Iron(II) coordination to bipyridyl-based hydrogel polymers

Hydrophilic membranes composed of copolymers of 0.3% by weight 4-methyl-4'-vinyl-2, 2'-bipyridyl with 2-hydroxyethyl methacrylate were prepared, and the coordination of iron(II) from aqueous solutions of the sulfate, perchlorate and chloride salts to form the tris(2,2'-bipyridyl)iron(II) species was studied at a range of temperatures in order to extend earlier findings. In the case of the chloride the rate equation was found to differ from that previously reported. Values for the enthalpy and entropy changes for an equilibrium involving the obstruction of potential ligand sites by existing coordination centres, and the activation enthalpies and entropies for the slow steps during complex formation, are determined. They are interpreted as showing that the slow steps in all cases involve segmental rotation within the copolymer chains to permit further coordination to occur. Copyright (C) 1996 Elsevier Science Ltd.