How to Stabilize a Heptagon-Containing C Cage by Endohedral Derivation.

Nonclassical fullerene is a new member of the fullerene family. In the present work, a systematic investigation on LaScN@C ( = 0-3) covering both classical and nonclassical C cages was performed utilizing density functional theory combined with statistical mechanics. At absolute zero, LaScN@-(2)-C with a heptagon-containing nonclassical carbon is the second most stable isomer, whereas at the temperature range of endohedral metallofullerene (EMF) formation, due to the large vibrational frequencies, LaScN@-(2)-C is the third most abundant isomer, and its mole fraction is very low, accounting for the low experimental yield of LaScN@-(2)-C; LaScN@-(2)-C, and LaN@-(2)-C are the overwhelming isomers of the corresponding series, but compared with the cases of ScN@C and LaScN@C, LaScN and LaN clusters suffer much larger constraints from the C cages, perhaps preventing the synthesis of LaScN@C and LaN@C species. Because of the large mole fractions and large electron donation and back-donation of LaScN@-(2)-C and LaN@-(2)-C, it can be inferred that LaScN and LaN clusters may be used to stabilize some other larger nonclassical fullerene cages. This work will provide useful insights into the origins of stabilization of nonclassical fullerene cages by endohedral derivation and guidelines for synthesis EMF with nonclassical cages.