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(Ln)2 composition. With cupric perchlorate square-pyramidal [CuII(HLn)(NCCH3)(OClO3)]ClO4 complexes (n = 1, 3, 4) were isolated as perchlorate salts, whereas with chloride CuII(HLn)Cl2 (n = 1, 4), or square-planar CuIICl2(HLn) (n = 2, 3, 7) complexes are formed. The X-ray crystal structures of Cu(L3)2, Cu(L5)2, [CuII(HL4)(NCCH3)(OClO3)]ClO4, CuIICl(L2) and CuIICl(L7) 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 [CuII(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.