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 (TDM8–) has been used to connect a dicopper paddlewheel building unit affording a metal–organic framework (MOF), Cu4(H2O)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 N2, Ar, and H2 on an activated PCN-26 at 77 K, 1 bar, reveals a Langmuir surface area of 2545 m2/g, a Brunauer–Emmett–Teller (BET) surface area of 1854 m2/g, a total pore volume of 0.84 cm3/g, and a H2 uptake capacity of 2.57 wt %. Additionally, PCN-26 exhibits a CO2/N2 selectivity of 49:1 and CO2/CH4 selectivity of 8.4:1 at 273 K. To investigate properties of gas adsorption and the adsorption sites for CO2 in activated PCN-26, theoretical simulations of the adsorption isotherms of CO2, CH4, and N2 at different temperatures were carried out. Experimental results corroborate very well with those of molecular simulations.