An anionic metal–organic framework constructed from a triazole-functionalized diisophthalate featuring hierarchical cages for selective adsorptive C2H2/CH4 and CO2/CH4 separation

Abstract

Exploring organic linkers is very important to target porous metal–organic frameworks with desired structures and properties. In this work, we devised a triazole-functionalized bent diisophthalate ligand, 5,5′-(triazole-2,5-diyl) diisophthalate (H₄L), which was used to successfully construct an anionic copper-based MOF ([Cu₆(L)₃(H₂O)₄(HCOO)]·Me₂NH₂⁺·20DMF) under solvothermal reaction conditions. Single-crystal X-ray diffraction analyses reveal that the title MOF compound features three types of polyhedral cages with different shapes and sizes. More importantly, the title MOF compound after desolvation exhibits promising potential for industrially important C₂H₂/CH₄ and CO₂/CH₄ separations. At 298 K and 1 atm, the C₂H₂ and CO₂ uptakes reach 107.6 and 65.6 cm³ (STP) g⁻¹, respectively. The adsorption selectivities are predicted to be 33.4–120.3 for an equimolar C₂H₂–CH₄ gas mixture and 6.4–7.6 for an equimolar CO₂–CH₄ gas mixture at 298 K and pressures varying from 1 to 109 kPa. The highly selective adsorption of C₂H₂ and CO₂ over CH₄ might be attributed to the synergistic interplay between suitable pore sizes, functional active sites, such as open metal sites and Lewis basic nitrogen atoms in the pore surface, and the ionic nature of the framework.