Cavity-induced spin-spin interaction between organic radicals within a self-assembled coordination cage.

We present a new approach for manipulating spin-spin interaction by the self-assembled M6L4-coordination cage. Stable radicals are encapsulated by the cage to become a radical pair in triplet state in both solid and solution states, although the radicals themselves show doublet character without particular intermolecular interaction in solution. These results were confirmed by ESR spectroscopy and X-ray crystallography.