Fine-Tuning the Electronic Properties of Highly Stable Organometallic CuIII Complexes Containing Monoanionic Macrocyclic Ligands

A family of highly stable organometallic Cu^III complexes with monoanionic triazamacrocyclic ligands (Li) with general formula [CuLi]⁺ have been prepared and isolated, and their structural, spectroscopic, and redox properties thoroughly investigated. The HLi ligands have been designed in order to understand and quantify the electronic effects exerted by electron donor and electron-withdrawing groups on either the aromatic ring or the central secondary amine or on both. In the solid state the CuIII complexes were mainly characterized by single-crystal X-ray diffraction analysis, whereas in solution their structural characterization was mainly based on ¹H NMR spectroscopy given the diamagnetic nature of the d⁸ square-planar Cu^III complexes. Cyclic voltammetry together with ¹H NMR and UV/Vis spectroscopy have allowed us to quantify the electronic effects exerted by the ligands on the Cu^III metal center. A theoretical analysis of this family of Cu^III complexes has also been undertaken by DFT calculations to gain a deeper insight into the electronic structure of these complexes, which has in turn allowed a greater understanding of the nature of the UV/Vis transitions as well as the molecular orbitals involved.