(116f) DFT Study On Redox-Active Trinuclear Copper(II) Complex

Efforts in mimicking the efficiency of biological enzymes to oxidize organic substrates and transition metal atoms have sparked interest in understanding the underlying mechanism by which these reactions occur. Multicopper oxidases are a group of enzymes that are able to oxidize a variety of different substrates along with the reducing molecular oxygen to water. In this work, quantum mechanical calculations were performed to study a trinuclear-copper complex, which undergoes a reversible one-electron oxidation to yield a mixed-valency compound. Raptis and co-workers have synthesized a crystalline form of this complex experimentally, but it seems to be unstable and reacts with the solvent, acetonitrile. It has been suggested that acetonitrile couples with the pyrazole groups of the tri-copper complex. Such coupling has been observed in the past with several other metals, Ni²⁺, Ru³⁺, etc. but not with Cu(II). The main goal of this project is to understand, at the molecular level, the interactions of acetonitrile with the tri-copper complex, and to derive the reaction mechanism leading to the decomposition of this complex.  Density functional theory (DFT) calculations have been performed using the unrestricted OPBE exchange/correlation functional along with a mix of 6-311+G and LANL2DZ for the basis set. The latter basis set was used solely on the copper atoms. Geometrical optimizations were carried at different spin states, and frequency calculations were used to verify that structures lie in an energy minimum. It has been shown that a possible route for this reaction is through the acetonitrile-oxygen intermediate complex.