Ca@C82 isomers: Computed temperature dependency of relative concentrations

Isolation and structural characterization of two very large, and largely empty, endohedral fullerenes: Tm@C(3v)-C(94) and Ca@C(3v)-C(94)

The structures of two newly synthesized endohedral fullerenes, Tm@C(3v)-C(94) and Ca@C(3v)-C(94), have been determined by single crystal X-ray diffraction on samples cocrystallized with Ni(II)(octaethylporphyrin). Both compounds exhibit the same cage geometry and conform to the isolated pentagon rule (IPR). The metal ions within these rather large cages are localized near one end and along the C(3) axis. While the calcium ion is situated over a C-C bond at a 6:6 ring junction, the thulium ion is positioned above a six-membered ring of the fullerene.

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

Metal-atom migration outside from a defective fullerene cage of a metallofullerene Gd@C(82) (Ca@C(82)), where the Gd(3+) (Ca(2+)) ion is incorporated inside the C(2)(v)()-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 Gd(3)(+)() 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 Ca(2+) 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.