The reaction of nickel(II) with 2,2?-bipyridyl in methanol- and in dimethyl sulphoxide-water mixtures: Solvent effects on reactivity

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Enthalpies of solution (298 K) are reported for NiCl2 · 6H2O, CoCl2 · 6H2O, and FeCl2 · 4H2O in aqueous methanol (0–40% methanol) and for NiCl2 · 6H2O, 2,2′-bipyridyl, and water in aqueous dimethyl sulphoxide (0–60% DMSO). Solubilities (298 K) of 2,2′-bipyridyl are reported for aqueous dimethyl sulphoxide (0–60% DMSO). From these, from appropriate published thermodynamic data, and from published rate constants and activation enthalpies, we have analysed solvent effects on reactivities (μ and H) into initial state and transition state contributions (the latter are in fact composite ion-association and interchange quantities). In all systems examined the observed kinetic trends represent small differences between large and almost identical solvent effects on the respective initial and transition states.