Octahedral cobalt(III) complexes of the chloropentammine type. Part XIV. Base hydrolysis of some halogenopentamminecobalt(III) and halogenopentamminechromium(III) cations in aqueous alcohols

Abstract

The second-order rate constants for the base hydrolysis of chloro- and fluoro-pentamminecobalt(III) and the corresponding chromium(III) cations in mixed solvents have been determined over a range of temperatures and the Arrhenius parameters have been calculated. The reaction media used were mixtures of methanol (or ethanol) with water in the mole ratio 1 : 4·5. The higher rates in these solvents compared with those in water are apparently compatible with both the conjugate-base and the ion-pair mechanisms of octahedral base hydrolysis. Since, for the corresponding hexammine type of cations in alkaline solutions, spectroscopic evidence points to the presence of the ion-pair, and not the conjugate-base, the kinetic results are discussed in terms of the ion-pair mechanism.