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

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−, with 2/m symmetry, held together by two pairs μ3-O—H⋯μ1-O and one disordered μ3-O⋯H⋯μ3-O hydrogen bonds.


Structural commentary
While the structure of the dimeric polyanions is clear, the disorder among the potassium atoms and water molecules makes it difficult to be as certain of the chemical structure in the regions in between. The K1-K3 ions were located in special positions, one on a mirror plane and two on twofold rotation axes. The calculated BVSs for the K1-K3 ions are 1.00, 0.90 and 1.00 v.u. (K + Á Á ÁO distance h 3.00 Å ), respec- Polyhedral view of the heteropolyanion in the title compound with O-HÁ Á ÁO contacts of the interanion hydrogen bonds shown as red dashed lines. [Symmetry codes: (i) x, À y + 1, À z + 1; (ii) À x + 1, y, z; (iii) À x + 1, À y + 1, À z + 1.]

Supramolecular features
The polyanion dimers are three-dimensionally linked only via KÁ Á ÁOB, C and T interactions. Water molecules O1W, O2W and O5W do not contribute to the hydrogen bonds.

Synthesis and crystallization
Crystals of the title compound were prepared by the reaction of K 2 MoO 4 Á2H 2 O and K 2 Pt(OH) 6 at pH = ca 6.0. as described in a previous report (Joo et al., 1994).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Atoms H1 and H3 in the polyanion were located in difference Fourier maps and refined with U iso (H) = 1.5U eq (O), and a distance restraint of O-H = 1.00 (3) Å using the DFIX command in SHELXL2014/7 (Sheldrick, 2015). The occupancy of atom H1 was reduced to 0.5 because of disorder. Reasonable displacement parameters for atoms K4-K6 and water molecules O2W-O5W were obtained by reducing their site occupancies to 0.5 because of disorder. The occupancy of K6 was further reduced to 0.25 for charge balance and reasonable displacement parameters. All H atoms of water molecules O1W-O4W were found in difference Fourier maps and refined with distance and angle restraints of O-H = 0.85 (3) Å and HA-OW-HB = 1.35 (3) Å , respectively, using the command DFIX, and were included in the refinement with U iso (H) = 1.5U eq (O). The H atoms on O5W were positioned geometrically and refined using a riding model (HFIX 23), with OW-H = 0.97 Å and U iso (H) = 1.5U eq (O).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.