Abstract
The reaction of [Ru(arene)Cl-2](2) (arene = benzene, p-cymene) with [X2W22O74(OH)(2)](12-) (X = Sb-III, Bi-III) in buffer medium resulted in four organo-ruthenium supported heteropolytungstates, [Sb2W20O70(RuC6H6)(2)](10-) (1), [Bi2W20O70(RuC6H6)(2)](10-) (2), [Sb2W20O70(RuC10H14)(2)](10-) (3), and [Bi2W20O70(RuC10H14)2](10-) (4), which have been characterized in solution by multinuclear (W-183, C-13, H-1) NMR, UV-vis spectroscopy, electrochemistry, and in the solid state by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis. Polyanions 1, 2, and 4 crystallize in the triclinic system, space group P (l) over bar with the following unit cell parameters: K5Na5[Sb2W20O70(RuC6H6)(2)]center dot 22H(2)O(KNa-1), a = 12.1625(2) angstrom, b = 13.1677(2) angstrom, c = 16.0141(3) angstrom, alpha = 78.9201(7)degrees, beta = 74.4442(8)degrees, gamma = 78.9019(8)degrees, and Z = 1; Cs2Na8[Bi2W20O70(RuC6H6)(2)]center dot 30H(2)O (CsNa-2), a = 11.6353(7) angstrom, b = 13.3638(7) angstrom, c = 16.7067(8) angstrom, alpha = 79.56 (2)degrees, beta = 71.103(2)degrees, gamma = 80.331(2)degrees, and Z = 1; Na-10[Bi2W20O70(RuC10H14)(2)]center dot 35H(2)O (Na-4), a = 15.7376(12) angstrom, b = 15.9806(13) angstrom, c = 24.2909(19) angstrom, alpha = 92.109(4)degrees, beta = 101.354(4)degrees, gamma = 97.365(3)degrees, and Z = 2. Polyanions 1-4 consist of two (L)Ru2+ (L = benzene or p-cymene) units linked to a [X2W20O70](14-) (X = Sb-III, Bi-III) fragment via Ru-O(W) bonds resulting in an assembly with idealized C-2h symmetry. Polyanions 1-4 are stable in solution as indicated by the expected W-183, C-13, and H-1 NMR spectra. The electrochemistry of 1-4 is described by considering the reduction and the oxidation processes. The nature of the arene in Ru(arene) has practically no influence on the formal potentials of the W-centers, which are more sensitive to the Sb or Bi hetero atoms. The results suggest that the respective Sb- and Bi derivatives have very different pK(a) values, with the reduced form of 1 being the most basic, thus permitting the observation of two Well-developed voltammetric waves at pH 6. In contrast, the identity of the arene influences the oxidation processes, thus permitting to distinguish them. A strong electrocatalytic water oxidation peak is observed that is more positive than the one corresponding to the Ru(arene) oxidation process. Also a stepwise oxidation of the Ru(benzene) group could be observed at pH 3. The catalytic efficiency, on the other hand, of 1-4 toward the oxidation of n-hexadecane and p-xylene illustrated the effect of ruthenium substitution on the polyanion catalytic performance.