Browsing by Author "Irangu, Japhet"

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    Copper-63 NMR line width study of the copper(I)-acetonitrile system
    (2003) Irangu, Japhet
    The principal focus of this study is the 63Cu NMR line widths in Cu(I)−acetonitrile (AN) solutions. The variations with the concentrations of Cu(I) salts (trifluoromethanesulfonate and perchlorate), added salts, water, chloride ion, and temperature have been studied. A quantitative analysis shows that the anomalous temperature dependence of the line widths is not due to ion pairing or anion complexation but results primarily from formation of a species with a different coordination number or less symmetrical arrangement of AN ligands than in the normal tetrahedral Cu(AN)4+ ion. Solvent viscosity and ion pairing (with triflate) also are identified as factors having the expected effects on the line widths. The results of earlier studies also are discussed and analyzed by the current model where possible.
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    Reaction of copper(II) with ferrocene and 1,1 '-dimethylferrocene in aqueous acetonitrile: the copper(II/I) self-exchange rate
    (2005) Irangu, Japhet; Ferguson, Michael J.; Jordan, Robert B.
    The kinetics of the reactions of copper(II) with ferrocene (Fc) and 1,1‘-dimethylferrocene (Dmfc) have been studied at 25 °C in aqueous acetonitrile (AN) containing 50−97.5 vol % AN. With increasing % AN, the rate constant increases along with the driving-force for the reaction. The results are analyzed in terms of Marcus theory to estimate the Cu(II/I) electron self-exchange rate constant (k11) for the system. Over the solvent range studied, the calculated k11 changes from 1.1 × 10-9 to 17 × 10-9 M-1 s-1, with an average value of 5 × 10-9. In addition, the structures of the trifluoromethanesulfonate salts of [Cu(AN)4]+, [Cu(OH2)2(AN)2]2+, and [Cu(AN)4]2+ are reported. It is found that the Cu−NCCH3 bond-length difference between the Cu(I) and Cu(II) oxidation states is only ∼0.02 Å.