Three novel topologically different metal-organic frameworks built from 3-nitro-4-(pyridin-4-yl)benzoic acid

The design and synthesis of metal-organic frameworks (MOFs) have attracted much interest due to the intriguing diversity of their architectures and topologies. However, building MOFs with different topological structures from the same ligand is still a challenge. Using 3-nitro-4-(pyridin-4-yl)benzoic acid (HL) as a new ligand, three novel MOFs, namely poly[[(N,N-dimethylformamide-κO)bis[μ₂-3-nitro-4-(pyridin-4-yl)benzoato-κ³O,O':N]cadmium(II)] N,N-dimethylformamide monosolvate methanol monosolvate], {[Cd(C₁₂H₇N₂O₄)₂(C₃H₇NO)]·C₃H₇NO·CH₃OH}_n, (1), poly[[(μ₂-acetato-κ²O:O')[μ₃-3-nitro-4-(pyridin-4-yl)benzoato-κ³O:O':N]bis[μ₃-3-nitro-4-(pyridin-4-yl)benzoato-κ⁴O,O':O':N]dicadmium(II)] N,N-dimethylacetamide disolvate monohydrate], {[Cd₂(C₁₂H₇N₂O₄)₃(CH₃CO₂)]·2C₄H₉NO·H₂O}_n, (2), and catena-poly[[[diaquanickel(II)]-bis[μ₂-3-nitro-4-(pyridin-4-yl)benzoato-κ²O:N]] N,N-dimethylacetamide disolvate], {[Ni(C₁₂H₇N₂O₄)₂(H₂O)₂]·2C₄H₉NO}_n, (3), have been prepared. Single-crystal structure analysis shows that the Cd^II atom in MOF (1) has a distorted pentagonal bipyramidal [CdN₂O₅] coordination geometry. The [CdN₂O₅] units as 4-connected nodes are interconnected by L^- ligands to form a fourfold interpenetrating three-dimensional (3D) framework with a dia topology. In MOF (2), there are two crystallographically different Cd^II ions showing a distorted pentagonal bipyramidal [CdNO₆] and a distorted octahedral [CdN₂O₄] coordination geometry, respectively. Two Cd^II ions are connected by three carboxylate groups to form a binuclear [Cd₂(COO)₃] cluster. Each binuclear cluster as a 6-connected node is further linked by acetate groups and L^- ligands to produce a non-interpenetrating 3D framework with a pcu topology. MOF (3) contains two crystallographically distinct Ni^II ions on special positions. Each Ni^II ion adopts an elongated octahedral [NiN₂O₄] geometry. Each Ni^II ion as a 4-connected node is linked by L^- ligands to generate a two-dimensional network with an sql topology, which is further stabilized by two types of intermolecular OW-HW...O hydrogen bonds to form a 3D supramolecular framework. MOFs (1)-(3) were also characterized by powder X-ray diffraction, IR spectroscopy and thermogravimetic analysis. Furthermore, the solid-state photoluminescence of HL and MOFs (1) and (2) have been investigated. The photoluminescence of MOFs (1) and (2) are enhanced and red-shifted with respect to free HL. The gas adsorption investigation of MOF (2) indicates a good separation selectivity (71) of CO₂/N₂ at 273 K (i.e. the amount of CO₂ adsorption is 71 times higher than N₂ at the same pressure).