Redox behaviour of bis(β-diketonato)copper(II) complexes

Abstract

In this study for the first time, a comprehensive report was compiled on the electrochemical behavior of a series of eight square planar bis(β-diketonato)copper(II) complexes, with a variety of substituents R1 and R2 on the β-diketonato ligand (R1COCHCOR2)−. The character of the observed redox features was determined by computational chemistry calculations of the frontier molecular orbitals involved. The experimentally obtained electrochemically irreversible CuII/CuI reduction potentials, Epc(CuII/CuI), were related to various electronic descriptors (such as electronegativities, Hammett constants and Lever electronic parameters), which describe the electron withdrawing power of the β-diketonato ligands attached to the copper metal. Linear relationships have also been obtained between Epc(CuII/CuI) and computational chemistry calculated energies of the eight bis(β-diketonato)copper(II) complexes. These linear relationships confirmed good communication between the copper metal and the eight different β-diketonato ligands attached to it. Furthermore, the experimentally observed electrochemically irreversible CuII/CuI reduction potentials of those [CuII(β-diketonato)2] complexes which are metal based, were also linearly related to the reduction potentials of the uncoordinated free β-diketones which are ligand based. Furthermore, the DFT calculated LUMO energies reproduce the experimental absolute reduction potential.