Angle-Dependent Assembly of Cu(II)-Based Paddle-Wheel Clusters into 1D Porous Coordination Polymers Toward Adsorptive C2H2/CO2 Separation

Abstract

Three one-dimensional porous coordination polymers (PCPs) based on Cu2(OAc)4 paddle-wheel clusters were synthesized by using pyridyl ligands with distinct coordination geometries, including linear 1,4-di(4-pyridyl)benzene (DPB) and bent triazole-based ligands 3,5-bis(4-pyridyl)-1,2,4-triazole (HBPT) and 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole (HABPT). Single-crystal X-ray diffraction (SCXRD) reveals that all three compounds share a common [Cu2(OAc)4(L)] stoichiometry and paddle-wheel motif but assemble into different chain conformations and three-dimensional packings depending on ligand geometry and torsional flexibility. Gas adsorption measurements combined with PXRD analyses indicate irreversible densification of the DPB-based PCP upon desolvation, resulting in negligible accessible porosity. In contrast, the HABPT-based analogue exhibits suppressed gas uptake despite retaining crystallinity, suggesting vacuum-induced framework contraction. Among them, the HBPT-based analogue retains permanent porosity and exhibits a moderate thermodynamic preference for C2H2 over CO2, as supported by adsorption measurements, Qst analysis, IAST calculations, and molecular simulations.