Three novel MOFs constructed from 1,3,5-tris(1-imidazolyl)benzene and dicarboxylate ligands with selective adsorption for C2H2/C2H4 and C2H6/CH4

The urothermal reactions of Co(II)/Zn(II) salts with the diverse carboxylic acid and 1,3,5,-tris(1-imidazolyl)benzene(tib) ligands afforded three novel MOFs, namely, [Co₃(tib)₂(abdc)₂(ox)]₂·6H₂O (1), [Co₃O(tib)(abdc)₂(DMI)]·2DMI·2H₂O (2) and [Zn₃I₂(tib)₂(napdc)₂]·2DMI·2H₂O (3), (H₂abdc = 5-amino-1,3-benzenedicarboxylate, H₂napdc = 1,4-naphthalene dicarboxylic acid and DMI = 1,3-dimethyl-2-imidazolidinone). In compounds 1 and 2, the Co(II) atoms are connected by polycarboxylate ligands to form two-dimensional (2D) layers that are pillared by tib ligands leading to the formation of 3D porous frameworks. In compound 3, the Zn(II) atoms are linked by tib ligands to form one-dimensional ribbon-like chains which are further connected by polycarboxylate ligands, making a 3D framework possible. Compound 1 can selectively adsorb unsaturated hydrocarbon molecules (C₂H₂ and C₂H₄) and saturated hydrocarbon molecules (C₂H₆ and CH₄). Specifically, compound 1 has high IAST selectivity for acetylene and methane (0.50 : 0.50, v/v) at 273 K and 1 bar. DFT calculations reveal that the π-conjugated hexagonal carbon ring may be the primary adsorption site because there are π-π interactions between the unsaturated hydrocarbon molecules (C₂H₂ and C₂H₄) and the π-conjugated hexagonal carbon ring in the framework of compound 1.