Synchrotron structure determination of an alpha-Keggin doubly PtIV-substituted silicotungstate, (CH6N3)8[alpha-SiPt2W10O40].6H2O.

The crystal structure of octaguanidinium alpha-silicodiplatinodecatungstate hexahydrate, (CH(6)N(3))(8)[alpha-SiPt(2)W(10)O(40)].6H(2)O, has been analyzed via a high-energy X-ray diffraction experiment at the SPring-8 BL04B2 beamline. The title compound contains a novel alpha-Keggin heteropolyanion in which two of the addenda atoms are replaced by Pt atoms. W and Pt atoms occupy the same coordinates; the occupancy fractions are 5/6 (W) and 1/6 (Pt), and the alpha-Keggin anion has -4 symmetry. The two types of W(Pt)-W(Pt) distance are in the ranges 3.3565 (4)-3.3704 (4) and 3.7033 (4)-3.7100 (4) A, the four types of W(Pt)-O bond length are in the ranges 1.721 (5)-1.725 (5), 1.910 (5)-1.932 (5), 1.934 (5)-1.956 (5) and 2.339 (4)-2.348 (4) A, and the Si-O bond length is 1.646 (4) A.