydrothermal syntheses and crystal structures of two new alklali-m etal molybdenum(VI) methylphosphonates, CS2(MoO3)(3)PO3CH3 and Rb-2(Mo O3)(3)PO3CH3, are described. These isostructural phases are built up f rom hexagonal tungsten oxide like layers of vertex-sharing MoO6 octahe dra, capped on one side by P-CH3 entities (as [PO3CH3](2-)methylphosph onate groups). Interlayer Cs+ or Rb+ cations provide charge balance fo r the anionic sheets. The MoO6 octahedra display a distinctive three s hort + three long Mo-O bond distance distribution within the MoO6 unit . Powder X-ray, infrared, Raman, and thermogravimetric data for CS2(Mo O3)(3)PO3CH3 are also presented. The structures of Cs-2(MoO3)(3)PO3CH3 and Rb-2(MoO3)(3)PO3CH3 are related to those of the recently reported M(2)(MoO3)(3)SeO3 (M = NH4, Cs) materials but show a three-layer repe ating motif, rather that the two-layer repeat found in the M(2)(MoO3)( 3)SeO3 structures. This different layer repeat pattern may be correlat ed with the steric effect of the methylphosphonate group. Crystal data : Cs-2(MoO3)(3)PO3CH3, trigonal, R3 (No. 146), a = 7.304(2) Angstrom, c = 20.02(1) Angstrom, V = 924.7 Angstrom(3), Z = 3; Rb-2(MoO3)(3)PO3C H3, trigonal, R3 (No. 146), a = 7.307(2) Angstrom, c = 20.040(4) Angst rom, V = 926.7 Angstrom(3), Z = 3.