heterofullerene

Heterofullerenes are fullerene-type carbon cages in which one or more carbon atoms in the cage are replaced by other elements (heteroatoms). The substitution yields molecules that retain the spherical or ellipsoidal geometry of C60 and related fullerenes but with altered electronic structure and chemistry. Common forms include azafullerenes, in which a carbon atom is replaced by nitrogen (for example C59N); boron-doped fullerenes, where boron substitutes carbon (such as C59B); and other substitutions with elements such as silicon or phosphorus in suitably defined cages. These species are distinct from endohedral fullerenes, which confine atoms inside the cage rather than replacing cage atoms.

Synthesis and isolation are typically achieved by high-energy methods such as arc-discharge or laser ablation of graphite in atmospheres containing nitrogen, boron, or other dopants. Substitution can also be achieved via post-synthesis chemical modification of fullerene precursors. The products are usually isolated by chromatographic techniques and characterized by mass spectrometry, UV–Vis–NIR spectroscopy, electron paramagnetic resonance for radical species, and X-ray crystallography when crystals are obtainable.

Properties and applications: Substitution modifies the cage's symmetry, bond lengths, and electronic distribution, often altering electron affinity and redox behavior. Some heterofullerenes exhibit unique reactivity or spin properties that attract interest for organic electronics, photovoltaics, and molecular materials research. Stability varies with the dopant and substitution level, and many heterofullerenes are sensitive to moisture or oxygen, requiring careful handling and storage.