Ultrastable Copper Carboxylate Metal–Organic Frameworks

Direct synthesis of acid-base-stable copper carboxylate metal-organic frameworks (MOFs) is of great significance but faces substantial challenges. Herein, a nanoenvelope strategy was proposed to protect the copper paddle-wheel cluster in the assembly between Cu(II) and 4,4',4″,4‴-(1,3,6,8-pyrenetetrayl)tetrakis-benzoic acid (H4TBAPy) through AB stacking. This structure unexpectedly restricted the access of water to the Cu-O bonds, creating one of the most stable MOFs in water (240 days, RT) as well as in acid and base solutions (pH from 0 to 13). Water vapor adsorption experiments, density functional theory (DFT) calculations, and radial distribution function (RDF) analyses further confirmed the high water resistance of Cu2TBAPy. Moreover, excellent separation for xylene isomers was achieved, with a resolution of 18.2 (meta-xylene/para-xylene) and a durability of 31 months, which surpassed all previous materials. Xylene isomer impurities were separated with a detection limit as low as 1.33 pg. The remarkable stability of Cu2TBAPy offers valuable guidance for the design and synthesis of highly water-stable copper carboxylate MOFs.