Crystallographic Evidence for Direct Metal-Metal Bonding in a Stable Open-Shell La2@Ih-C80 Derivative

Endohedral metallofullerenes (EMFs) have novel structures and properties that are closely associated with the internal metallic species. Benzyl radical additions have been previously shown to form closed-shell adducts by attaching an odd number of addends to open-shell EMFs (such as Sc3C2@I-h-C-80) whereas an even number of groups are added to closed-shell EMFs (for example Sc3N@I-h-C-80). Herein we report that benzyl radical addition to the closed-shell La-2@I-h-C-80 forms a stable, open-shell monoadduct instead of the anticipated closed-shell bisadduct. Single-crystal X-ray diffraction results show the formation of a stable radical species. In this species, the La-La distance is comparable to the theoretical value of a La-La covalent bond and is shorter than reported values for other La-2@I-h-C-80 derivatives, providing unambiguous evidence for the formation of direct La-La bond.