Peripheral Silyl Bridging Unlocks Latent Porosity of a Nonporous Organic Cage for Moisture‐Tolerant Gas Separations

Porous organic cages (POCs) with well‐defined internal cavities are promising molecular adsorbents for gas separation. However, a majority of POCs are constructed from imine bonds and thus suffer from limited chemical and moisture stability. In contrast, many chemically robust and synthetically scalable non‐imine cages have been largely overlooked, mainly because dense molecular packing blocks access to their intrinsic cavities. Here we show that peripheral bridging can unlock the hidden porosity of a robust non‐imine cage, Noria, without redesigning the cage skeleton for moisture‐resistant gas separation. The abundant peripheral hydroxyl groups of Noria render it intrinsically hydrophilic and promote extensive intermolecular hydrogen‐bonding‐induced dense packing, resulting in inaccessible cavities. Covalent silyl bridging eliminates these interactions and converts nonporous hydrophilic Noria into porous hydrophobic NoriaSi. The resulting porous NoriaSi crystals (NoriaSi α ) are highly robust and contain gas‐accessible dumbbell‐shaped nonpolar pockets for size‐dependent adsorption trends across light hydrocarbons, olefins, and noble gases. As such, NoriaSi α as a single hydrophobic sorbent enables three representative gas separations, including natural gas upgrading, olefin purification, and Xe/Kr separation under both ambient and fully humid conditions, with performance comparable to or exceeding that of most reported molecular adsorbents. Combined with scalable synthesis, crystalline stability, low water affinity, and separation performance, this work establishes peripheral bridging as an effective strategy for unlocking the hidden cavities in Noria into moisture‐resistant porous NoriaSi α for practical gas separation.