Enantioselective Recognition and Separation by a Homochiral Porous Lamellar Solid Based on Unsymmetrical Schiff Base Metal Complexes

A homochiral lamellar supramolecular host system has been developed by treating 3-[(E)-{[(1R,2R)-2-aminocyclohexyl]imino}methyl]-4-hydroxybenzoic acid (H2L) with copper nitrate and characterized by a variety of techniques including microanalysis, IR spectroscopy, thermogravimetric analysis (TGA), circular dichroism (CD) spectroscopy, and powder and single-crystal X-ray diffraction. Tridentate Schiff base L ligands link adjacent metal centers to form ID coordination polymeric chains using tridentate N2O donors and carboxylate groups, while interchain metal-oxygen and hydrogen-bonding interactions further link 1D polymeric chains to a porous lamellar solid. The host features a flexible helical framework for guest inclusions and chiral amphiphilic channel surfaces lined with amine hydrogen atoms and aliphatic groups capable of multiple interactions with guest species. It allows for the development of an efficient approach for highly enantioselective separation of racemic secondary alcohols by inclusion crystallization followed by distillation (> 99.5% ee). In addition, the host including different alcohols exhibits guest-responsive ferroelectric behavior.