The complexation of copper (Cu2+), cobalt (Co2+), and cadmium (Cd2+) ions with poly(N-vinylimidazole) (PVIm) and its protonated form in aqueous solution was studied conductometrically and viscometrically. From the conductometric and viscometric curves, it was found that four imidazole units were coordinated with one metal ion in the complex systems. Both studies showed that the complex formation tendency decreased in the following order: Cu2+ > Co2+ > Cd2+. Complex properties of metal ions with imidazole group were explained by referring to Pearson's treatment, as hard and soft acids and bases. (C) 2002 Wiley Periodicals, Inc.