A Robust Metal-Organic Framework With 'Molecular Gates' for Efficient Separation of Ethane From Ethylene

Ethane-selective sorbents can enable single-step purification of ethylene but remain elusive to date. We report a Zn-based metal-organic framework (ZAI-3N) decorated with amino-based 'molecular gates' that exhibit highly selective adsorption of C₂H₆ over C₂H₄. Upon activation, ZAI-3N (zinc-adenine-3-aminoisonicotinic acid) features contractions of both Zn─N bonds and pores (from 2.009 to 1.914 Å and from 4.88 × 3.40 to 3.47 × 2.75 Ų, respectively). At 313 K and 1 bar, ZAI-3N exhibits an exceptional ratio of 10.6 for C₂H₆/C₂H₄ uptakes and a benchmark selectivity of 11.7, outperforming state-of-the-art porous solids. Synchrotron X-ray powder diffraction and modelling reveal that the methyl group in C₂H₆ can trigger amino rotation and facilitate gate opening, while π-electrons of C₂H₄ hinder such a process with a notably increased barrier (～5 and 11 kJ mol^-1, respectively). Dynamic breakthrough experiments confirm the efficient separation of C₂H₆/C₂H₄ (v/v = 5/5 and 1/9), affording C₂H₄ with a high purity of 99.4% in single step with excellent recyclability and an C₂H₄ productivity of 10.3 mL g^-1. This work demonstrates the judicious choice of 'molecular gate' as a promising protocol for challenging industrial gas separations.