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The synthesis, electrochemistry, and magnetism of two novel dimeric, [Fe.sup.3}-containing tungstogermanates is reported. Both polyanions exhibit diamagnetic ground states with a small amount of paramagnetic impurity and have common simultaneous reduction of all of their [Fe.sup.3} centers.

The benzene-Ru(II)-supported dilacunary decatungstosilicate [{Ru(C6H6)(H2O)}{RU(C6H6)}(gamma-SiW10(O36)).sup.4-] (1)and the isostructural decatungstogermanate [{Ru(C5H5)(H2O)}{RU(C6H6)}(gamma-SiW10(O36)).sup.4-] (2) are synthesized and characterized by multinuclear solution NMR, IR, elemental analysis, and electrochemistry. A ligand substitution reaction was observed upon addition of dimethyl sulfoxide (dmso) to 1,2, or [Ru(C6H6)Cl2.sub.2], which facilitates substantially the oxidation of the Ru center.

Electronic structure methods are used for studying the transition state and products of the reaction between alkyl radicals and CO coordinated in transition-metal complexes. The results have helped in understanding the mechanism of photochemical alkane carbonylation systems by using [d.sup.8]-M[L.sub.5] metal carbonyls as cocatalysts.

The dilacunary decatungstogermanate, {[gamma]-Ge[W.sub.10][O.sub.36]}[.sup.8-] is synthesized and structurally characterized in solution and in the solid state. Polyanion {[gamma]-Ge[W.sub.10][O.sub.36]}[.sup.8-] represents a novel lacunary polyoxometalate, giving rise to a multitude of derivatives by reaction with transition metals, lanthanides and other electrophiles.

A family of {Ru(arene)}2+-containing heteropolytungstates of general formula [{Ru(L)}2(α-XW11O39)2WO2] m- (L = benzene, p-cymene; X = GeIV, SiIV, m = 10; X = BIII, m = 12) has been prepared in aqueous acidic medium (pH ≈ 4). The 1:1 interaction of [Ru(C6H6)Cl2]2 or [Ru( p-cymene)Cl2]2 with [β2-GeW11O39]8- led to the formation of [{Ru(benzene)}2(GeW11O39)2WO2]10- ( 1) and [{Ru( p-cymene)}2(GeW11O39)2WO2]10- ( 2), respectively. Replacing [β2-GeW11O39]8- by [α-SiW11O39]8- resulted in [{Ru(benzene)}2(SiW11O39)2WO2]10- ( 3) and [{Ru( p-cymene)}2(SiW11O39)2WO2][SiW12O40]0.512- ( 4), respectively. The reaction of [α-HBW11O39]8- with the respective {Ru(arene)}2+-containing precursors resulted in polyanions [{Ru(benzene)}2(HBW11O39)2WO2]10- ( 5) and [{Ru( p-cymene)}2(HBW11O39)2WO2]10- ( 6), respectively. Single-crystal XRD analysis of the hydrated salts of 1- 6 revealed that these species comprise two Keggin fragments, [{Ru(L)}α-XW11O39]6- (L = benzene, p-cymene; X = GeIV, SiIV) for polyanions 1- 4 and [{Ru(L)}α-HBW11O39]6- (L = benzene, p-cymene) for 5 and 6, connected via a cis-dioxo {WO2}2+ unit. In addition, the heteropolytungstates were characterized by thermogravimetric analysis, IR spectroscopy, elemental analysis, and solution electrochemical studies. [ABSTRACT FROM AUTHOR]

Electronic structure methods have been used to study the transition state and products of the reaction between alkyl radicals and CO coordinated in transition-metal complexes. At the B3LYP DFT level, methyl addition to a carbonyl of [Ru(CO)5] or [Ru(CO)3(dmpe)] is calculated to be about 6 kcal/mol more exothermic than addition to free CO. In contrast, methyl addition to [Mo(CO)6] is 12 kcal/mol less exothermic than addition to CO, while the reaction enthalpy of methyl addition to [Pd(CO)4] is comparable to that of free CO. Related results are obtained at the CCSD-T level and for the reactions of the cyclohexyl radical. The transition state for these reactions is characterized by significant distortion of the geometry of the reactant complex, which include lengthening and bending of the M-CO bond, but with negligible C-C bond formation. Accordingly, the activation energy for addition to coordinated carbonyls is 2-10 kcal/mol greater than that of addition to free CO. Additional calculations were also carried out on representative unsaturated metal carbonyls. The calculated results afford an understanding of the mechanism of previously reported photochemical alkane carbonylation systems utilizing d8-ML5 metal carbonyls as cocatalysts. In particular, it is strongly indicated that such systems operate via direct attack by an alkyl radical at a CO ligand, a reaction that has not previously been proposed. [ABSTRACT FROM AUTHOR]

