The structure of tetra-potassium-divanadate-dihydrate

K4V2O7.2H2O, Mr=406.30, orthorhombic, Cmcm, a=11.2156(5), b=12.3711(5), c=8.0751(4) A, V=1120.42(9) A3, Z=4, Dx=2.409 Mg m-3, λ(CuKα1)=1.540562, λ(CuKα2)=1.544390 A for lattice parameters, λ(MoKα)=0.71073 A for intensity measurement, μ=3.12 mm-1, F(000)=792, T=298 K, final R=0.053 for 1022 unique observed reflections. The V2O7 group has an eclipsed conformation with m2m symmetry, the diad axis being parallel to [010], V-O-V 171.4(5)0. The groups are arranged like the lattice points of a face-centred lattice, each being surrounded by four K+ ions within a plane parallel to (001). The K+ ions are coordinated by seven to eleven O atoms including water molecules. (orig.)