Tetra-, penta- and hexacoordinate copper(II) complexes with N3 donor isoindoline-based ligands: Characterization and SOD-like activity

Reaction of 1,3-bis(2'-Ar-imino)isoindolines (HLn, n = 1-7, Ar = benzimidazolyl, N-methylbenzimidazolyl, thiazolyl, pyridyl, 3-methylpyridyl, 4-methylpyridyl, and benzthiazolyl, respectively) with Cu(OCH3)(2) yields mononuclear hexacoordinate complexes with Cu(L-n)(2) composition. With cupric perchlorate square-pyramidal [Cu-II(HLn)(NCCH3)(OClO3)]ClO4 complexes (n = 1, 3, 4) were isolated as perchlorate salts, whereas with chloride Cu-II(HLn)Cl-2 (n = 1, 4), or square-planar (CuCl2)-Cl-II(HLn) (n = 2, 3, 7) complexes are formed. The X-ray crystal structures of Cu(L-3)(2), Cu(L-5)(2), [Cu-II(HL4)(NCCH3)(OClO3)]ClO4, (CuCl)-Cl-II(L-2) and (CuCl)-Cl-II(L-7) are presented along with electrochemical and spectral (UV-Vis, FT-IR and X-band EPR) characterization for each compound. When combined with base, the isoindoline ligands in the [Cu-II(HLn)(NCCH3)(OClO3)]ClO4 complexes undergo deprotonation in solution that is reversible and induces UV-Vis spectral changes. Equilibrium constants for the dissociation are calculated. X-band EPR measurements in frozen solution show that the geometry of the complexes is similar to the corresponding X-ray crystallographic structures. The superoxide scavenging activity of the compounds determined from the McCord-Fridovich experiment show dependence on structural features and reduction potentials. (C) 2011 Elsevier B.V. All rights reserved.