Novel Pb(II), Zn(II), and Cd(II) Coordination Polymers Constructed from Ferrocenyl-Substituted Carboxylate and Bipyridine-Based Ligands

Treatment of two kinds of ferrocenyl-substituted carboxylate ligands (3-ferrocenyl-2-crotonic acid, HOOC-CH=(CH3)CFc (Fc=((eta)^5C5H5)Fe(5-C5H4)) or O-ferrocecarbonyl benzoic acid, o-HOOCC6H4COFc with Pb(OAc)2·3H2O, Zn(OAc)2·2H2O, or Cd(OAc)2·2H2O) resulted in four novel ferrocene-containing coordination polymers {[Pb((mu)2(eta)^2-OOCCH=(CH3)CFc)2]·MeOH}n (1), {[Zn(oOOCC6H4COFc)2(4,4ʹ-bipy)(H2O)2]·2MeOH·2H2O}n (4,4ʹ-bipy = 4,4ʹ-bipyridine) (2), {[Cd(o-OOCC6H4COFc)2(bpe)(MeOH)2]·2H2O}n (bpe=1,2-bis(4-pyridyl)ethene) (3), and [Pb(o-OOCC6H4COFc)(2-o-OOCC6H4COFc)(bpe)]n (4). Their crystal structures have been characterized by single X-ray determinations. In polymer 1, Pb(II) ions are bridged by tridentate FcC(CH3)=CHCOO^- anions, forming an infinite chain [Pb((mu)2-(eta)^2-OOC=CH(CH3)CFc)2]n. In polymers 2-4, there are three kinds of components, metal ions, oFcCOC6H4COO^- units, and organic bridging ligands. The bipyridine-based ligands connect metal ions leading to a one-dimensional chain with o-FcCOC6H4COO^- units acting as monodentate or chelate ligands in the side chain. Such coordination polymers containing ferrocenyl-substituted carboxylate and bipyridine-based ligands are very rare. The solution-state differential pulse voltammetries of polymers 1-4 were determined. The results indicate that the half-wave potential of the ferrocenyl moieties is influenced by the Pb(II) ions in polymer 1 and strongly influenced by Zn(II), Cd(II), or Pb(II) ions in polymers 2-4. The thermal properties of the four polymers were also investigated.