Fully Inverse Adsorption Enables One-Step High-Purity C₂H₂ Separation from Ternary C₂ Mixtures in a Robust Porous Crystal

Directly harvesting ultrahigh-purity acetylene (C₂H₂) from ternary C2 mixtures remains a significant challenge due to the intrinsic adsorption trend of conventional porous materials (C₂H₂ &gt; ethylene (C₂H₄) &gt; ethane (C₂H₆)). To overcome this, we propose an adsorption-steering strategy that exploits steric pore-environment engineering in microporous crystals. By using the pyrazole carboxylate ligand functionalized with trifluoromethyl/methyl groups, we developed a series of MOF-5 analogs with robust structures and finely-tuned pores. One of them, named<b> NTU-98,</b> featuring dual cages (~5.6 and 10.4 Å in pore size), fully reverses the adsorption trend of C2 hydrocarbons (C₂H₆ &gt; C₂H₄ &gt; C₂H₂), enabling direct production of ultrahigh-purity C₂H₂ (&gt;99.99%) from ternary feeds at room temperature, in one step. Density functional theory calculations and gas-loaded crystallographic analyses reveal that the methyl groups strategically positioned within both cages synergistically enhance host-guest interactions with the more saturated C₂H₄ and C₂H₆, while concurrently weaken the affinity for the more polarizable C₂H₂. This work not only presents the first porous crystal capable of directly purifying C₂H₂ from ternary C2 feeds, but also offers a generalizable blueprint for engineering microporous environments for challenging gas separations.