Highly selective ion sorption and exchange by crystalline zinc complexes of unsymmetrical angular ligand 3-hydroxy-2-quinoxalinecarboxylic acid

With the motivation of searching for highly selective ion sorbents, two new supramolecular complexes, [Zn(qc)2(H2O)2]·H2O·CH3OH (1) and [Zn(qc)2(4,4′-bpy)]n (2) have been synthesized and structurally characterized by assembly of 3-hydroxy-2-quinoxalinecarboxylic acid (Hqc) with Zn(II) at ambient conditions. Complex 1 has a discrete mononuclear moiety, whereas 2 possesses a 1-D polymeric chain structure. Interestingly, complex 1 exhibits highly selective ion sorption and exchange capacity for Cd2+ and Cu2+ over Co2+ and Ni2+ ions in the crystalline solid state when the crystals of 1 is immersed in the aqueous solutions of the perchlorate salts of Cd2+, Cu2+, Co2+ and Ni2+ ions, respectively, which indicates that ion sorption and central Zn(II) ion exchange might be considered as being dominated by the coordination ability of metal ions to free functional groups, ionic radii of adsorbed metal ions, and the solution concentration of adsorbed metal salts. Thermal stabilities and solid state fluorescent properties of the title complexes have been studied.