Complex Formation of Poly(4-vinylpyridine) with Copper(II) Ion in Mixed Solvent

Abstract

Complex formation of poly(4-vinylpyridine) with Cu(II) ion in a mixed solvent (water–methanol) was investigated potentiometrically, viscometrically, and spectroscopically. Poly(4-vinylpyridinium chloride) was observed to undergo a pH-induced conformational transition. Adding neutral salt caused a reduction in electrostatic repulsion among charges on the polymer chain. The stability of compact form was low, due to hydrophobic interactions among stacked pyridine rings. The maximum average coordination number was nearly three, in spite of the bulky ligand. The polymer chain was constricted by intramolecular complex formation since no charge exists on the ligands. The polymer–metal complex formation was not a stepwise reaction, but a one-step cooperative reaction resulting from the chelate effect of polymer ligands. Formation of an intramoleculer complex for each Cu(II) ion required nine or ten ligand units on the polymer chain, owing to the rigidity of polymer chain and the steric hindrance of bulky pyridine rings.