Synthesis, Characterization, and Adsorption Studies of Nickel(II), Zinc(II), and Magnesium(II) Coordination Frameworks of BTTB

Three porous metal–organic frameworks {[Ni­(H₂BTTB)·(H₂O)₂]·(DIOX)₂}_n (1), {[Zn­(H₂BTTB)]·(DEF)₃·(H₂O)₂}_n (2), and {[Mg­(H₂BTTB)·(C₂H₅OH)₂]·(DEF)₄}_n (3) based on the 4,4′,4″,4‴-benzene-1,2,4,5-tetrayltetrabenzoic acid (H₄BTTB) ligand have been synthesized under solvothermal conditions (DIOX = dioxane). These three MOFs show structural diversities: compound 1 is a two-dimensional (2D) grid layer, compound 2 is a 2-fold interpenetrated 3D framework with a pillared-layer structure, and compound 3 is a noninterpenetrated 3D framework with a (4, 4)-connected binodal net. Compound 1 and compound 2 have BET surface areas of 391 and 447 m²/g, respectively; however, the surface area of compound 3 cannot be experimentally determined. All three MOFs have a higher adsorption preference for CO₂ over N₂ and CH₄. Ideal adsorbed solution theory was used to estimate binary adsorption selectivities. Compound 2 shows the highest capacity for all three gases, whereas compound 1 shows the highest selectivity for CO₂ over CH₄ and N₂. Compound 1 exhibits a selectivity of ∼30 for CO₂ over N₂ in equimolar mixtures.