Construction of Metal-Organic Frameworks with 1D Chain, 2D Grid, and 3D Porous Framework Based on a Flexible Imidazole Ligand and Rigid Benzenedicarboxylates

Using ligands BITMB and IPA or TMIPA (BITMB = 1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene, IPA = isophthalic acid, TMIPA = 2,4,6-trimethylisophthalic acid), in which the BITMB can adopts syn or anti conformations, three metal-organic frameworks (MOFs) have been synthesized. These MOFs contain a variety of structures: a one-dimensional (1D) chain (1), two-dimensional (2D) interpenetrating layer (2), and three-dimensional (3D) porous framework (3). In MOFs 1 and 2, the BITMB ligand adopts a syn conformation, connecting metal ions to form a macrometallocycle or chain as the subunit, which are further connected by the rigid carboxylate ligands to generate the final ID chain or 2D interpenetrating layer. The BITMB ligand in 3 adopts an anti conformation, which connects metal ions to form a 1D zigzag chain as the subunit. The 1D chain subunits are further connected by the carboxylate ligand to form the 3D porous framework. The conformation of the BITMB and thus the dimensionality of the MOF can be controlled by the presence or lack of water solvent in the reaction system. Photoluminescence measurements of 2 and 3 in the solid state at room temperature show that both coordination networks exhibit similar, strong luminescence, which can be assigned to an intraligand pi ->pi* transition.