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

Abstract

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(MeCN)}2](ClO4)4, [(susan){CuCl}2]Cl2, [(susan){CuBr}2]Br2, [(susan){Cu(µ‐OH)Cu}](ClO4)3, and [(susan){Cu(µ‐OH)Cu}](PF6)3. In the solid state, the CuII ions are trigonal‐bipyramidally coordinated in [(susan){Cu(µ‐OH)Cu}]3+, whereas 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(MeCN)}2]4+ is distorted even in solution. The UV/Vis spectra exhibit unique charge‐transfer (CT) transitions, which make them easy to identify in solution. Complex [(susan){Cu(MeCN)}2]4+ exhibits two reversible reductive processes, demonstrating access to a CuICuI complex, whereas the other complexes exhibit only one reductive process. Complexes [(susan){Cu(µ‐OH)Cu}](ClO4)3 and [(susan){Cu(µ‐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 to the steric flexibility of the ligand backbone and influence of intramolecular interactions on the properties of the dinuclear complexes. Complex [(susan){Cu(µ‐OH)Cu}]3+ catalyzes the aerobic oxidation of 3,5‐di‐tert‐butylcatechol in the presence and absence of a base.