Adaptive Throat‐Sieving Gate in a Metal Azolate Framework Enabling Synergistic Equilibrium‐Kinetic Separation of Propylene and Propane

Developing porous adsorbents for propylene/propane (C 3 H 6 /C 3 H 8 ) separation faces the challenge of integrating high adsorption capacity with fast adsorption kinetics. Herein, we address this challenge through precise pore control in a slightly flexible metal azolate framework NUM‐27a, enabling synergistic equilibrium‐kinetic separation of C 3 H 6 /C 3 H 8 . The periodically expanded throat gate enables effective impeding the diffusion of C 3 H 8 , while a large pocket‐shaped cavity decorated with exposed oxide groups facilitates exceptional C 3 H 6 capture at low pressures. Specifically, NUM‐27a achieves exceptional low‐pressure C 3 H 6 capture (89.61 cm 3 cm −3 at 0.1 bar) and a record C 3 H 6 packing density (310.0 g L −1 at 0.01 bar). Kinetic analysis further reveals effective diffusion coefficient for C 3 H 6 is 1.57 × 10 −4 s −1 at 298 K. Gas‐loaded single crystal X‐ray diffraction analysis coupled with computational simulations elucidate that the intrinsic pore geometry underpins the unique adsorption and separation performance. Breakthrough experiments validate the outstanding separation performance of NUM‐27a for C 3 H 6 /C 3 H 8 mixtures. Moreover, the great stability, recyclability, and low‐cost precursors of NUM‐27a underline its potential as a reliable adsorbent for C 3 H 6 /C 3 H 8 separation. The work unveils the adaptive throat‐sieving gate strategy with optimal separation performance for challenging gas separations.