Materials science: C66 fullerene encaging a scandium dimer

The geometry of carbon cages (fullerenes) is governed by the isolated-pentagon rule (IPR), which states that the most stable fullerenes are those in which all pentagons are surrounded by five hexagons. Although this rule has been verified experimentally, it is impossible for fullerenes in the range C60 to C70 to obey it. Here we describe the production and characterization of an IPR-violating metallofullerene, Sc2 @C66 , a C66 fullerene encaging a scandium dimer. Our results indicate that encapsulation of the metal dimer significantly stabilizes this otherwise extremely unstable C66 fullerene.