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.