Mixed-Valent Tetracopper Disulfides Supported by a 1,8-Naphthyridine-Based Ligand: Models for Electronic Communication in Biological Copper Systems

Reaction of a dicopper(I) acetonitrile complex ( 1 ) with elemental sulfur resulted in a formally 2Cu I:2Cu II tetracopper mixed-valent μ-disulfide complex ( 2 ). Stoichiometric reduction (with cobaltocene) or oxidation (with Ag[NTf 2 ], [NTf 2 ] = bis(trifluoromethane)sulfonimide) result in reversible interconversions between complex 2, a formally 3Cu I:Cu II species ( 3 ), and a 4Cu I species ( 4 ). Given the isostructural nature of these complexes, the electronic communication between the metal centers of 2, 3, and 4 were spectroscopically investigated with UV–vis and EPR techniques, revealing the relative delocalization of electron holes on all four copper centers of 2 and 3 . Variable temperature magnetometry of 2, 3, and 4 also reveal antiferromagnetic, ferromagnetic, and temperature-independent paramagnetic behavior, respectively. The formally spin-paired (d 10 ) 4 complex 4 displays unusual magnetic behavior, exhibiting field-induced paramagnetism.