On the complexation of Ag(I) and Cu(II) ions with poly(N-vinylimidazole)

Complexation equilibria of Ag(I) and Cu(II) ions with poly(N-vinylimidazole) have been investigated potentiometrically by measuring concurrently the pH and pM (M = Ag(I), Cu(II)) of the equilibrium mixture solutions of the linear polymer and metal ions in the presence of sodium nitrate at 25 degrees C. The equilibria were highly sensitive to the degree of dissociation of the conjugate acid of the polymer as well as the sodium nitrate concentration level, mainly due to the polyelectrolytic nature of the polymer, however, by correcting for this electrostatic effect based on a 'Donnan-based concept', insights into the intrinsic complexation equilibria have been gained, i.e, the electrostatic non-ideality term has properly been estimated by the use of the acid-dissociation property of the conjugate acid polymer asa probe. Multidentate complex formation with neighboring imidazole groups on the polymer molecules has been revealed for both complexation systems at fully dissociated states, i.e. two imidazole groups are involved in Ag+ ion complexation and four groups in Cu2+ ion complexation, respectively. The intrinsic formation constants of the polymer complexes thus evaluated were compared with the reported formation constants for respective multidentate complexes with imidazole ligand, a monomer analog of the polymer molecule. The coordination number decreased stepwisely with a decrease in the degree of dissociation of the conjugate acid for both metal complexation systems. (C) 1998 Elsevier Science B.V. All rights reserved.