Buckyball Difluoride F 2 − @C 60 + —A Single‐Molecule Crystal

We report the F 2 @C 60 system as the first example of an endohedral fullerene in which C 60 acts as a cation C 60 + interacting with endohedral anion, F 2 − . Our state‐of‐the‐art computations reveal that in F 2 @C 60 , despite of the known high electron affinity of C 60 , an electron is transferred from C 60 to F 2 resulting in the F 2 − @C 60 + system. The F−F bond length in F 2 @C 60 is substantially longer than in free F 2 , which is the result of electron‐transfer to the antibonding σ u molecular orbital of F 2 . Interestingly, although there is a full charge‐transfer of one electron between C 60 and F 2 , only negligible delocalized covalent interactions are found between F 2 − and C 60 + which is a reminiscent of ionic crystals. Therefore, F 2 − @C 60 + can be considered as a single‐molecule crystal. The other encapsulated halogens in C 60 do not show such behavior.