Modulation of the rate of electron transfer in the redox reaction of an octahedral Co(III) complex in reverse micellar milieu and presence of salts in ionic micelles

Abstract

Electron transfer reactions have beneficial implications from biological applications to industrial relevance. Several transition metal complexes have been used as model systems for studying electron transfer reactions. We have picked the octahedral Co(III) complexes from among them due to their inert characteristic making them ideal for theoretical and experimental studies. Kinetics of reduction of Co(III) complexes is negligibly affected by reversible electron transfer, incorporation of water molecules, substitution and isomerisation reactions. Herein, such studies have been performed on the reduction of pentamminechlorocobalt(III) nitrate, [Co(NH3)5Br](NO3)2 by Mohr’s (Fe(II)) salt. Effect of ionic micelles on the redox reaction was studied spectrophotometrically and the influence of various soluble salt concentrations on the reaction rate has been monitored. The outcome of the effect of the water pools of anionic reverse micelles of SDS/1-butanol/n-heptane was also monitored and the results were intriguing. The redox reaction in aqueous solution has been parallelly investigated using a theoretical quantum mechanical approach. The analyses of structures of the reactants, transition state, products and calculation of their energies were done using the density functional theory (DFT). The calculated energy values corroborate with the experimental ones. The activation energies were calculated at three levels of ab initio molecular orbital theory [HF, DFT (B3LYP) and MP2] combined with three basis sets (3-21G*, 6-31G* and 6-31+G**).