Highly stable chiral Cr(iii)-based metal–organic frameworks for enantioadsorption separation of aromatic alcohols

Abstract

Homochiral Cr(III)-based metal–organic frameworks (Cr-HMOFs) are competitive and attractive for chiral materials due to their robustness and ultra-high surface areas. However, extremely limited strategies for the synthesis of Cr-HMOFs and the types of chiral ligands available have hindered the development of novel Cr-HMOFs. Recently, the solvent-assisted metal metathesis (SAMM) strategy is expected to be used in the design and synthesis of Cr-HMOFs. Herein, two L-amino acid-functionalized Cr-HMOFs, Cr-HMOF-1 and Cr-HMOF-2, were prepared from unstable Fe-HMOFs Fe-HMOF-1 and Fe-HMOF-2 through the SAMM strategy. These are the first Cr-HMOFs reported to date, being directly synthesized using enantiomerically pure chiral ligands and stable in water over a wide pH range. Besides, chiral amino acid moieties are periodically aligned within the large cubic cages and 1D channels of the frameworks, facilitating stereoselective recognition of guest molecules via supramolecular interactions. The results showed that Cr-HMOF-1 and Cr-HMOF-2 exhibited excellent enantioselective separation ability for racemic aromatic alcohols. In particular, the ee values for the separation of 1-phenylethanol by Cr-HMOF-1 and Cr-HMOF-2 are as high as 86.8 and 98.6%, respectively, which are relatively high among the reported HMOFs. This study provides a new design approach for the preparation of robust Cr-HMOFs with novel topologies and functionalization.