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.