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

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, Cu2L2, Cu2LH-1) are formed in the Cu(II)-biib system. Since the biib offers extremely stable tri- and tetradentate coordination to copper(II) tin CuLH and Cu2L2, 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. (C) 1998 Elsevier Science Inc. All rights reserved.