Molecular Tectonics of Mixed-Ligand Metal−Organic Frameworks: Positional Isomeric Effect, Metal-Directed Assembly, and Structural Diversification

A series of nine mixed-ligand metal−organic frameworks (MOFs) have been prepared by the combination of a bent
dipyridyl linker 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole (bpt) and three benzenedicarboxylate isomers (pa = phthalate,
ip = isophthalate, and tp = terephthalate), respectively, with different metal ions such as CoII, NiII, CuII, ZnII, and
CdII. The framework structures of these neutral polymeric complexes have been determined by the X-ray single-crystal diffraction technique. Structural analysis reveals that the benzenedicarboxylate isomers display versatile
coordination modes to manage the metal ions to form 1-D chain or ribbon arrays, which are further extended via
the exo-bidentate bpt connectors to give rise to a variety of coordination networks, such as a simple (4,4) layer,
2-D double layer with decorated (4,4) topology, 2-D layer with decorated (3,6) topology, 2-D bilayer with 82.10
topology (2-fold interpenetration), 3-D polythreaded architecture (1-D + 2-D), and 2-fold interpenetrating porous
lattice of (4,4) layers. The accessorial secondary interactions such as hydrogen bonding and/or aromatic stacking
are also helpful for the extension and stabilization of the final supramolecular aggregates. This work evidently
indicates that the isomeric effect of the anionic benzenedicarboxylate is significant in the construction of these
network structures, which are also well regulated by the metal centers. The ZnII and CdII MOFs exhibit strong
solid-state luminescence emissions at room temperature, which originate differently from intraligand transition or
ligand-to-metal charge transfer. Thermal stability of these crystalline materials has been explored by thermogravimetric
analysis of mass loss. The 3-D host frameworks of MOFs 8 and 9 show similar porous cavities, and their desorption/adsorption behaviors of guest solvents have also been investigated.