Abstract
Three Cu complexes (1, 2, 3) with N, O donor ligands having imidazole–phenol moieties 2-(4,5-diphenyl-1H-imidazol-2-yl)phenol (L1H), 4-bromo 2-(4,5-diphenyl-1H-imidazol-2-yl)phenol (L2H) and 1-(4,5-diphenyl-1H-imidazol-2-yl)naphthalene-2-ol (L3H) have been synthesized and characterized by spectroscopic techniques. Molecular structure of one Cu complex (2) has been determined by X-ray crystallography. 2·DMF crystallises in monoclinic P21/c space group with an exactly intermediate geometry between tetrahedral and square planar (τ4=0.5319). The pKa values of the ligands were determined by UV–Vis spectrophotometric titration. The imidazole–phenol ligand exhibit a high sensitivity towards the pH of the solution. pKa of the imidazolium cation is ∼4.1, whereas pKa for the phenolic deprotonation is in the range 10–10.7. Electronic spectra of the complexes consist of a phenoxide to CuII LMCT in the region (490–500nm) and a d–d transition in the range (620–716nm). All the ligands and the complexes exhibit one ligand based oxidation: phenol/phenoxyl radical or phenolate/phenoxyl radical. pH dependent electrochemical study shows the oxidation process is highly pH sensitive. Potential for this oxidation is close to that observed in Galactose oxidase.
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