Fullerene

A fullerene is an allotrope of carbon whose molecules consist of carbon atoms connected to form a closed cage. The molecules may have hollow sphere- and ellipsoid-like forms, tubes, or other shapes. The carbons are usually arranged in 5- and 6-membered rings. The family is named after buckminsterfullerene (C₆₀), which in turn is named after Buckminster Fuller. C₆₀ is also the first discovered and best characterized fullerene. C₆₀ has a hollow sphere-like form, but other fullerenes are known with ellipsoid-like shapes.

The closed fullerenes, especially C₆₀, are also informally called buckyballs for their resemblance to the standard ball of association football. IUPAC defines fullerenes as "polyhedral closed cages made up entirely of n three-coordinate carbon atoms and having 12 pentagonal and (n/2-10) hexagonal faces, where n ≥ 20."