Ultrastable Copper Carboxylate Metal–Organic Frameworks

Abstract

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.