Biomedical subjects

Timothy Hughbanks

Publications and source records attributed to Timothy Hughbanks.

6 recordsLinked to original sources

PubMed2004

Cyanide-melt synthesis of reduced molybdenum selenide clusters.

The tightly cross-linked Mo(3n)Se(3n+2) (n = 2, 3,... infinity) cluster compounds react with alkali metal cyanide or cyanide salt mixtures at temperatures of 450-675 degrees C to yield cyanide-terminated molybdenum chalcogenide clusters, [Mo6Se8(CN)6]n- (1n-) (n = 6, 7) and [Mo4Se4(CN)12](8-) (2(8-)). The process by which discrete 1(n-) clusters are excised from a CN-linked intermediate chain compound, K6Mo6Se8(CN)5 (3), was investigated, and the cubane cluster 2(7-) plays an essential role. An efficient one-step synthesis for Na8[2(8-)] is presented. These clusters are stable in basic aqueous solutions. Cyclic voltammetric (CV) measurements in basic aqueous media show multiple reversible redox waves corresponding to 1(6-/7-), 1(7-/8-), and 1(8-/9-) redox couples with half-wave potentials of E(1/2) = -0.442, -0.876, and -1.369 V, respectively, versus SHE. Half-wave potentials (E(1/2)) for the [Mo4Se4)(CN)12](6-/7-) and [Mo4Se4(CN)12](7-/8-) couples are 0.233 and -0.422 V, respectively, versus SHE. The 2(8-) compounds are K7Na[2(8-)].5H2O.MeOH, Cs7Na4[2(8-)]Cl3, Na8[2(8-)], and K4Na4[2(8-)].12H2O. The products were characterized by X-ray crystallography, cyclic voltammetry, and UV-vis spectroscopy. Reduction potentials measured by voltammetry are consistent with conditions needed for isolating reduced species on a preparative scale but are much more negative than previously reported values. Na8[1(8-)].20H(2)O was isolated by reduction of 1(7-) with Zn in aqueous NaCN solution. Reduction potentials measured in basic NaCN solutions of 2(8-) also differ widely from previous reported values.

Journal Article↗

PubMed2003

The first framework solid composed of vanadosilicate clusters.

In this Communication, we report the first example of a network structure composed of vanadosilicate clusters. We utilized hydrothermal conditions to synthesize a polyoxovanadogermanate (POVG): (C4H14N2)4[V14O44(GeOH)8].6H2O. By substituting SiO2 for GeO2 in the synthesis, a framework solid, H4V18O46(SiO)8C4H12N2)4.(H2O)] .4H2O, is formed in which isostructural vanadosilicate clusters are linked by five-coordinate vanadium with a (VO)O2N2 environment. The charge-compensating organic amine, 1,4-diaminobutane, in the POVG is covalently bonded to the linking vanadium polyhedra in the framework solid.

Journal Article↗

PubMed2002

N-centered hexazirconium chloride clusters: excision and redox chemistry.

The tightly cross-linked solid Zr(6)Cl(15)N yields [(Zr(6)NCl(12))Cl(6)](3-) upon heating with bis(triphenylphosphine)iminium chloride (PPNCl), in MeCN at 90 degrees C. Purple solutions containing [(Zr(6)NCl(12))Cl(6)](3-) were obtained and characterized with (15)N NMR. Cyclic voltammetric (CV) measurements on the series of [(Zr(6)ZCl(12))Cl(6)](n-) cluster ions (Z = Be, B, C, and N) in acetonitrile reveal that these cluster ions exhibit multiple reversible redox waves at potentials that can be systematically understood, including a reversible redox wave corresponding to the [(Zr(6)NCl(12))Cl(6)](3-/4-) couple. Preparation of the reduced cluster ion, [(Zr(6)NCl(12))Cl(6)](4-), (with 15 cluster-bonding electrons) was achieved by reduction of [(Zr(6)NCl(12))Cl(6)](3-) with (C(5)(CH(3))(5))(2)Co. Several new N-centered cluster complexes: (PPN)(3)[(Zr(6)NCl(12))Cl(6)].CH(2)Cl(2), [(C(5)(CH(3))(5))(2)Co(+)](3)[(Zr(6)NCl(12))Cl(6)], and (Et(4)N)(4)[(Zr(6)NCl(12))Cl(6)].2CH(3)CN have been isolated and structurally characterized.

