Stable Ultramicroporous Metal–Organic Framework with Hydrophilic and Hydrophobic Domains for Selective Gas Adsorption

Abstract Herein, we report the thermal and chemical stability, and the gas adsorption behavior, of a mixed‐linker phosphonate MOF, [Cu(4,4′‐bpy) 0.5 (1,4‐NDPAH 2 )], namely TUB41 (where bpy = bipyridine and NDPAH 4 = naphthalenediphosphonic acid). TUB41 demonstrates remarkable chemical stability across a wide pH range (1–11) and retains its structural integrity after 2 years of repeated adsorption cycles and activation at 80 °C under ambient humidity. Cryogenic adsorption experiments reveal that TUB41's pores selectively exclude gases with larger kinetic diameters, such as N 2 and Ar, while accommodating smaller molecules like CO 2 and H 2 O at elevated temperatures. The enthalpies of adsorption for CO 2 at a loading 0.01 mmol g −1 and H 2 O at a loading of 0.7 mmol g −1 are −41 and −38 kJ mol −1 , respectively, reflecting their strongly attractive interactions with TUB41 under different conditions. Molecular dynamics simulations reveal that CO 2 molecules adopt ordered arrangements in the central hydrophobic regions of the pores, guided by strong nonbonding interactions, while H 2 O molecules preferentially bind to the hydrophilic secondary building units. Mean‐squared displacement analyses confirm that both gases remain spatially constrained within the pores. These findings highlight TUB41 as a chemically robust and highly selective MOF, with potential for applications in gas separation, photocatalytic water splitting, and CO 2 reduction under challenging conditions.