Novel copper(II)-dien-imidazole/imidazolate-bridged copper(II) complexes

The imidazolate-bridged binuclear copper(II)-copper(II) complex [(dien)Cu(μ-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(μ-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, Pca21 with a=9.3420(9) Å, b=12.3750(9) Å, c=14.0830(9) Å, β=90.000(7)° and Z=4 and binuclear complex [(dien)Cu(μ-im)Cu(dien)](ClO4)3 crystallizes in the monoclinic space group P21/a, with a=15.017(7) Å, b=11.938(6) Å, c=15.386(6) Å, β=110.30(4)° 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+1+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 Å, slightly shorter than the value in copper-copper superoxide dismutase (Cu2-Cu2SOD). Magnetic measurements and electron spin resonance (ESR) spectroscopy of the binuclear complex have shown an antiferromagnetic 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).