Electrochemical Mechanisms of Copper Bipyridine Complexes in Dichloromethane and Water

Abstract

Voltammetric mechanisms for copper bipyridine complexes are evaluated for Cu(bpy)3(PF6)2 in dichloromethane (DCM), Cu(bpy)3(ClO4)2 in water, and copper bipyridine complexes formed in situ from a stoichiometric 1:3 mix of Cu(II) and bpy in water. The mechanism for Cu(bpy)3(PF6)2 in aprotic DCM is a simple irreversible (slow) heterogeneous electron transfer, Eirrev , with a standard heterogeneous electron transfer rate of 6 × 10−4 cm s−1. For Cu(bpy)3(ClO4)2 in water near pH 6, the mechanism is a six species square scheme, with multiple chemical and electrochemical steps. Voltammetric morphologies for Cu(bpy)3(PF6)2 in DCM and Cu(bpy)3(ClO4)2 in water were evaluated by established diagnostics and modeled with digital simulations. Established diagnostics underrepresent the complexity of copper bipyridines in water. For the complexes formed in situ, the stoichiometric ratio is insufficient to form only Cu(bpy)3 2+, so an equilibrium model that characterizes speciation at given pH and electrode potentials is used. Solvent, pH, and speciation impact the observed voltammetry of copper bipyridine complexes.