Syntheses, crystal structures, adsorption properties and visible photocatalytic activities of highly stable Pb-based coordination polymers constructed by 2-(2-carboxyphenyl)imidazo (4,5-f)-(1,10) phenanthroline and bridging linkers

Five highly stable coordination polymers assembled by 2-(2-carboxyphenyl) imidazo(4,5-f)-(1,10) phenanthroline (2-HNCP) and different aromatic carboxylic acid ligands, namely, [Pb(2-NCP)(L-1)](n) (1), [Pb-2(2-NCP)(2)(L-2)](n)center dot 2nH(2)O (2), [Pb-2(2-NCP)(2)(L-2)](n) (3), [Pb(2-NCP)(L-3)(0.5)](n) (4) and [Pb-2(2-NCP)(2)(L-4)](n) (5), where HL1 = pyridine-4-carboxylic acid, H2L2 = 2-amino-1,4-benzenedicarboxylic acid, H2L3 = 1,4-benzenedicarboxylic acid and H2L4 = 2-hydroxy-1,4-benzenedicarboxylic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses and infrared spectroscopy. In 1, adjacent ladder-like chains are extended into a three-dimensional (3D) supramolecular architecture by pi-pi interactions. In 2, the neighboring layers are interconnected by pi-pi interactions to afford a 3D supramolecular architecture. 3-5 exhibit similar 3D frameworks with a Schlafli symbol of 4(12).6(3) topologies. The different auxiliary ligands and the pH value of the reaction system were discussed in regard to the formation of different structures. In addition, these five complexes present high thermal stabilities, the preferential adsorption of CO2 over N-2 and excellent photocatalytic activities for dye degradation under visible light irradiation.