Synthesis and characterization of binuclear [ONXO]-type amine-bis(phenolate) copper(II) complexes

Dimeric copper(II) complexes [CuII2L2] of a series of amine-bis(phenolate) ligands (H2L) bearing different non- or weakly coordinating side-arms such as ethyl (H2LEt), n-butyl (H2LBu), thiomethyl (H2LSMe) and hydroxyl (H2LOH) were synthesized. They were characterized by X-ray crystallography, UV–Vis, IR and magnetic susceptibility measurements. X-ray analysis revealed complexes in which Cu(II) centers are surrounded by three phenolate oxygen atoms, an amine nitrogen atom and thiomethyl and hydroxyl coordinating groups in Cu2LSMe2 and Cu2LOH2, respectively. Two phenolate bridges hold both copper atoms together to form binuclear [CuII2L2] complexes. To the best of our knowledge, Cu···Cu distances and Cu–O–Cu bridge angles of these complexes are the smallest values, which have been reported for phenoxo-bridged copper complexes to date. Phenolate moieties of the copper complexes can be electrochemically oxidized to phenoxyl radicals. Magnetic studies show that Cu2LEt2 and Cu2LBu2 are rare examples of phenolato-bridged Cu(II) dimer exhibiting ferromagnetic interaction (J = +26.62 and +38.65 cm−1 respectively). In addition, an antiferromagnetic exchange with J values of −65.88 and −2.77 cm−1 was found for Cu2LSMe2 and Cu2LOH2, respectively.