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

Abstract

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.