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Michael H Dickman

Publications and source records attributed to Michael H Dickman.

12 recordsLinked to original sources
PubMed2006

A novel hexatungstate fragment stabilized by dimethyltin groups: [{(CH3)2Sn}2(W6O22)]4-.

Reaction of Na2WO4 and (CH3)2SnCl2 in water (pH 7) led to the formation of the hybrid organic-inorganic polyanion [{(CH3)2Sn}2(W6O22)]4- (1), which is composed of a novel hexatungstate core stabilized by two dimethyltin groups. Selective crystallization of 1 with guanidinium cations resulted in [C(NH2)3]4[{CH3)2Sn}2(W6O22)]2H2O (1a), which exhibits a 1D arrangement via distorted trigonal-bipyramidal cis-(CH3)2SnO3 moieties.

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PubMed2006

Hybrid organic-inorganic assemblies based on molybdates and dimethyltin linkers.

Reaction of (CH3)2SnCl2 with Na2MoO4 in an aqueous medium results in three different compounds depending on the pH: [{(CH3)2Sn}(MoO4)] (1), [{(CH3)2Sn}4O2(MoO4)2] (2), and [{(CH3)2Sn}{Mo2O7(H2O)2}].H2O (3). All three species have been characterized in the solid state by means of elemental analysis, infrared spectroscopy, thermogravimetry, and single-crystal X-ray diffraction. Compounds 1-3 all show hybrid organic-inorganic extended lattices based on molybdate anions linked by (CH3)2Sn2+ moieties, and the coordination numbers of the Sn(IV) centers range from 5 to 7. Compound 1 crystallizes in the orthorhombic space group Pnma with cell parameters a = 13.2035(4) A, b = 7.2634(2) A, c = 7.1458(2) A, and Z = 4. 1 exhibits a complex, 3-dimensional network structure constructed of corner-shared, tetrahedral orthomolybdate oxoanions and distorted octahedral trans-(CH3)2SnO4 groups. Compound 2 crystallizes in the monoclinic space group P2(1)/n with cell parameters a = 8.2330(1) A, b = 11.4033(2) A, c = 12.1529(2) A, beta = 91.566(1) degrees , and Z = 2. Its 2-dimensional layered structure contains dimeric tetramethyldistannoxane [{(CH3)2Sn}4O2]2+ subunits built up of edge-sharing cis-(CH3)2SnO4 distorted trigonal bipyramids and connected in the (1,0,) plane by tetrahedral orthomolybdate oxoanions, the layers packing along the crystallographic a axis with the methyl groups pointing to the interlamellar space. Compound 3 crystallizes in the orthorhombic space group Pbcm with cell parameters a = 6.5594(4) A, b = 14.2465(11) A, c = 11.3892(8) A, and Z = 4. It shows dimeric [Mo2O8(H2O)2] units sharing corners to form zigzagging polymeric {[Mo2O7(H2O)2]2-}infinity polyanions along the [001] direction; these chains are further linked by trans-(CH3)2SnO5 distorted pentagonal bipyramids to give layers parallel to the (010) plane, the interlamellar space being occupied by hydrogen-bonded hydration water molecules.

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PubMed2006

Dilacunary decatungstates functionalized by organometallic ruthenium(II), [{Ru(C6H6)(H2O)}{Ru(C6H6)}(gamma-XW10O36)]4- (X = Si, Ge).

