Synthesis and crystal structure of sigma-Zn0.25V2O5 center dot H2O with a novel type of V2O5 layer

A new layered vanadium bronze designated as sigma-phase Zn0.25V2O5 . H2O has been hydrothermally synthesized from ZnCl2 and VO(OH)(2). A single-crystal study revealed the triclinic system <P(1)over bar>: a = 10.614(2) Angstrom, b = 8.031(3) Angstrom, c = 10.7688(9) Angstrom, alpha = 90.65(1)degrees, beta = 91.14(1)degrees, gamma = 90.09(2)degrees, and Z = 8, The structure was solved and refined to R/R(w) = 0.079/0.048 for 1580 reflections with I > 3 sigma(I), which consists of V2O5 layers stacking along the c axis and interstitial hydrated Zn2+ ions. The V2O5 layer adopts a novel polyhedral framework built up of VO6 octahedra, VO5 trigonal bipyramids, and VO4 tetrahedra, When projected parallel to the ab plane, the V2O5 layer is described by the atomic sheet model in a manner similar to the V2O5 layer of delta phase such as delta-AgxV2O5, that is, a double-sheet type composed of two V2O5 sheets facing each other. The interstitial Zn atom forms a ZnO6 octahedron with two apical oxygens of the VO4 tetrahedra on opposide sides and with four coplanar water molecules. The anhydrous sigma phase was obtained by heating the hydrate up to 200 degrees C accompanied by the contraction in layer spacing from 10.76 to 8.92 Angstrom. (C) 1996 Academic Press, Inc.