Synthesis and electron transfer kinetics of a surfactant–cobalt(III) complex: effects of micelles, β-cyclodextrin, and ionic liquids

Abstract

A surfactant–cobalt(III) complex, cis-[Co(en)2(4AMP)(DA)](ClO4)3, (en = ethylenediamine, 4AMP = 4-aminopyridine, DA = dodecylamine), was synthesized and characterized by physicochemical and spectroscopic methods. The critical micelle concentration (CMC) value of this surfactant–cobalt(III) complex in aqueous solution was obtained from conductance measurements. Conductivity data were used for evaluation of the temperature-dependent CMC and the thermodynamics of micellization (\( \Updelta {\text{G}}_{\text{m}}^{ 0} \), \( \Updelta {\text{H}}_{\text{m}}^{0} \), and \( \Updelta {\text{S}}_{\text{m}}^{0} \)). The kinetics of reduction of this surfactant–cobalt(III) complex by ion(II) in micelles, β-cyclodextrin (β-CD), and ionic liquid (IL) were studied. The reaction was found to be second order, and the electron transfer is postulated as outer sphere. The second-order rate constant for the electron transfer reaction was found to increase with increasing concentration of IL, but inclusion of the long aliphatic chain of the surfactant complex into β-CD decreases the rate of the reaction. The results have been interpreted in terms of the amphiphilicity of the surfactant complex.