The benzene-Ru(II)-supported dilacunary decatungstosilicate [{Ru(C6H6)(H2O)}{Ru(C6H6)}(gamma-SiW10O36)]4- and the isostructural decatungstogermanate [{Ru(C6H6)(H2O)}{Ru(C6H6)}(gamma-GeW10O36)]4- have been synthesized and characterized by multinuclear solution NMR, IR, elemental analysis, and electrochemistry. Single-crystal X-ray analysis was carried out on K4[{Ru(C6H6)(H2O)}{Ru(C6H6)}(gamma-SiW10O36)].9H2O (K-1), which crystallizes in the orthorhombic system, space group Pmn2(1), with a = 13.6702(3) A, b = 16.2419(4) A, c = 12.1397(2) A, and Z = 2, and on K4[{Ru(C6H6)(H2O)}{Ru(C6H6)}(gamma-GeW10O36)].7H2O (K-2), which also crystallizes in the orthorhombic system, space group Pmn2(1), with a = 13.6684(12) A, b = 16.297(2) A, c = 12.1607(13) A, and Z = 2. Polyanions 1 and 2 consist of a Ru(C6H6)(H2O) group and a Ru(C6H6) group linked to a dilacunary (gamma-XW10O36) Keggin fragment resulting in an assembly with idealized Cs symmetry. The Ru(C6H6)(H2O) group is bound at the lacunary polyanion site via two Ru-O(W) bonds, whereas the Ru(C6H6) group is bound on the side via three Ru-O(W) bonds. Polyanions 1 and 2 were synthesized in aqueous acidic medium at pH 2.5 by the reaction of [Ru(C6H6)Cl2]2 with [gamma-SiW10O36]8- and [gamma-GeW10O36]8-, respectively. The formal potentials are roughly the same for the first W waves of 1 and 2. However, important differences appear for the second W waves. These observations indicate different acid-base properties for the reduced forms of 1 and 2. Three oxidation processes were detected: the oxidation of the Ru center is followed first by irreversible electrocatalytic processes of the Ru-benzene moiety and then of the electrolyte. Comparison of this behavior with that of the precursor reagent, [Ru(C6H6)Cl2]2, was useful to understand the main oxidation processes. A ligand substitution reaction was observed upon addition of dimethyl sulfoxide (dmso) to 1, 2, or [Ru(C6H6)Cl2]2. This reaction facilitates substantially the oxidation of the Ru center. The dmso was oxidized with large electrocatalytic currents more efficiently in the presence of 1 and 2 than with [Ru(C6H6)Cl2]2.

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PubMed2006

Transition metal containing decatungstosilicate dimer [M(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (M = Mn(2+), Co(2+), Ni(2+)).

The new, monometal substituted silicotungstates [Mn(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (1), [Co(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (2) and [Ni(H(2)O)(2)(gamma-SiW(10)O(35))(2)](10-) (3) have been synthesized and isolated as the potassium salts K(10)[Mn(H(2)O)(2)(gamma-SiW(10)O(35))(2)] x 8.25 H(2)O (K-1), K(10)[Co(H(2)O0(2)(gamma-SiW(10)O(35))(2)] x 8.25 H(2)O (K-2) and K(10)[Ni(H(2)O)(2)(gamma-SiW(10)O(35))(2)] x 13.5 H(2)O (K-3), which have been characterized by IR spectroscopy, single crystal X-ray diffraction, elemental analysis and cyclic voltammetry. Polyanions 1-3 are composed of two (gamma-SiW(10)O(36)) units fused on one side via two W-O-W' bridges and on the other side by an octahedrally coordinated trans-MO(4)(OH(2))(2) transition metal fragment, resulting in a structure with C(2v) point group symmetry. Anions 1-3 were synthesized by reaction of the dilacunary precursor [gamma-SiW(10)O(36)](8-) with Mn(2+), Co(2+) and Ni(2+) ions, respectively, in 1 M KCl solution at pH 4.5. The electrochemical properties of 1-3 were studied by cyclic voltammetry and controlled potential coulometry in a pH 5 buffer medium. The waves associated with the W-centers are compared with each other and with those of the parent lacunary precursor [gamma-SiW(10)O(36)](8-) in the same medium. They appear to be dominated by the acid-base properties of the intermediate reduced species. A facile merging of the waves for 3 is observed while those for 1 and 2 remain split. Controlled potential coulometry of the single wave of 3 or the combined waves of 1 and 2 is accompanied by catalysis of the hydrogen evolution reaction. No redox activity was detected for the Ni(2+) center in 3, whereas the Co(2+) center in 2 shows a one-electron redox process. The two-electron, chemically reversible process of the Mn(2+) center in 1 is accompanied by a film deposition on the electrode surface.

