Novel copper(II)-dien-imidazole/imidazolate-bridged copper(II) complexes -: Crystal structure of [Cu(dien)(Him)](ClO4)2 and of [(dien)Cu(μ-im)Cu(dien)](ClO4)3, a homobinuclear model for the copper(II) site of the CuZn-superoxide dismutase

The imidazolate-bridged binuclear copper(II)-copper(II) complex [(dien)Cu( mu-im)Cu(dien)](ClO4)(3) and related mononuclear complexes [Cu(dien)(H2O)](ClO4)(2), [Cu(dien)(Him)](ClO4)(2) were synthesized with diethylenetriamine (dien) as capping ligand. The crystal structure of mononuclear [Cu(dien)(Him)](ClO4)(2) and binuclear complex [(dien)Cu([mu-im)Cu(dien)](ClO4)3 have been determined by single crystal X-ray diffraction methods. The mononuclear complex [Cu(dien)(Him)](ClO4)(2) crystallizes in the orthorhombic, Pca2(1) with a = 9.3420(9) Angstrom, b = 12.3750(9) Angstrom, c = 14.0830(9) Angstrom, beta = 90.000(7)degrees and Z = 4 and binuclear complex [(dien)Cu(mu-im)Cu(dien)](ClO4)(3) crystallizes in the monoclinic space group P2(1)/a, with a = 15.017(7) Angstrom, b = 11.938(6) Angstrom, c = 15.386(6) Angstrom, beta = 110.30(4)degrees and Z = 4. The molecular structures show that copper(II) ions in an asymmetrically elongated octahedral coordination (type 4 + 1 + 1) and in binuclear complex Cu(1) atom has a asymmetrically elongated octahedral coordination (type 4 + I + 1) and Cu(2) atom exhibits a square base pyramidal coordination (type 4 + 1). The bridging ligand (imidazolate ion, im) lies nearly on a straight line between two Cu2+, which are separated by 5.812 Angstrom, slightly shorter than the value in copper-copper superoxide dismutase (Cu-2-Cu2SOD). Magnetic measurements and electron spin resonance (ESR) spectroscopy of the binuclear complex have shown an anti ferro magnetic exchange interaction. From pH-dependent cyclic voltametry (CV) and electronic spectroscopic studies the complex has been found to be stable over a wide pH range (7.75-12.50). (C) 2004 Elsevier B.V. All rights reserved.