Sc3N@C80:: Computations on the two-isomer equilibrium at high temperatures

Reported herein are computations on the relative concentrations of the two experimentally known isomers of Sc3N@C-80, that is, those produced by encapsulation of Sc3N in two particular C-80 cages that obey the isolated-pentagon rule, namely, with I-h and D-5h symmetries. The calculations are based on density functional methods and have been carried out using the Gibbs energy over a brood temperature interval. It has been computed that, if a relatively free motion of the encapsulate inside the cages is allowed, the observed populations of 10 and 17% for the D-5h Sc3N@C-80 species are reached at temperatures of 2700 and 2450 K, respectively. The inclusion of the entropy term is essential as, if it is neglected, the D-5h Sc3N@C-80 population at a temperature of 2100 K would be a mere 1%, owing to the relatively large interisomeric separation potential energy of 19 kcal mol(-1).