Kinetic stability of carbon cages in non-classical metallofullerenes

Charged carbon cages in isolable metallofullerenes are kinetically stable with a minimum bond resonance energy (min BRE)>−0.100 |β|. Charged carbon cages with adjacent pentagons in recently isolated non-classical metallofullerenes, Sc2@C66 and Sc3N@C68, are not exceptions. In fact, many molecular anions of fullerenes with adjacent pentagons have a large negative min BRE. Nature seems to choose carbon cages from among a small number of kinetically stable fullerene molecular anions with adjacent pentagons to design isolable non-classical metallofullerenes. There is no doubt that the isolated pentagon rule cannot be applied to charged fullerenes.