Monomeric and dimeric mixed-ligand copper(II) complexes of 2,2′-bipyridine/1,10-phenanthroline and 1-methylimidazole with imidazoles as catalysts for superoxide dismutation |
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| Authors: | R. G. Bhirud and T. S. Srivastava |
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| Affiliation: | Department of Chemistry, Indian Institute of Technology, Powai, Bombay, India |
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| Abstract: | Monomeric complexes [Cu(LL)(L′)(NO3)2] (where LL is 2,2′-bipyridine or 1,10-phenanthroline and L′ is 1-methylimidazole) and dimeric complexes [Cu2(LL)2(L″)]NO3 (where L″ is an anion of imidazole or 2-methylimidazole) have been synthesized. These complexes show a d-d transition in the range of 600 to 710 nm. The infrared spectra of monomeric complexes show that the NO3− is coordinated to copper as a monodentate ligand through an oxygen atom. The ESR spectra of monomeric complexes indicate that the ligands are bonded in axial environment around copper (square pyramidal geometry) with three nitrogen donors occupying an equatorial plane. The ESR spectra of dimeric complexes show a broad signal at about G = 2 with an additional weak signal at about G = 4. This suggests that two copper atoms are in close proximity of < 7 Å. The ESR studies reveal that the formation of imidazolate-bridged binuclear copper(II) complexes from [Cu(LL)(L′)(NO3)2] and imidazole is pH dependent with apparent pKa values of 8.25 to 8.30. The superoxide dismutase activity of ICu(phen)(L′)(NO3)2], [Cu(bipy)(L′)(NO3)2], and [Cu2(bipy)2(L′)2(L″)]NO3 has been measured and the latter two complexes show better activity than the former complex. |
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