Optimizing HostGuest Interaction Sites in Metal-Organic Frameworks for Benchmark One-Step Ethylene Purification.

Purifying ethylene from ternary acetylene/ethylene/ethane (C₂H₂/C₂H₄/C₂H₆) mixture in one-step requires preferential adsorption for C₂H₂ and C₂H₆, which is challenging due to the intermediate physicochemical property of C₂H₄. To address this problem, a synergistic host-guest interaction strategy is proposed for metal-organic frameworks (MOFs) by taking open metal site (OMS) to preferentially bind with electron-rich C₂H₂ through π-coordination interaction, while saturated hydrocarbon C₂H₆ primarily adsorbed via C-H∙∙∙π interactions with aromatic rings (AR). The feasibility of this strategy was demonstrated by three conformational isomeric 8-connected [Fe₃(µ₃-O)(COO)₆] trigonal prismatic trinuclear cluster-based robust MOFs (denoted as SNNU-705-α/β/γ regulated by amino groups). Combining one unoccupied OMS site and occupying AR groups in SNNU-705-α/β/γ boosts the C₂H₂ and C₂H₆ affinity and binds C₂H₄ the weakest. Aided by amino Lewis basic sites (LBSs) furtherly, SNNU-705-γ exhibits the highest C₂H₆ uptake at 298 K and 1 atm (6.13 mmol g⁻¹) among all reported MOFs for one-step C₂H₄ purification. Breakthrough experiments indicate that all SNNU-705-α/β/γ can separate C₂H₄ from C₂H₂/C₂H₄/C₂H₆ mixture in one-step with exceptional productivity (purity > 99.9999%) of 7.07, 6.75, and 5.46 mmol g⁻¹, far surpassing all adsorbents reported so far. In situ FT-IR spectra and DFT calculation validates this strategy and indicate their potential in industry applications.