Metallofullerenes

Metallofullerenes are a class of endohedral fullerenes in which a metal atom or a metal cluster is encapsulated inside a hollow carbon cage, typically C60, C70, or C82. They are distinguished from exohedral metal-doped fullerenes, where metal atoms reside outside the cage. Endohedral metallofullerenes include single-atom species M@C60 and M@C82 as well as clusterfullerenes such as M3N@C80, in which a metal nitride cluster resides inside the cage.

Electronic structure and properties are governed by charge transfer between the encapsulated metal and the carbon cage. The metal often donates electrons to the fullerene, leading to a filled or partially filled cage electronic shell and distinctive redox behavior. The resulting complexes can exhibit defined spin states and modified optical properties relative to empty cages. The presence of unpaired electrons in the metal center can impart paramagnetic character, making metallofullerenes of interest for studies in molecular magnetism, spintronics, and quantum information.

Synthesis and isolation are typically achieved by high-temperature methods such as arc-discharge or laser ablation of graphite in the presence of a suitable metal source. The reaction mixture contains a variety of fullerenes, including endohedral species, which are then separated by chromatography, especially high-performance liquid chromatography, to yield pure metallofullerenes. Purification can be challenging, and yields are generally low.

Notable examples include Sc3N@C80, Sc2@C80, La@C60, Y@C82, and Gd@C82. Applications discussed in the literature include fundamental studies of electron transfer and spin states, as well as exploration of metallofullerenes for molecular electronics and imaging, though practical use is limited by synthesis scale and stability considerations.