A Series of Copper Complexes of a Dinucleating Bis(tetradentate) Nitrogen Ligand: Synthesis, Structural, Spectroscopic, Electrochemical, and Magnetic Characterization

The dinucleating ligand susan (= 4,7-dimethyl-1,1,10,10-tetra(2-pyridylmethyl)-1,4,7,10-tetraazadecane has been used for the synthesis of a series of dinuclear CuII complexes with varying exogenous ligands: [(susan){Cu(ACN)}2](ClO4)4, [(susan){CuCl}2]Cl2, [(susan){CuBr}2]Br2, [(susan){Cu(-OH)Cu}](ClO4)3, and [(susan)¬{Cu(-OH)Cu}](PF6)3. In the solid state, the CuII ions are trigonal-bipyramidally coordinated in [(susan){Cu(-OH)Cu}]3+, while they are in a square-pyramidal environment in the other complexes although mononuclear CuII complexes are trigonal-bipyramidal. In solution, all complexes are trigonal-bipyramidal only [(susan){Cu(ACN)}2]4+ is distorted even in solution. The UV-Vis spectra exhibit unique CT transitions, which makes them easy to identify in solution. [(susan){Cu(ACN)}2]4+ exhibits two reversible reductive processes demonstrating the access of a CuICuI complex, whereas the other complexes exhibit only one reductive process. [(susan){Cu(-OH)Cu}](ClO4)3 and [(susan){Cu(-OH)Cu}](PF6)3 exhibit strong antiferromagnetic interactions with coupling constants of J = -247 and -234 cm-1, respectively. These data are compared to mononuclear analogs and discussed with respect on the sterical flexibility of the ligand backbone and influence of intramolecular interaction on the properties of the dinuclear complexes. [(susan){Cu(-OH)Cu}]3+ catalyzes the aerobic oxidation of 3,5-di-tert-butylcatechol in the presence and absence of a base.