Copper Complexes of New Redox-Active 4,5-Bisguanidino-Substituted Benzodioxole Ligands: Control of the Electronic Structure by Counter-Ligands, Solvent, and Temperature

Herein, we analyze the possibility of controlling the electronic structure of mononuclear copper complexes featuring new redox-active 4,5-bisguanidino-substituted benzodioxole ligands. The nature of the guanidino groups, the anionic counter-ligands, the applied solvent (polarity), and the temperature are the parameters that decide if a Cu-II complex with neutral ligand unit or a Cu-I complex with radical monocationic ligand unit is the adequate description. Under special conditions, a temperature-dependent equilibrium of the two valence tautomeric forms (Cu-II/neutral ligand and Cu-I/radical monocationic ligand) is achieved. Removal of a ligand-centered electron from a paramagnetic Cu-II complex with a neutral ligand unit leads to a diamagnetic Cu-I complex with a dicationic ligand unit through a redoxinduced electron-transfer (RIET) process.