Copper(II) and Copper(I) Complexes with an Open-Chain N4 Schiff Base Ligand Modeling CuZn Superoxide Dismutase: Structural and Spectroscopic Characterization and Kinetics of Electron Transfer

The structure of the complex [CuII(PuPy)](ClO4)2 (PuPy = L = 1,8-bis(2-pyridyl)-2,7-diazaoctadiene-1,7) and the structure of the corresponding copper(I) complex were determined. In CuIIL(ClO4)2, a model compound with CuZnSOD activity, the unit CuIIL2+ has a tetrahedrally distorted square-planar N4 coordination geometry. The copper(I) complex with L was found to be dimeric, (CuIL)2(ClO4)2·DMF (DMF = N,N-dimethylformamide). The binuclear unit (CuIL)22+ has a helical structure with two ligands L bridging the two copper atoms to provide tetrahedral N4 coordination of each copper(I). In solutions of (CuIL)2(ClO4)2·DMF, solvent-dependent dissociation occurs according to D ⇌ 2M (D = (CuIL)22+; M = CuILSx+; S = solvent). Stopped-flow spectrophotometry was used to determine the rate constants for the dissociation of the dimer D (kM) and dimerization of the monomer M (kD) for S = acetonitrile and DMF. Equilibrium constants Kdim = kM/kD were determined spectrophotometrically. In aqueous solution, the oxidation of th...