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PubMed2006

Structural characterization of mono-ruthenium substituted Keggin-type silicotungstates.

We have synthesized the mono-ruthenium substituted Keggin-type silicotungstate [SiW(11)O(39)Ru(III)(H(2)O)](5-) (1a) by reaction of the mono-lacunary silicotungstate precursor [SiW(11)O(39)](8-) with Ru(acac)(3) under hydrothermal conditions and isolated as the caesium salt Cs(5)[SiW(11)O(39)Ru(III)(H(2)O)] (1). The DMSO-coordinated complex [SiW(11)O(39)Ru(III)(DMSO)](5-) (2a) was prepared by reaction of 1a with DMSO in aqueous solution at 353 K and isolated as the caesium-potassium mixed salt Cs(4.9)K(0.1)[SiW(11)O(39)Ru(III)(DMSO)] (2). Both compounds 1 and 2 were characterized by single-crystal X-ray structure analysis, powder X-ray structure analysis, UV-Vis spectroscopy, cyclic voltammetry, IR-spectroscopy and elemental analysis. 1 crystallized in the tetragonal space group P4(2)/ncm with a = 20.9299(4), c = 10.3603(4) Angstrom, Z = 4. The ruthenium atom in the Keggin unit could not be distinguished from the tungsten due to disorder. The structural analysis of 2 (monoclinic, P2(1)/c, a = 13.5850(4), b = 20.2764(7), c = 18.1326(4) Angstrom, beta = 90.8730(10) degrees , Z = 4) successfully revealed that the incorporated ruthenium atom is coordinated by DMSO through a Ru-S bond. Polyanion 2a represents the first mono-substituted Keggin ion in which the ruthenium center is not crystallographically disordered. UV-Vis spectroscopy combined with controlled potential electrolysis confirmed that the incorporated rutheniums in 1 and 2 have a valence state of +3. The IR spectra of both 1 and 2 were very similar. All these data indicate that 1 synthesized by reaction of the mono-lacunary silicotungstate K(8)[SiW(11)O(39)] with Ru(acac)(3) under hydrothermal conditions is truly the mono-ruthenium substituted Keggin-type silicotungstate.

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PubMed2006

Synthesis and structure of dilacunary decatungstogermanate, [gamma-GeW10O36]8-.

The dilacunary decatungstogermanate [gamma-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 [beta2-GeW11O39]8- (2), which is then used as a precursor for the synthesis of 1. The (183)W 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.

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PubMed2006

Synthesis and structure of asymmetric zirconium-substituted silicotungstates, [Zr6O2(OH)4(H2O)3(beta-SiW10O37)3]14- and [Zr4O2(OH)2(H2O)4(beta-SiW10O37)2]10-.

The reaction of ZrCl4 with [gamma-SiW10O36]8- in a potassium acetate buffer results in two different products depending on the reactant ratios. The trimeric species [Zr6O2(OH)4(H2O)3(beta-SiW10O37)3]14- (1) consists of three beta23-SiW10O37 units linked by an unprecedented Zr6O2(OH)4(H2O)3 cluster with C1 point group symmetry. The dimeric species [Zr4O2(OH)2(H2O)4(beta-SiW10O37)2]10- (2) consists of beta22- and beta12-SiW10O37 units sandwiching a Zr4O2(OH)2(H2O)4 cluster, which also has C1 symmetry. Polyanion 1 contains more zirconium centers than any other polyoxometalate known to date.

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PubMed2005

Trilacunary heteropolytungstates functionalized by organometallic ruthenium(II), [(RuC6H6)2XW9O34]6- (X = Si, Ge).

