Crystal structures of hydrated vanadium oxides with delta-type V2O5 layers: delta-M0.25V2O5 center dot H2O, M = Ca, Ni

Single crystals of hydrated vanadium oxides with layered structures containing divalent Ca or Ni were hydrothermally grown, and their structural characterization was focused on the interlayer sites, Both compounds are formulated by M0.25V2O5 . H2O, M = Ca, Ni and crystallize in the monoclinic system C2/m with Z = 4: a = 11.692(2), b = 3.564(1), c = 10.986(2) Angstrom, b = 105.42(1)degrees for M = Ca; a = 11.756(1), b = 3.649(1), c = 10.364(2) Angstrom, beta = 95.03(1)degrees for M = Ni, The structures consist of delta-type V2O5 layers stacking along the c axis and interlayer hydrated M2+ ions; the delta refers to the V2O5 layer of delta-Ag0.68V2O5 after which the compounds are designated delta-M0.25V2O5 . H2O. The M atoms partially occupy interlayer sites of the 2c position for M = Ni and the 4i position for M = Ca, to each of which four water molecules (O-w) are attached forming MOw4 rectangles, M and O-w site occupancies indicate that the MOw4 rectangles are distributed so that they do not interact with each other, and the above stoichiometric formula correspond to the maximum occupancies, Bonding to three apical oxygens of the V2O5 layers, the Ca atom forms a CaO7 polyhedron, and to two apical oxygens the Ni atom forms a NiO6 octahedron, due to the Ca2+ ion being larger than that of Ni2+ ion, This is the first single-crystal study on the structures of hydrated delta-type vanadium oxide bronzes, (C) 1997 Academic Press.