Metallo-Supramolecular Octahedral Cages with Three Types of Chirality towards Spontaneous Resolution.

ABSTRACT

Chirality is one of the most important intrinsic properties of (supra)molecules. In this study, we obtained enantiomeric metallo-supramolecular octahedra without using any chiral sources. Such cages were self-assembled by prochiral trispyridine ligand L based on a C3h truxene core and CuII salts. Crystallization of the cages with BF4 - as counterions afforded racemate crystals; while crystallizations of cages with ClO4 - and OTf- as counterions resulted in conglomerates with spontaneous resolution. Three types of chirality were observed in each cage, including planar chirality of the truxene core, axial chirality from the pyridyl and truxene moieties, and propeller chirality of the pyridyl-CuII coordination sites. The cages reported here are among the largest discrete synthetic metallo-supramolecules ever reported with chiral self-sorting behavior. Remarkably, the chiral cages exhibited very slow racemization even at low concentrations, suggesting their high stability in solution.