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The quest for understanding the structure-property correlation in porous materials has remained a persistent focus across various research domains, particularly within the sorption realm. Molecular metal oxide clusters, owing to their precisely tunable atomic structures and long-range order, exhibit significant potential as versatile platforms for sorption investigations. This study presents a series of isostructural Ti8Ce2-oxo clusters with subtle variations in coordinated linkers and explores their gas sorption behavior. Notably, Ti8Ce2-BA (where BA denotes benzoic acid) manifests a distinctive twostep profile during CO2 adsorption, accompanied by a hysteresis loop. This observation marks a pioneering instance within the metal oxide cluster field. Of particular intrigue, the presence of unsaturated Ce(Ⅳ) sites was found to be correlated with the stepped sorption property. Moreover, the introduction of an electrophilic fluorine atom, positioned ortho or para to the benzoic acid, facilitated precise control over gate pressure and stepped sorption quantities. Advanced in-situ techniques systematically unraveled the underlying mechanism behind this unique sorption behavior. The findings elucidate that robust Lewis base-acid interactions are established between CO2 molecules and Ce ions, consequently altering the conformation of coordinated linkers. Conversely, the F atoms primarily contribute to gate pressure variation by influencing the Lewis acidity of the Ce sites. This research advances the understanding in fabricating geometrically "flexible" metal-oxo clusters and provides profound insights into their host-guest interaction motifs. These insights hold substantial promise across diverse fields, particularly in CO2 gas capture and gas-phase catalysis, and offer valuable guidance for future adsorbent designs grounded in fundamental theories of structure-property relationships. 

Abstract Flexible metal–organic materials that exhibit stimulus-responsive switching between closed (non-porous) and open (porous) structures induced by gas molecules are of potential utility in gas storage and separation. Such behaviour is currently limited to a few dozen physisorbents that typically switch through a breathing mechanism requiring structural contortions. Here we show a clathrate (non-porous) coordination network that undergoes gas-induced switching between multiple non-porous phases through transient porosity, which involves the diffusion of guests between discrete voids through intra-network distortions. This material is synthesized as a clathrate phase with solvent-filled cavities; evacuation affords a single-crystal to single-crystal transformation to a phase with smaller cavities. At 298 K, carbon dioxide, acetylene, ethylene and ethane induce reversible switching between guest-free and gas-loaded clathrate phases. For carbon dioxide and acetylene at cryogenic temperatures, phases showing progressively higher loadings were observed and characterized using in situ X-ray diffraction, and the mechanism of diffusion was computationally elucidated.