Kinetics and Thermodynamics of Formation and Electron‐Transfer Reactions of Surfactant Cobalt(III) Complexes Containing Polypyridyl Ligands with Fe(CN)₆⁴⁻in Microheterogeneous Environment

Abstract

The electron‐transfer reaction of some surfactant cobalt(III) complexes, cis‐[Co(ip)2(C12H25NH2)2]3+ 1, cis‐[Co(dpq)2(C12H25NH2)2]3+ 2, and cis‐[Co(dpqc)2(C12H25NH2)2]3+ 3 (ip = imidazo[4,5‐f][1,10]phenanthroline, dpq = dipyrido[3,2‐d:2′‐3′‐f]quinoxaline, dpqc = dipyrido[3,2‐a:2′,4′‐c](6,7,8,9‐tetrahydro)phenazine, C12H25NH2 = dodecylamine) with the Fe(CN)64− ion has been investigated in microheterogeneous media (micelles, β‐cyclodextrin) at different temperatures by the spectrophotometric method under pseudo‐first‐order conditions using an excess of the reductant. Experimentally, the reaction was found to be second order and the electron transfer postulated as an outer sphere. The rate constant for the electron‐transfer reaction in micelles was found to increase with an increase in the initial concentration of the surfactant–cobalt(III) complex. This peculiar behavior of dependence of the second‐order rate constant on the initial concentration of one of the reactants has been attributed to the presence of various concentrations of micelles under different initial concentrations of the surfactant–cobalt(III) complex in the reaction medium. Inclusion of the long aliphatic chain of the surfactant complex ion into β‐cyclodextrin leads to decrease in the rate constant. Kinetic data and activation parameters are interpreted in terms of an outer‐sphere electron‐transfer mechanism. All these results have been interpreted in terms of the hydrophobic effect and the reactants with the opposite charge.