Crystal structure of undeca-potassium bis-[α-hemi-penta-hydrogen hexa-molybdoplatinate(IV)] dodeca-hydrate.

The title compound, K11[α-Pt(μ3-OH)2(μ3-OH0.5)Mo6(μ3-O)3(μ2-O)6O12]2·12H2O (simplified chemical formula K11[H2.5PtMo6O24]2·12H2O), containing the well-known Anderson-type heteropolyoxomolybdate anion, was obtained by hydro-thermal reaction at pH = ca 6.0. The complete polyanion dimer has 2/m symmetry. The locations of the H atoms with respect to protonated O atoms were obtained from difference Fourier maps, and confirmed by the inter-polyanion hydrogen bonds, bond-length elongation and bond-valence sums (BVSs). The title heteropolyanion has two types of protonated O atoms viz. μ3-OH, {Mo2-O(H)-Pt} and μ3-OH0.5 (disordered H atom). The [H2.5α-PtMo6O24](5.5-) polyanion forms a dimer, [(H2.5α-PtMo6O24)2](11-), held together by two pairs of μ3-O-H⋯μ1-O and of one disordered μ3-O⋯H⋯μ3-O hydrogen bonds. Three K(+) ions are located on special positions (two on twofold rotation axes, one on a mirror plane), and two K(+) ions are located on general positions with a reduced occupancy of 0.5. The remaining K(+) ion has a reduced occupancy of 0.25 for charge balance and reasonable displacement parameters. As a result, the numbers of K(+) and H(+) ions in the title compound are 5.5 and 2.5, respectively.