Three Distinct Oxidation\nStates (II/II, II/III, and\nIII/III) of Diorganocopper Complexes

In this report, we present a structurally and spectroscopically\ncharacterized diorganocopper system in three distinct oxidation states:\n[Cu<sup>II</sup>Cu<sup>II</sup>] (<b>1</b>), [Cu<sup>II</sup>Cu<sup>III</sup>] (<b>2</b>), and [Cu<sup>III</sup>Cu<sup>III</sup>] (<b>3</b>). These states are stabilized by a macrocyclic\nligand scaffold featuring two square-planar coordination {C<sub>2</sub><sup>NHC</sup>N<sub>2</sub><sup>pyrazole</sup>}. We have analyzed\nthe geometric and electronic structures using X-ray diffraction (XRD)\nand multiple spectroscopic methods including nuclear magnetic resonance\n(NMR), UV–vis, and electron paramagnetic resonance (EPR) spectroscopies,\nin combination with density functional theory (DFT) calculations.\nRemarkably, this study provides a structural determination of mixed-valence\ndiorganocopper(II,III) complex <b>2</b>, which is at the borderline\nbetween valence-trapped or charge-localized class I systems and charge\nmoderately delocalized class II systems in Robin and Day classification.\nThese findings enhance our understanding of the systematic structural\nand electronic changes that occur in diorganocopper complexes in response\nto redox transformations.