Ligand Conformation Fixation Strategy for Expanding the Structural Diversity of Copper-Tricarboxylate Frameworks and C₂H₂ Purification Performance Studies

Structural and functional expansion of metal–organic frameworks (MOFs) is fundamentally important because it not only enriches the structural chemistry of MOFs but also facilitates the full exploration of their application potentials. In this work, by employing a dual-site functionalization strategy to lock the ligand conformation, we designed and synthesized a pair of biphenyl tricarboxylate ligands bearing dimethyl and dimethoxy groups and fabricated their corresponding framework compounds through coordination with copper(II) ions. Compared to the monofunctionalized version, introduction of two side groups can significantly fix the ligand conformation, and as a result, the dual-methoxy compound exhibited a different network structure from the mono-methoxy counterpart. Although only one almost orthogonal conformation was observed for the two ligands, their coordination framework compounds displayed distinct topological structures probably due to different solvothermal conditions. Significantly, with a hierarchical cage-type structure and good hydrostability, the dimethyl compound exhibited promising practical application value for industrially important C2H2 separation and purification, which was comprehensively demonstrated by equilibrium/dynamic adsorption measurements and the corresponding Clausius–Clapeyron/IAST/DFT theoretical analyses