SYNTHESES, CRYSTAL-STRUCTURES, AND PROPERTIES OF NEW LAYERED TUNGSTEN(VI)-CONTAINING MATERIALS BASED ON THE HEXAGONAL-WO3 STRUCTURE - M(2)(WO3)(3)SEO3 (M=NH4,RB,CS)

The hydrothermal syntheses and crystal structures of (NH4)(2)(WO3)(3)S eO3 and Cs-2(WO3)(3)SeO3, two new noncentrosymmetric, layered tungsten (VI)-containing phases are reported. Infrared, Raman, and thermogravim etric data are also presented. (NH4)(2)(WO3)(3)SeO3 and Cs-2(WO3)(3)Se O3 are isostructural phases built up from hexagonal-tungsten-oxide-lik e, anionic layers of vertex-sharing WO6 octahedra, capped on one side by Se atoms (as selenite groups). Interlayer NH4+ or Cs+ cations provi de charge balance. The full II-bonding scheme in (NH4)(2)(WO3)(3)SeO3 has been elucidated from Rietveld refinement against neutron powder di ffraction data. The WO6 octahedra display a 3 short + 3 long W-O bond- distance distribution within the WO6 unit in both these phases. (NH4)( 2)(WO3)(3)SeO3 and Cs-2(WO3)(3)SeO3 are isostructural with their molyb denum(VI)-containing analogues (NH4)(2)(MoO3)(3)SeO3 and Cs-2 (MoO3)(3 )SeO3. Crystal data: (NH4)(2)(WO3)(3)SeO3, M(r) = 858.58, hexagonal, s pace group P6(3) (No. 173), a = 7.2291(2) Angstrom, c = 12.1486(3) Ang strom, V = 549.82(3) Angstrom(3), Z = 2, R(p) = 1.81%, and R(wp) = 2.2 9% (2938 neutron powder data). Cs-2(WO3)(3)SeO3, M(r) = 1088.31, hexag onal, space group P6(3) (no. 173), a = 7.2615(2) Angstrom, c = 12.5426 (3) Angstrom, V = 572.75(3) Angstrom(3), Z = 2, R(p) = 4.84%, and R(wp ) = 5.98% (2588 neutron powder data). (C) 1995 Academic Press, Inc.