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

摘要

Dimeric copper(II) complexes [Cu~(II)_2L_2] of a series of amine-bis(phenolate) ligands (H_2L) bearing different non- or weakly coordinating side-arms such as ethyl (H_2L~(Et)), n-butyl (H_2L~(Bu)), thiomethyl (H_2L~(SMe)) and hydroxyl (H_2L~(OH)) 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 Cu_2L ~(SMe)_2 and Cu_2L~(OH)_2, respectively. Two phenolate bridges hold both copper atoms together to form binuclear [Cu~(II)_2L_2] 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 Cu_2L~(Et)_2 and Cu _2L~(Bu)_2 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 Cu_2L ~(SMe)_2 and Cu_2L~(OH)_2, respectively.