Heterospin Cobalt, Nickel, and Copper Complexes: 4-TEMPO-oxy-3,6-di-tert-butyl-o-Benzoquinone Derivatives

A series of heterospin bis-o-semiquinone cobalt, nickel, and copper complexes (4-TEMPO-oxy-3,6-di-tert-butyl-o-benzoquinone derivatives) is synthesized: (DMSO)Cu(4-TEMPO-O-3,6-DBSQ)₂ (I), (THF)₂Ni(4-TEMPO-O-3,6-DBSQ)₂ (II), (Py)₂Ni(4-TEMPO-O-3,6-DBSQ)₂ (III), and (Py)₂Ni(4-TEMPO-O-3,6-DBSQ)₂ (IV) (4-TEMPO-O-3,6-DBQ is 4-(3,6-di-tert-butyl-1,2-dioxocyclohexa-3,5-dien-4-yloxy)-2,2,6,6-tetramethylpiperidine-1-oxyl 4-oxy-2,2',6,6'-tetramethylpiperidine-1-oxyl). All complexes are characterized by elemental analysis, IR spectroscopy, magnetochemistry, and EPR. The structure of complex I is determined by X-ray diffraction analysis (CIF file CCDC no. 1882878). The coordination polyhedron of the copper atom in the molecular structure of the Cu(II) bis-o-semiquinone complex with dimethyl sulfoxide (DMSO) is a distorted tetragonal pyramid, whose equatorial plane contains the o-semiquinone ligands, and the DMSO molecule occupies the apical position. The magnetic properties of complexes I–IV are consistent with their compositions and structures. The magnetic behavior of copper complex I and nickel complexes II and III is determined by the balance of two contributions: metal–ligand ferromagnetic exchange interaction and ligand–ligand antiferromagnetic interaction. The temperature dependence of the magnetic moment of cobalt complex IV shows the redox isomeric transformation conjugated with the spin transition, which is characteristic of complexes of this type. No participation of nitroxyl radical centers is observed in intermolecular coordination.