Sponge-like molecular cage for purification of fullerenes

Since fullerenes are available in macroscopic quantities from fullerene soot, large efforts have been geared toward designing efficient strategies to obtain highly pure fullerenes, which can be subsequently applied in multiple research fields. Here we present a supramolecular nanocage synthesized by metal-directed self-assembly, which encapsulates fullerenes of different sizes. Direct experimental evidence is provided for the 1: 1 encapsulation of C-60, C-70, C-76, C-78 and C-84, and solid state structures for the host-guest adducts with C-60 and C-70 have been obtained using X-ray synchrotron radiation. Furthermore, we design a washing-based strategy to exclusively extract pure C-60 from a solid sample of cage charged with a mixture of fullerenes. These results showcase an attractive methodology to selectively extract C-60 from fullerene mixtures, providing a platform to design tuned cages for selective extraction of higher fullerenes. The solid-phase fullerene encapsulation and liberation represent a twist in host-guest chemistry for molecular nanocage structures.