Robust Metal–Organic Framework with An Octatopic Ligand for Gas Adsorption and Separation: Combined Characterization by Experiments and Molecular Simulation

A newly designed octatopic carboxylate ligand, tetrakis[(3,5-dicarboxyphenyl)oxamethyl]methane (TDM 8– ) has been used to connect a dicopper paddlewheel building unit affording a metal–organic framework (MOF), Cu 4 (H 2 O) 4 (TDM)· xS (PCN-26· xS, S represents noncoordinated solvent molecules, PCN = porous coordination network) with novel structure, high gas uptake, and interesting gas adsorption selectivity. PCN-26 contains two different types of cages, octahedral and cuboctahedral, to form a polyhedron-stacked three-dimensional framework with open channels in three orthogonal directions. Gas adsorption studies of N 2, Ar, and H 2 on an activated PCN-26 at 77 K, 1 bar, reveals a Langmuir surface area of 2545 m 2 /g, a Brunauer–Emmett–Teller (BET) surface area of 1854 m 2 /g, a total pore volume of 0.84 cm 3 /g, and a H 2 uptake capacity of 2.57 wt %. Additionally, PCN-26 exhibits a CO 2 /N 2 selectivity of 49:1 and CO 2 /CH 4 selectivity of 8.4:1 at 273 K. To investigate properties of gas adsorption and the adsorption sites for CO 2 in activated PCN-26, theoretical simulations of the adsorption isotherms of CO 2, CH 4, and N 2 at different temperatures were carried out. Experimental results corroborate very well with those of molecular simulations.