Electron Transfer Reaction of Tris(1,10-phenanthroline)cobalt(III) Complex and Iodide Ion in An Aqueous Acidic Medium

Abstract

The kinetics and mechanistic study of the electron transfer of tris(1,10-phenanthroline)cobalt(III) complex and iodide ion has been carried out in an aqueous acidic medium at ionic strength(I) = 0.20 mol dm−3 (NaCl), [H+] = 0.02 mol dm−3, T = 28 ± 1.0 °C and λmax of 495 nm. The rate of reaction was found to be third order overall: first order in the oxidant and second order in the reductant, and acid independent. The empirical rate law conforms to the equation: $$- = {\text{ k}}[({\text{Co}}\left( {{\text{phen}}} \right)_{{3}} )^{{{3} + }} ]\left[ {{\text{I}}^{ - } } \right]^{{2}}$$ The reaction rate was unaffected by change in ionic strength and dielectric constant of the reaction medium. Added cations and anions catalysed and inhibited the reaction rate respectively. Based on spectroscopic investigation and kinetic pieces of evidence from the Michaelis–Menten plot and effect of added ions, an outer sphere mechanism has been rationalised for the reaction.