Crystal Engineering of Chelating Hybrid Ultramicroporous Materials via Pillar Modulation for Energy‐Efficient Acetylene Separation

Acetylene, C 2 H 2, a commodity chemical, is a building block for producing plastics, synthetic rubbers, and pharmaceuticals. Among emerging classes of recyclable adsorbents, hybrid ultramicroporous materials (HUMs) demonstrate C 2 H 2 ‐selective physisorption, yet their C 2 H 2 over CO 2 (C 2 H 2 /CO 2 ) separation performances are often constrained by trade‐offs between uptake capacity, selectivity, ease in regeneration, and stability under humid conditions. Expanding upon the prototypal chelating ligand N 1 , N 2 ‐bis(pyridine‐4‐ylmethyl)ethane‐1,2‐diamine (enmepy)‐derived HUM family [Zn(enmepy)(MF 6 )] n , MFSIX‐enmepy‐Zn , through systematic pillar modulation, three previously unreported HUMs are isolated as single crystals. [Zn(enmepy)(SnF 6 )] n , SNIFSIX‐enmepy‐Zn , offers limited stability, whereas [Zn(enmepy)(TiF 6 )] n , TIFSIX‐enmepy‐Zn , and [Zn(enmepy)(NbOF 5 )] n , NbOFFIVE‐enmepy‐Zn are more robust. Gas sorption isotherms, sorption kinetics, dynamic column breakthrough experiments, and molecular modelling identify NbOFFIVE‐enmepy‐Zn as offering a combination of high C 2 H 2 /CO 2 selectivity (>5) with low regeneration energy requirements (≈31 kJ mol − 1 ) and superior hydrolytic stability (>7 days, 75% relative humidity). Further, NbOFFIVE‐enmepy‐Zn delivers effective C 2 H 2 /CO 2 separation (a separation factor > 5) under both dry and humid conditions, underscoring the importance of fine‐tuning inorganic pillars in balancing adsorption performance and material robustness.