Metallofullerenes: Their formation and characterization

Endohedral metallofullerenes are novel forms of fullerene-related materials which encage metal atom(s) in a various size of fullerene cages. Ln the present article, recent: advances on the production, separation (isolation) and various spectroscopic characterization of endohedral metallofullerenes are presented in an effort to clarify their structural and electronic properties. Endohedral metallofullerenes are produced by the DC are-discharge method with metal/graphite composite rods as positive electrodes. The endohedral metallofullerenes, such as Y@C-82, Sc@C-82, SC2@C-84 and SC3@C-82, have been purified and isolated by using the two-stage high performance liquid chromatography (HPLC). By using the purified metallofullerene samples, spectroscopic and structural features of the endohedral metallofullerenes are investigated. The ESR hyperfine splittings observed in the paramagnetic metallofullerenes such as Y@C-82, SC@C-82 and Sc3@C-82 can provide us information on electron transfer nature from the encaged metal atoms to the C-82 fullerene cage. Direct STM imaging of the metallofullerenes on clean surfaces in an ultrahigh vacuum environment shows that the endohedral metallofullerenes are stacked as close-packed arrays on the clean surfaces that uniform fee (111) faces can be grown. Synchrotron X-ray diffraction study of Y@C-82 can give us a direct structural evidence that the yttrium atom is encapsulated within the C-82 cage. It shows that the encaged yttrium atom is not in the center of the cage but very close to the carbon network. The observed endohedral nature is consistent with the presence a strong electron transfer interaction between encaged atom(s) and fullerene cages.