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.