Quantum Chemical Modeling of Electrochemical Consecutive Reduction of Fe(III) Aqua- and Aqua-Hydroxocomplexes

Abstract

Quantum chemical modeling of Fe(III), Fe(II), and Fe(I) aqua-, aqua-hydroxo-, and aquadihydroxocomplexes is presented. The mechanism of a consecutive transfer of two electrons is studied as these forms are electrochemically reduced from an aqueous solution. The reorganization energy of the solvent and the inner sphere of studied reagents is calculated, standard redox potentials are estimated. Based on Marcus theory, the activation energy of two steps of Fe(III) reduction is estimated and the second electron transfer is shown to be rate controlling, while the energy barrier is increased due to the products of Fe(III) hydrolysis. The model predictions are in qualitative agreement with previously reported experimental data.