The ruthenium(II)-supported heteropolytungstates [Ru(dmso)3(H2O)-XW11O39]6- (X = Ge, Si)

The novel Ru(II)-supported heteropolytungstates [Ru(dmso)(3)(H2O)XW11O39](6-) (X=Ge, Si) have been synthesized and characterized by single-crystal X-ray diffraction, multinuclear NMR (W-183, C-13, H-1, Si-29) and IR spectroscopy, elemental analysis and electrochemistry. The novel polyanion structure consists of a Ru(dmso)(3)(H2O) unit linked to a monolacunary [XW11O39](8-) Keggin fragment via two Ru-O-W bonds resulting in an assembly with C-1 symmetry. Polyanions 1 and 2 were synthesized by reaction of cis-Ru(dmso)(4)Cl-2 with [A-alpha-XW9O34](10-) in aqueous, acidic medium (pH 4.8). Tungsten-183 NMR of 1 leads to a spectrum with 11 peaks of equal intensity, indicating that the solid-state structure is preserved in solution. Electrochemistry studies revealed that 1 and 2 are stable in solution at least from pH 0 to 7, even in the presence of dioxygen. Their cyclic voltammetry patterns show mainly two two-electron reversible W-waves, those of the Si derivative 2 being located at slightly more negative potentials than those of the Ge derivative 1. The observed stability of 1 and 2 might be attributed to a stabilization of the Ru-center both by the strongly bound dmso ligands and the Keggin moiety. This stabilization drives the redox waves of Ru outside the accessible potential range. However, conditions were found to reveal, at least partially, the redox behavior of Ru in 1 and 2.