Coordination polymers of sodium 2-(quinolin-8-yloxy)propionate: A receptor for selective metal ions

Abstract

Unusual bifurcated and trifurcated carboxylate binding to sodium ions in a one dimensional coordination polymer, [{Na2L(H2O)3}Br·H2O]n (1) (where L=2-(quinolin-8-yloxy)propionate), was observed. The ionic coordination polymer 1, possessing bromide anions, has sodium ions in two independent coordination environments. Reaction of 1 with perchloric acid led to anion exchange to form the dinuclear complex [Na2(HL)2(ClO4)2(μ-H2O)] (2). A cadmium coordination polymer [Cd(L)Br]n (3) was prepared by reacting 1 with cadmium(II) acetate. This one dimensional cadmium coordination polymer 3 has cadmium ions in a distorted square pyramidal geometry. The uniqueness of the cadmium polymer is that the bromide ions are inside the coordination sphere and it forms parallel sheet-like structures of polymeric chains through bromide–bromide interactions. The coordination polymer 1 and the dinuclear complex 2 are weakly fluorescent, whereas complex 3 is highly fluorescent. The coordination polymers 1 and 2 are fluorescence receptors for Mg, Ca, Ba, Zn, Cd and Hg in the (+2) oxidation state.