Three Distinct Oxidation States (II/II, II/III, and III/III) of Diorganocopper Complexes

Abstract

In this report, we present a structurally and spectroscopically characterized diorganocopper system in three distinct oxidation states: [Cu^IICu^II] (1), [Cu^IICu^III] (2), and [Cu^IIICu^III] (3). These states are stabilized by a macrocyclic ligand scaffold featuring two square-planar coordination {C₂^NHCN₂^pyrazole}. We have analyzed the geometric and electronic structures using X-ray diffraction (XRD) and multiple spectroscopic methods including nuclear magnetic resonance (NMR), UV–vis, and electron paramagnetic resonance (EPR) spectroscopies, in combination with density functional theory (DFT) calculations. Remarkably, this study provides a structural determination of mixed-valence diorganocopper(II,III) complex 2, which is at the borderline between valence-trapped or charge-localized class I systems and charge moderately delocalized class II systems in Robin and Day classification. These findings enhance our understanding of the systematic structural and electronic changes that occur in diorganocopper complexes in response to redox transformations.