A new mate for vanadate: The platinum(IV)‐containing polyoxovanadate [H2PtIVV9O28]5− (1) has been synthesized and structurally characterized (see polyhedral representation). The characterization of polyanion 1 in solution by 195Pt NMR spectroscopy is unprecedented in POM chemistry. The facile synthetic procedure with the PtIV precursor H2Pt(OH)6 appears to be a convenient and general methodology for making a large variety of PtIV‐containing polyoxometalates.

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.

In Vanadat eingebettet: Das erste Platin(IV)‐haltige Polyoxovanadat, [H2PtIVV9O28]5− (1), wurde synthetisiert und strukturell beschrieben (siehe Polyederdarstellung). Die Anwendung der 195Pt‐NMR‐Spektroskopie zur Charakterisierung von 1 in Lösung ist innerhalb der POM‐Chemie neu. Die simple Synthese mit der Vorstufe H2Pt(OH)6 erscheint als nützliche und allgemeine Methode für die Präparation vielfältiger PtIV‐haltiger Polyoxometallate.

The title compound, K3.5[H4.5α‐PtMo6O24]·5.5H2O, containing the hexa­molybdoplatinate(IV) polyanion, was isolated at pH 2.85. The complete polyanion has no crystallographic symmetry. The [H4.5α‐PtMo6O24]3.5− polyanions form an inversion‐generated dimer, viz. [H9(PtMo6O24)2]7−, via seven strong hydrogen bonds, one of which is disordered. One K+ ion and one water O atom occupy inversion centres.

We report on the feasibility of applying high-resolution solid-state 195 Pt MAS NMR spectroscopy for several Pt IV -containing polyoxotungstates, and of 195 Pt as well as 51 V for a Pt IV -containing polyoxovanadate. This method is particularly useful for polyanions which are unstable in solution and/or poorly soluble, as well as for systems exhibiting crystallographic disorder of Pt and W sites. We also report solution 195 Pt and 183 W NMR spectra of hexatungstoplatinate(IV) [H 3 PtW 6 O 24 ] 5À for the first time.