Superficial Chiral Etching on Achiral Metal-Organic Framework for Enantioselective Sorption.

Chiral recognition and separation is of general research interests in natural product separation and the pharmacy industry. In this work, we develop a novel strategy to modify achiral porous metal-organic framework (MOF) surfaces via a superficial chiral etching process (SCEP), in which reacting a presynthesized achiral MOF with a chiral ligand produces an achiral@chiral MOF core-shell hybrid composition. SCEP creates chiral species on an achiral porous MOF surface but does not change the porosity and pore structure, enabling core-shell composition enantioselective sorption. Reacting (+)-camphoric acid, (+)-Cam, and 1,4-diazabicyclo[2.2.2]octane (Dabco) with [Cu(Btc)] microcrystals leads to a chiral MOF of [Cu((+)-Cam)Dabco] crystallites attached on the surface of [Cu(Btc)] (Btc = 1,3,5-benzenetricarboxylate). The resulting [Cu(Btc)]@[Cu((+)-Cam)Dabco] core-shell composition displays preferred sorption kinetics toward (S)-limonene against (R)-limonene, with a similar discrimination effect with pure chiral [Cu((+)-Cam)Dabco]. Superficial chiral etching of the porous achiral MOF represents an economic and efficient strategy for enantioselective separation.