Interaction of the dilacunary polyanion precursor [γ-GeW10O36]8- with Fe3+ ions in aqueous buffer medium (pH 4.8) results in the formation of two dimeric tungstogermanates depending on the reactant ratios. When using an Fe3+ to [γ-GeW10O36]8- ratio of 1:1, the asymmetric anion [K(H2O)(β-Fe2GeW10O37(OH))(γGeW10O36)]12- (1) is formed, whereas [{β-Fe2GeW10O37(OH)2}2]12- (2) is formed when using a ratio of 2:1. Single-crystal X-ray analyses were carried out on Cs3K9[K(H2O)(β-Fe2GeW10O37(OH))(γ-GeW10O36)]·19H2O (CsK-1), which crystallizes in the triclinic system, space group P1, a = 11.4547(2), b = 19.9181(5), c = 21.0781(6) Å, α = 66.7977(12), β 89.1061(12), γ = 84.4457(11)°, and Z = 2 and on Cs7K4Na[{β-Fe2GeW10O37(OH)2}2]—39H2O (CsKNa-2), which crystallizes in the monoclinic system, space group C2/m, a = 32.7569(13), b = 12.2631 (5), c= 14.2895(5) Å, β = 104.135(2)°, and Z= 2. Polyanion 1 consists of (β-Fe2GeW10O37) and (γ-GeW10O36) units linked via two Fe—O—W bridges and a central potassium ion. Two equivalent FeO6 octahedra complete the belt of the β-Keggin unit and link to the (γ-GeW10O36) fragment. On the other hand, 2 consists of two {β-Fe2GeW10O37(OH)2} units with four bridging hydroxo groups linking the four Fe3+ ions, forming an eight-membered ring. The magnetic properties of CsK-1 and CsKNa-2 have been studied by magnetic susceptibility and magnetization measurements and fitted according to an isotropic exchange model. Both polyanions 1 and 2 exhibit diamagnetic ground states with a small amount of paramagnetic impurity. Electrochemistry studies on 1 and 2 were carried out in a pH 5 acetate medium. The two polyanions have in common the simultaneous reduction of all of their Fe3+ centers. This observation suggests the existence of identical or almost-identical influences on these centers and their equivalence, especially in the reduced state. Controlled potential coulometry results indicate the presence of two Fe3+ centers in 1 and four in 2. The splitting of the tungsten wave of 1 compared to the single tungsten wave of 2 is attributed to a difference in acid—base properties of the polyanions. Voltammetric peak-potential shifts as a function of pH were studied in the case of 2. [ABSTRACT FROM AUTHOR]

The dilacunary decatungstogermanate [γ-GeW10O36]8- (1) has been synthesized and structurally characterized in solution and in the solid state. Reaction of germanium dioxide with sodium tungstate in aqueous acidic medium results in the formation of [β2-GeW11O39]8- (2), which is then used as a precursor for the synthesis of 1. The 183W spectrum of 2 shows the expected 11 peaks of equal intensity, whereas that of 1 exhibits the expected three peaks with relative intensities 2:2:1. Polyanion 1 represents a novel lacunary polyoxometalate, giving rise to a multitude of derivatives by reaction with transition metals, lanthanides, and other electrophiles. [ABSTRACT FROM AUTHOR]

At variance with previously known coordination compounds, the polyoxometalate (POM)-embedded Zr(IV) and Hf(IV) peroxides with formula: [M(2)(O(2))(2)(α-XW(11)O(39))(2)](12-) (M=Zr(IV), X=Si (1), Ge (2); M=Hf(IV), X=Si (3)) and [M(6)(O(2))(6)(OH)(6)(γ-SiW(10)O(36))(3)](18-) (M=Zr(IV) (4) or Hf(IV) (5)) are capable of oxygen transfer to suitable acceptors including sulfides and sulfoxides in water. Combined (1)H NMR and electrochemical studies allow monitoring of the reaction under both stoichiometric and catalytic conditions. The reactivity of peroxo-POMs 1-5 is compared on the basis of substrate conversion and kinetic. The results show that the reactivity of POMs 1-3 outperforms that of the trimeric derivatives 4 and 5 by two orders of magnitude. Reversible peroxidation of 1-3 occurs by H(2)O(2) addition to the spent catalysts, restoring oxidation rates and performance of the pristine system. The stability of 1-3 under catalytic regime has been confirmed by FT-IR, UV/Vis, and resonance Raman spectroscopy. The reaction scope has been extended to alcohols, leading to the corresponding carbonyl compounds with yields up to 99% under microwave (MW) irradiation. DFT calculations revealed that polyanions 1-3 have high-energy peroxo HOMOs, and a remarkable electron density localized on the peroxo sites as indicated by the calculated map of the electrostatic potential (MEP). This evidence suggests that the overall description of the oxygen-transfer mechanism should include possible protonation equilibria in water, favored for peroxo-POMs 1-3., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)