Journal Article↗

PubMed1999

Electrochemistry of Centered Hexanuclear Zirconium Halide Clusters in Ambient-Temperature Chloroaluminate Molten Salts.

Ambient temperature AlCl(3)-1-ethyl-3-methylimidazolium chloride (ImCl) molten salts, both basic (40/60 mol % AlCl(3)/ImCl) and acidic (60/40 mol % AlCl(3)/ImCl), were used in an electrochemical investigation of centered hexanuclear zirconium halide clusters. In the basic molten salt, these [(Zr(6)ZCl(12))Cl(6)](n-) (Z = Be, B, C, Mn, Fe) centered clusters exhibit the following electrochemical reactions on a glassy carbon electrode (potentials vs Al/Al(3+)): [(Zr(6)BeCl(12))Cl(6)](n)()(-) + e(-) right harpoon over left harpoon [(Zr(6)BeCl(12))Cl(6)](()(n)()(+1))(-), E(1/2) = -0.613 V (n = 4), E(1/2) = -1.085 V (n = 5); [(Zr(6)BCl(12))Cl(6)](n)()(-) + e(-) right harpoon over left harpoon [(Zr(6)BCl(12))Cl(6)](()(n)()(+1))(-), E(1/2) = -0.365 V (n = 4), E(1/2) = 0.072 V (n = 3); [(Zr(6)CCl(12))Cl(6)](n)()(-) + e(-) right harpoon over left harpoon [(Zr(6)CCl(12))Cl(6)](()(n)()(+1))(-), E(1/2) = 0.230 V (n = 3); [(Zr(6)MnCl(12))Cl(6)](4)(-) + e(-) right harpoon over left harpoon [(Zr(6)MnCl(12))Cl(6)](5)(-), E(1/2) = -0.432 V. In the acidic melt, only electrochemical reactions [(Zr(6)BeCl(12))(AlCl(4))(6)](n)()(-) + e(-) right harpoon over left harpoon [(Zr(6)BeCl(12))(AlCl(4))(6)](()(n)()(+1))(-), E(1/2) = -0.069 V (n = 5), E(1/2) = 0.504 V (n = 4), and [(Zr(6)BCl(12))(AlCl(4))(6)](4)(-) + e(-) right harpoon over left harpoon [(Zr(6)BCl(12))(AlCl(4))(6)](5)(-), E(1/2) = 0.700 V are clearly observed. These data is consistent with less systematic observations of oxidation of these clusters in solution. No unambiguous one-electron electrochemical reduction nor oxidation is observable for the Fe-centered cluster in the ionic liquids. The half-wave potentials of the above reactions of the Be-, B-, C-, and Mn-centered clusters are controlled largely by clusters' charges. This correlation of redox potentials allows a useful direct comparison with data for related hexanuclear niobium clusters in the literature.

Journal Article↗

PubMed1998

New Layered Zirconium Tellurides: Zr(0.30)ZrTe(2), Zr(0.29)Zr(2)Te(2)As, and NaZr(2)Te(2)As.

