Crystal structure of undeca­potassium bis­[α-hemi­penta­hydrogen hexa­molybdoplatinate(IV)] dodeca­hydrate

The title compound, K(11)[α-Pt(μ(3)-OH)(2)(μ(3)-OH(0.5))Mo(6)(μ(3)-O)(3)(μ(2)-O)(6)O(12)](2)·12H(2)O (simplified chemical formula K(11)[H(2.5)PtMo(6)O(24)](2)·12H(2)O), containing the well-known Anderson-type heteropolyoxomolybdate anion, was obtained by hydro­thermal 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 inter­polyanion hydrogen bonds, bond-length elongation and bond-valence sums (BVSs). The title heteropolyanion has two types of protonated O atoms viz. μ(3)-OH, {Mo(2)–O(H)–Pt} and μ(3)-OH(0.5) (disordered H atom). The [H(2.5)α-PtMo(6)O(24)](5.5−) polyanion forms a dimer, [(H(2.5)α-PtMo(6)O(24))(2)](11−), held together by two pairs of μ(3)-O—H⋯μ(1)-O and of one disordered μ(3)-O⋯H⋯μ(3)-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.