Overlapping-ligand strategy in copper-paddlewheel supramolecular isomers for enhanced stability and efficient C2H2/CO2 separation

Abstract

Metal-organic frameworks (MOFs) have shown fascinating application prospects in gas storage and separation over the past two decades. However, integrating MOFs with high stability and efficient gas separation performance remains a great challenge, especially for the MOFs bearing open metal sites. Herein, we present an overlapping-ligand strategy to construct stable MOFs for highly efficient C₂H₂ / CO₂ separation. A pair of supramolecular isomers, i.e. FJI-W8-A and FJI-W8-B, has been successfully synthesized based on copper paddlewheels and carboxylic acid ligands. The phenomenon of supramolecular isomerism mainly arises from the difference in the conformation of the ligand during the assembly process. In FJI-W8-A, the ligand adopts an overlapping assembly mode, whereas in FJI-W8-B the ligand is not stacked. Consequently, FJI-W8-A exhibits significantly enhanced stability compared with FJI-W8-B, maintaining its crystalline structure and porosity even being exposed in water. Benefiting from the combined features of good stability, high porosity and abundant open metal sites, FJI-W8-A shows excellent performance in C₂H₂ / CO₂ separation even under humid conditions, which has been demonstrated by the practical breakthrough experiments.