The synthesis and crystal structure determinations of Zr(0.30)ZrTe(2) and M(x)Zr(2)Te(2)As (M = Zr, Na) compounds are reported. The structure of Zr(0.30)ZrTe(2) was refined in the hexagonal space group P6(3)mc (No. 186, Z = 2) with lattice parameters a = 3.9840(3) Å and c = 13.366(3) Å; Zr(0.29)Zr(2)Te(2)As was refined in the rhombohedral space group R&thremacr;m (No. 166, Z = 3) with lattice parameters a = 3.9329(4) Å and c = 29.564(5) Å. Zr(0.30)ZrTe(2) and Zr(0.29)Zr(2)Te(2)As have close structural similarities to Zr(2)Se(3) and Ta(2)S(2)C, respectively, and are built up by stacking hexagonal layers with [Zr(0.30)-Te-Zr-Te] and [Zr(0.29)-Te-Zr-As-Zr-Te] sequences. Four-probe resistivity measurements (77-300 K) show both Zr(0.30)ZrTe(2) and Zr(0.29)Zr(2)Te(2)As to be metallic (Zr(0.29)Zr(2)Te(2)As: 8.9 x 10(-)(5) Omega cm at 273 K). Both compounds exhibit structures wherein Zr atoms are included between layers (ZrTe(2) and Zr(2)Te(2)As) by partially filling trigonal antiprismatic holes. The replacement of the included Zr ions in Zr(0.29)Zr(2)Te(2)As by Na ions has been demonstrated. Powder diffraction data showed that NaZr(2)Te(2)As is isostructural with Zr(0.29)Zr(2)Te(2)As. By use of Rietveld refinements, sodium ions were found to reside in the trigonal antiprismatic sites between the layers. Extended Hückel band calculations on the [Zr(2)Te(2)As](1.16)(-) layer indicate that it should be a metallic conductor and that the [Zr(2)Te(2)As] layer can bear a greater negative charge than has so far been observed. We suggest that the [Zr(2)Te(2)As] layered compounds may offer new opportunities as electron-donating hosts.

Journal Article↗

PubMed1996

New Zr(6)MTe(2) (M = Mn, Fe, Co, Ni, Ru, Pt), Zr(6)Fe(0.6)Se(2.4), and Zr(6)Fe(0.57)S(2.43) Intermetallics: Structural Links between Binary (Zr,Hf)(3)M Alloys and Porous Metal-Rich Tellurides.

The synthesis of the group IV ternary chalcogenides Zr(6)MTe(2) (M = Mn, Fe, Co, Ni, Ru, Pt) and Zr(6)Fe(1)(-)(x)()Q(2+)(x)() (Q = S, Se) is reported, as are the single-crystal structures of Zr(6)FeTe(2), Zr(6)Fe(0.6)Se(2.4), and Zr(6)Fe(0.57)S(2.43). The structure of Zr(6)FeTe(2) was refined in the hexagonal space group P&sixmacr;2m (No. 189, Z = 1) with lattice parameters a = 7.7515(5) Å and c = 3.6262(6) Å, and the structures of Zr(6)Fe(0.6)Se(2.4) and Zr(6)Fe(0.57)S(2.43) were refined in the orthorhombic space group Pnnm (No. 58, Z = 4) with lattice parameters a = 12.737(2) Å, b = 15.780(2) Å, and c = 3.5809(6) Å and a = 12.519(4) Å, b = 15.436(2) Å, and c = 3.4966(6) Å, respectively. The cell parameters of Mn-, Co-, Ni-, Ru-, and Pt-containing tellurides were also determined. The Zr(6)ZTe(2) compounds are isostructural with Zr(6)CoAl(2), while Zr(6)Fe(1)(-)(x)()Q(2+)(x)() (Q = S, Se) were found to adopt a variant of the Ta(2)P-type structure. Chains of condensed M-centered, tetrakaidecahedra of zirconium constitute the basic structural unit in all these compounds. The modes of cross-linking that give rise to the Zr(6)FeTe(2) and Zr(6)Fe(1)(-)(x)()Q(2+)(x)() structures, differences among the title compounds, and the influence of chalcogen size differences are discussed. The stoichiometric nature of Zr(6)FeTe(2) and its contrast with sulfur and selenium congeners apparently result from a Te-Fe size mismatch. The importance of stabilization of both Zr(6)FeSe(2) and Zr(6)FeTe(2) compounds by polar intermetallic Zr-Fe bonding is underscored by a bonding analysis derived from electronic band structure calculations.

Journal Article↗