Integration of Open Metal Sites and Lewis Basic Sites for Construction of a Cu MOF with a Rare Chiral Oh‐type cage for high performance in methane purification.

Abstract: A Cu metal‐organic framework (MOF), [Cu₄(PMTD)₂(H₂O)₃]⋅20 H₂O, 1, (where PMTD is 1,4‐phenylenebis(5‐methyl‐4H‐1,2,4‐triazole‐3,4‐diyl)bis(5‐carboxylato‐3,1‐phenylene)bis(hydroperoxymethanide)), with a rare chiral O_h‐type cage, and dual functionalities of open metal sites and Lewis basic sites, based on a designed U‐shaped ligand, was synthesized by hydrothermal methods. It exhibits high CO₂, C₂, and C₃ hydrocarbon storage capacity under atmospheric pressure, as well as high H₂ (1.96 wt.%) adsorption capacity at 77 K. Methane purification capacity was tested and verified step by step. Isosteric heats (Q_st) studies reveal that CH₄ has the weakest van der Waals host–guest interactions among the seven gases at 298 K. Ideal adsorbed solution theory (IAST) calculation reveals that compound 1 is more selective toward CO₂, C₂H₆, and C₃H₈ over CH₄ in further calculating its separation capacity, as exemplified for CO₂/CH₄ (50:50, 5:95), C₂H₆/CH₄ (50:50, 5:95), or C₃H₈/CH₄ (50:50, 5:95) binary gas mixtures. Breakthrough experiments show that 1 has a significantly higher adsorption capacity for CO₂, C₂H₆, and C₃H₈ than CH₄. The selective adsorption properties of 1 make it a promising candidate for methane purification. [ABSTRACT FROM AUTHOR]