Syntheses, characterization, and X-ray crystal structures of mono-lacunary Dawson polyoxometalate-based organosilyl complexes

The syntheses and crystal structures of a series of organosilyl polyoxotungstate derivatives with the Dawson monovacant phosphotungstate [alpha(2)-P2W17O61](10-) are described. The polyoxometalates (Me2NH2)(5)H[alpha(2)-P2W17O61{O[Si(CH2)(3)SH](2)}center dot 6H(2)O (Me2NH2-1), (Me2NH2)(6)[alpha(2)-P2W17O61{O[Si(CH2)(3)-SCN](2)}]center dot 3H(2)O (Me2NH2-2), and (Me2NH2)(6)[alpha(2)-P2W17O61-{O(SiPh)(2)}]center dot 4H(2)O (Me2NH2-3) were obtained as analytically pure, homogeneous yellow crystals by the reaction of monolacunary Dawson polyoxotungstate with HS(CH2)(3)Si(OMe)(3), NCS(CH2)(3)Si(OEt)(3), and PhSiCl3, respectively, in an HCl/water/acetonitrile mixed solution or a water/acetonitrile mixed solution, followed by crystallization from water in the dark. Single-crystal X-ray structure analyses revealed that the four-coordinate -Si-O-Si- bonding of the organosilyl groups {O[Si(CH2)(3)SH](2)}, {O[Si(CH2)(3)SCN](2)), and {O(SiPh)(2)} is attained through four oxygen atoms in the mono-lacunary site of the polyanion, resulting in an overall C-1 symmetry for Me2NH2-1 and Me2NH2-2 and C-s symmetry for Me2NH2-3. In the molecular structures of Me2NH2-1 and Me2NH2-2, a unique configuration of the organosilyl groups is observed in the solid state, i.e. the equatorial and axial bonding of each of the two HS(CH2)Si moieties in the {O[Si(CH2)(3)SH](2)} group for Me2NH2-1 and the two NCS(CH2)(3)Si moieties oriented in a syn fashion in the {O[Si(CH2)(3)SCN](2)} group for Me2NH2-2. The characterization of Me2NH2-(1-3) was accomplished by elemental analysis, TG/DTA, and FT-IR, solution (H-1, C-13, and P-31) NNIR, and solid-state C-13 NMR spectroscopy. (c) Wiley-VCH Verlag GmbH & Co.