Two new lithium uranyl tungstates Li2(UO2)(WO4)2 and Li2(UO2)4(WO4)4O with framework based on the uranophane sheet anion topology

Two new lithium uranyl tangstates Li(UO2)(WO4)(2) and Li-2(UO2)(4)(WO4)(4)O have been prepared by high-temperature solid state reactions of Li2CO3, U3O8 and WO3. For each compound, the crystal structure was determined by single crystal X-ray diffraction data. using a Brucker diffractometer, equipped with a SMART CCD detector and MoKalpha radiation. The crystal structures were solved at room temperature by direct methods followed by Fourier difference techniques, and refined by a least square procedure on the basis of F-2 for all independent reflections, to R-1 = 0.035 for 65 refined parameters and 807 reflections with Igreater than or equal to2sigma(I) for Li-2(UO2)(WO4)(2) and to R-1 = 0.051 for 153 refined parameters and 1766 reflections with Igreater than or equal to2sigma(I) for Li-2(UO2)(4)(WO4)(4)O. The crystal structure of Li-2(UO2)(WO4)(2) is formed by perovskite sheets of WO6 octahedra, one octahedron thickness, connected together by (UO5)(infinity) infinite chains, and creating tunnels parallel to the c-axis. The lithium atoms are localized in the tunnels. The structure can be deduced from that of UMO5 (M = Mo, V, Nb) compounds by the replacement of half U atoms by Li. The crystal structure of Li-2(UO2)(4)(WO4)(4)O consists of UO7 pentagonal bipyramids, UO6 tetragonal bipyramids and WO6 distorted octahedra linked together to form a three-dimensional framework creating paralleled channels filled with lithium cations. The structure can also be described by the stacking of layers with the uranophane sheet anion topology similar to those obtained in UMO5 (M = Mo, V, Nb, Sb) compounds with an ordered population of pentagons by U and Li and of squares by U and W. The measured conductivities are comparable to those of the better Li+ ion conductor solid electrolytes such as LISICON or Li-beta-alumina. Crystallographic data: Li-2(UO2)(WO4)(2), orthorhombic symmetry, space group Pbcn and unit cell parameters a = 7.9372(15) Angstrom, b = 12.786(2) Angstrom, c = 7.4249(14) Angstrom, rho(cal) = 6.87(2) g/cm(3), rho(mes) = 6.89(1) g/cm(3) and Z = 4. Li-2(UO2)(4)(WO4)(4)O, monoclinic symmetry, space group C2/c and unit cell parameters a = 14.019(4) Angstrom, b = 6.3116(17) Angstrom, c = 22.296(6) Angstrom, beta = 98.86(3)degrees, rho(cal) = 7.16(2) g/cm(3), rho(mes) = 7.25(3) g/cm(3) and Z = 4. (C) 2004 Elsevier Inc. All rights reserved.