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

ABSTRACT 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.