Low-symmetry coordination cages enable recognition specificity and selective enrichment of higher fullerene isomers

Abstract

The discovery of buckminsterfullerene (C60) marked a milestone in exploring three-dimensional carbon materials. However, with the exponential increase in the number of isomers for higher fullerenes, it has become challenging to realize the enrichment of the isomers by molecular recognition. Here we report two pseudo-cubic metal–organic cages, T and S4, with distinct cavity microenvironments, that showcase recognition specificity towards higher fullerene isomers. Compared with cage T, a symmetry shift from S4 to C2 emerges upon encapsulating an ellipsoidal D2-C76 guest, owing to the precise shape matching that curtails guest rotation. Furthermore, the low-symmetry cage S4 shows exceptional sensitivity in distinguishing between closely related isomers, such as a pair of C2v-symmetric C78 isomers, and shows promise for the selective enrichment of higher fullerenes. The approach of reducing symmetry positions metal–organic cages as promising candidates for encapsulating and identifying a broader spectrum of fullerene isomers, paralleling the specificity observed in biological systems. Symmetry reduction from T to S4 in coordination cages enables selective recognition of higher fullerene isomers, including D2-C76, C2v(2)-C78 and C2v(3)-C78, presenting a promising approach for fullerene identification and enrichment.