Rational construction of an <i>ssa</i>-type of MOF through pre-organizing the ligand's conformation and its exceptional gas adsorption properties

Abstract

Ssa-type MOFs constructed from dicopper paddlewheels and bent diisophthalate ligands exhibit a promising potential for gas adsorption which benefits from their rich open copper sites and polyhedron-based cages with suitable sizes. However, the rational construction of such types of MOFs is exceedingly challenging because the bent diisophthalate ligands employed are inclined to exhibit various conformations and thus are prone to form MOFs with varied topologies. In this work, by pre-organizing the ligand's conformation, we successfully targeted an ssa-type MOF ZJNU-57 from a bent diisophthalate ligand. More significantly, ZJNU-57 exhibits excellent hydrolytic stability and high C₂H₂ and CO₂ uptake capacities as well as impressive C₂H₂/CH₄ and CO₂/CH₄ adsorption selectivities, indicating its promising potential for C₂H₂/CH₄ and CO₂/CH₄ separation, which are relevant to acetylene production and natural gas purification. This work not only provides a rare water-stable MOF based on the Cu₂(COO)₄ cluster for highly selective adsorption of C₂H₂ and CO₂ from CH₄, but also demonstrates that the ligand conformation-controlled assembly strategy may be an efficient approach toward the construction of MOF materials with definite topologies for specific applications.