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Unusual 2D → 3D Polycatenane Frameworks Based on 1D → 2D Interdigitated Layers: From Single Crystals to Submicrometer Fibers with Enhanced UV Photocatalytic Degradation Performances
Four unusual isomorphous metal–organic frameworks, [M2(L1)(L2)2] (M = Co for 1, Mn for 2, Zn for 3, and Cd for 4), where H4L1 = tetrakis[4-(carboxyphenyl)-oxamethyl]methane acid and L2 = 4-tolyl-2,2′:6′,2″-terpyridine, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by infrared spectra, elemental analyses, powder X-ray diffraction, UV–vis absorption spectra, and optical energy gaps. In compounds 1–4, the metal atoms are linked by the L1 anions to yield a chain with a loop. Every loop of each chain is penetrated by two L2 ligand rods belonging to the two nearest chains, resulting in an unusual 1D → 2D interdigitated network. In the 2D interdigitated network, there exist weak π–π interactions between pyridyl groups of L2 ligands. If the π–π interactions are regarded as linkers, the 2D interdigitated network belongs to an uneven (3,4)-connected layer. Furthermore, each individual (3,4)-connected layer is polycatenated with an infinite number of other perpendicular layers, yielding an unusual 2D → 3D polycatenane framework. The luminescent properties of compounds 3 and 4 have been studied. In addition, compounds 1–4 exhibit photocatalytic activities for MB degradation under UV irradiation. Submicrometer fiber 1′ shows high photocatalytic efficiency for MB degradation with respect to its corresponding macroscaled crystalline 1.