Redetermination of heptapotassium nonahydrogen bis[α-hexamolybdoplatinate(IV)] undecahydrate

Previously reported at a temperature of 298 (2) K [Lee & Joo (2007 ▶). Acta Cryst. E63, i11–i13], the title compound, K7[H9α-Pt2Mo12O48]·11H2O or K7[H4.5α-PtMo6O24]2·11H2O, was redetermined at 146 (2) K in order to determine whether the H atom in the hydrogen bond that crosses the center of symmetry was located at the center of symmetry or disordered around it as assumed in the previous study. During the present low-temperature study it was found on the center of symmetry. One water molecule shows half-occupancy.

Previously reported at a temperature of 298 (2) K [Lee & Joo (2007). Acta Cryst. E63, i11-i13], the title compound, K 7 [H 9 -Pt 2 Mo 12 O 48 ]Á11H 2 O or K 7 [H 4.5 -PtMo 6 O 24 ] 2 Á11H 2 O, was redetermined at 146 (2) K in order to determine whether the H atom in the hydrogen bond that crosses the center of symmetry was located at the center of symmetry or disordered around it as assumed in the previous study. During the present low-temperature study it was found on the center of symmetry. One water molecule shows half-occupancy.
This study was carried out to identify the position of the hydrogen atom that lies close to the center of symmetry. The structure of the title compound has been discussed in detail (Lee & Joo, 2007).  Table 1). Fig. 2 shows a symmetrical electron density map around H6 atom. The position of H6 is (1/2, 0, 1/2). The distance of O6c-H6 and O6c···.O6c i are 1.28Å and 2.553 (5) Å, and the bond angle of O6c-H6-O6c i is 180 ° (Table 1 & Fig. 3).
The position of H6 was not found on the diffenence map in the previoius report (Lee & Joo, 2007). Therefore the H atom was considered as having positional disorder. The K2 ion is located on the inversion center. As a result the number of K + ion is 7 and H + ion is 9 in the unit cell.

Experimental
Crystals of title compound were prepared by the reaction of K 2 MoO 4 .2H 2 O and K 2 Pt(OH) 6 at pH 2.85 as described in a previous report (Lee & Sasaki, 1994).

Refinement
All H atoms in the polyanion were positioned in a difference Fourier maps and refined freely except H2 and H3. H2 and H3  Fig. 1. The polyanion structure in the title compound. Displacement ellipsoids are drawn at the 50 % probability level for non-H atoms. H atoms are presented as a small spheres of arbitrary radius.

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.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.