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, [M-2(L1)(L2)(2)] (M = Co for 1, Mn for 2, Zn for 3, and Cd for 4), where H(4)L1 = 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 pi-pi interactions between pyridyl groups of L2 ligands. If the pi-pi 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.