Nickel(II)-, copper(II)- and zinc(II)-complexes of some substituted imidazole ligands

Abstract Nickel(II)-, copper(II)- and zinc(II)-complexes of four imidazole derivatives (4(5)-aminoimidazole-5(4)-carboxamide (aic), 2,2′-biimidazole (biim), bis(1,1′-imidazol-2-yl)(4-imidazol-4(5)-yl)-2-aza-butane (biib) and imidazole-4-acetic acid (iaa)), having different coordination environments around the imidazole ring(s), have been studied by potentiometric, UV–VIS and EPR spectroscopic methods. The data revealed very strong bidentate coordination of biim, in spite of the low basicity of the donor sites. Three dominant species (CuLH, Cu 2 L 2 , Cu 2 LH −1 ) are formed in the Cu(II)-biib system. Since the biib offers extremely stable tri- and tetradentate coordination to copper(II) (in CuLH and Cu 2 L 2 , respectively), the bis-imidazolyl like coordination, which is predominant in metal complexes of any other bis-imidazolyl like ligand, does not appear in its original form in the copper(II)-biib system. The EPR spectra of above dimer species show coupling between the copper(II) centers. In the M(II)-iaa systems only parent complexes are formed up to pH 9, while at higher pH further deprotonations were observed, which resulted in a formation of dimer complexes in case of copper(II), having antiferromagnetically coupled metal centers.