Single-crystal-to-single-crystal intercalation of a low-bandgap superatomic crystal

The controlled introduction of impurities into the crystal lattice of solid-state compounds is a cornerstone of materials science. Intercalation, the insertion of guest atoms, ions or molecules between the atomic layers of a host structure, can produce novel electronic, magnetic and optical properties in many materials. Here we describe an intercalation compound in which the host [Co₆Te₈(PⁿPr₃)₆][C₆₀]₃, formed from the binary assembly of atomically precise molecular clusters, is a superatomic analogue of traditional layered atomic compounds. We find that tetracyanoethylene (TCNE) can be inserted into the superstructure through a single-crystal-to-single-crystal transformation. Using electronic absorption spectroscopy, electrical transport measurements and electronic structure calculations, we demonstrate that the intercalation is driven by the exchange of charge between the host [Co₆Te₈(PⁿPr₃)₆][C₆₀]₃ and the intercalant TCNE. These results show that intercalation is a powerful approach to manipulate the material properties of superatomic crystals.