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[μ ₂ -3-nitro-4-(pyridin-4-yl)benzoato-κ ³ O,O′:N]cadmium(II)] N,N-dimethylformamide monosolvate methanol monosolvate], {[Cd(C ₁₂ H ₇ N ₂ O ₄ ) ₂ (C ₃ H ₇ NO)]·C ₃ H ₇ NO·CH ₃ OH} _n , (1), poly[[(μ ₂ -acetato-κ ² O:O′)[μ ₃ -3-nitro-4-(pyridin-4-yl)benzoato-κ ³ O:O′:N]bis[μ ₃ -3-nitro-4-(pyridin-4-yl)benzoato-κ ⁴ O,O′:O′:N]dicadmium(II)] N,N-dimethylacetamide disolvate monohydrate], {[Cd ₂ (C ₁₂ H ₇ N ₂ O ₄ ) ₃ (CH ₃ CO ₂ )]·2C ₄ H ₉ NO·H ₂ O} _n , (2), andcatena-poly[[[diaquanickel(II)]-bis[μ ₂ -3-nitro-4-(pyridin-4-yl)benzoato-κ ² O:N]] N,N-dimethylacetamide disolvate], {[Ni(C ₁₂ H ₇ N ₂ O ₄ ) ₂ (H ₂ O) ₂ ]·2C ₄ H ₉ NO} _n , (3), have been prepared. Single-crystal structure analysis shows that the Cd ^II atom in MOF (1) has a distorted pentagonal bipyramidal [CdN ₂ O ₅ ] coordination geometry. The [CdN ₂ O ₅ ] 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 [CdNO ₆ ] and a distorted octahedral [CdN ₂ O ₄ ] coordination geometry, respectively. Two Cd ^II ions are connected by three carboxylate groups to form a binuclear [Cd ₂ (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 [NiN ₂ O ₄ ] 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—HWO 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 CO ₂ /N ₂ at 273 K (i.e. the amount of CO ₂ adsorption is 71 times higher than N ₂ at the same pressure).