Gate effect of vacancy-type defect of fullerene cages on metal-atom migrations in metallofullerenes

摘要

Metal-atom migration outside from a defective fullerene cage of a metallofullerene Gd@C-82 (Ca@C-82), where the Gd3+ (Ca2+) ion is incorporated inside the C-2v - C-82 cage, is discussed in detail at the B3LYP DFT level of theory. The metal-atom migrations are initiated by the formation of vacancy-type defects involving two coordinatively unsaturated C atoms. This step, which is assumed to proceed due to energy-particle irradiation, leads to the formation of antibonding orbitals between the two C atoms. Since the antibonding orbitals can interact with vacant d-orbitals of the Gd3+ ion in an in-phase fashion, the attractive interactions allow the Gd ion to insert into the two C atoms in the defect. As a result, the metal ion passes through the defect under energy-particle irradiation. In contrast, the Ca2+ ion with the vacant s-orbitals does not have such orbital interactions, and thus, a C - C bond is reformed between the two C atoms, which prohibits the Ca ion from penetrating the defected C-82 cage. DFT calculations nicely demonstrate that the orbital interactions control metal-atom migration around the defect site using their orbital symmetries, and therefore, the vacancy-type defect acts as a "gate" that permits a specific atom to go out from a defected fullerene cage.