Nanoporous Cu(II)-Adenine-Based Metal–Organic Frameworks for Selective Adsorption of C2H2 from C2H4 and CO2

In some important chemical processes, selective removal of C2H2 from other gases is necessary. The method of selecting porous materials for separation is energy-efficient and economical in comparison with some traditional methods, such as solvent extraction and low-temperature distillation. Herein, we present three nanoporous Cu(II)-adenine-based metal–organic frameworks (MOFs), [Cu(AD)(AC)], [Cu2(AD)2(SA)], and [Cu2(AD)2(GA)], denoted as Cu-AD-AC, Cu-AD-SA, and Cu-AD-GA, respectively (HAD = adenine, HAC = acetic acid, H2SA = succinic acid, and H2GA = glutaric acid). The adenine ligands and secondary aliphatic acid ligands of these MOFs are easy-accessible. The MOFs show isomorphic three-dimensional (3D) microporous framework structures with slightly different pore microenvironments due to the presence of different aliphatic acid ligands. There are 1D channels of ∼4.5 to ∼5 Å diameter in the MOFs, the surfaces of which are decorated with a Lewis basic site. The subtle structural differences lead to large differences in the stability and porosity of the MOFs. Among them, Cu-AD-SA showed a relatively high adsorption capacity of C2H2. In addition, adsorption isotherm measurements for single-component gases and breakthrough experiments for binary gas mixtures suggested that Cu-AD-SA could selectively adsorb C2H2 from a C2H2/C2H4 or a C2H2/CO2 mixture.