In chemistry, a metallofullerene is a molecule composed of a metal atom trapped inside a fullerene cage.
Simple metallofullerenes consist of a fullerene cage, typically , with one or two metal atoms trapped inside. Recently, research has produced metallofullerenes that enclose small clusters of atoms, such as , , and . The @ symbol in the formula indicates that the atom(s) are encapsulated inside the cage, rather than being chemically bonded to it.
Fullerenes in a variety of sizes have been found to encapsulate metal atoms in this way.