The benzene-Ru(II)-supported trilacunary heteropolytungstates [(RuC6H6)2XW9O34]6- (X = Si, 1; Ge, 2) have been synthesized and characterized by multinuclear solution NMR (183W, 13C, 1H, 29Si), UV-vis and IR spectroscopy, electrochemistry, and elemental analysis. Single-crystal X-ray analysis was carried out on Rb2Na4[(RuC6H6)2SiW9O34].21H2O (RbNa-1), which crystallizes in the triclinic system, space group P, with a = 11.9415(2) A, b = 13.3123(2) A, c = 19.4927(4) A, alpha = 96.6460(10) degrees , beta = 95.1570(10) degrees , gamma = 98.2560(10) degrees , and Z = 2 and on Cs2Na4[(RuC6H6)2GeW9O34].19.5H2O (CsNa-2), which crystallizes also in the triclinic system, space group P, with a = 11.930(4) A, b = 13.353(4) A, c = 19.586(6) A, alpha = 95.982(5) degrees , beta = 95.414(6) degrees , gamma = 98.142(5) degrees , and Z = 2. The novel polyanion structure consists of two (RuC6H6) units linked to a trilacunary (XW9O34) Keggin fragment via Ru-O(W) and Ru-O(X) bonds resulting in an assembly with Cs symmetry. Polyanions 1 and 2 were synthesized by reaction of [RuC6H6Cl2]2 with [A-alpha-XW9O34]10- in aqueous buffer medium (pH 6.0). Both 1 and 2 are stable in solution as indicated by the expected 5-line pattern (2:1:2:2:2) in the 183W NMR and the expected (3C, 1H, and 29Si spectra. Descriptions of the respective electrochemical behaviors of the W centers and the Ru centers in 1 and 2 are given in media where these processes are clearly defined. In a pH = 3 acetate medium, the cyclic voltammetry of the W centers shows the known fingerprint of the trilacunary alpha-[XW9O34]n- (X = Ge, Si) moieties. The presence of the (RuC6H6) substituents imparts a good stability to these fragments in solution. Stepwise oxidation of the Ru centers was suspected in pH = 5 acetate medium, but only the first step was well-separated from a large current composite wave. The stepwise oxidation was finally observed clearly in a DMF-water (90/10 v/v) mixture and shows two well-behaved Ru oxidation processes. A short comparison is made with DMSO-bearing Ru polyoxometalates.

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PubMed2005

The Ru(II)-supported heptatungstates [HXW7O28Ru(dmso)3]6-(X=P, As).

The ruthenium(II)-supported heteropolyanions [HXW7O28Ru(dmso)3]6-(X=P, 1; As, 2) are composed of a Ru(dmso)3 group attached to an unprecedented heptatungstate fragment via two Ru-O-W bonds and one Ru-O-X bond, which represents a fundamentally novel mode of Ru-coordination to a polyoxoanion framework. Multinuclear 183W, 31P, 13C, and 1H NMR studies indicate high stability of 1 and 2 in solution.

Magnetic Resonance Spectroscopy↗
PubMed2005

Confirmation of the semivacant Wells-Dawson polyoxotungstate skeleton. The structures of [Ce{X(H4)W17O61}2]19- (X = P, As) indicate the probable location of internal protons.

Reaction of Ce(III) with lacunary versions of [H(4)XW(18)O(62)](7-) (X = P, As) yields the 1:2 complexes [Ce(H(4)XW(17)O(61)](19-) (X = As, 1; P, 2) in good yield, characterized in solution and the solid state by NMR spectroscopy and X-ray crystallographic analysis, respectively. The structures confirm a syn C(2) conformation that is analogous to that observed for [Ln(alpha(2)-P(2)W(17)O(61))(2)](17-) but with "empty" O(4) tetrahedra that are in positions remote from the cerium atom. Bond valence sum calculations for these structures show that the four protons that are required for charge balance in all salts of the XW(18) anions and their lacunary derivatives are almost certainly bound to the oxygen atoms of the empty tetrahedra.

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