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)(L1)]n (1), [Pb2(2-NCP)2(L2)]n·2nH2O (2), [Pb2(2-NCP)2(L2)]n (3), [Pb(2-NCP)(L3)0.5]n (4) and [Pb2(2-NCP)2(L4)]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 π-π interactions. In 2, the neighboring layers are interconnected by π-π interactions to afford a 3D supramolecular architecture. 3-5 exhibit similar 3D frameworks with a Schläfli symbol of 412·63 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 N2 and excellent photocatalytic activities for dye degradation under visible light irradiation.