A computational study on Sc2S@C68 and Sc2O2@C68

Abstract

In order to predict the structures of the detected and assumed endohedral metallofullerene Sc₂S@C₆₈, and Sc₂O₂@C₆₈, and provide insights into their structures and properties, we have studied all of the isomers of C₆₈ and tens of candidate isomers of Sc₂S@C₆₈ and Sc₂O₂@C₆₈. The results show that Sc₂S@C₆₈ shares the same parent cage as Sc₂C₂@C₆₈:6073, however Sc₂O₂ is ready to be encaged inside C₆₈:6094. The calculations demonstrate that the transferred electrons from the encaged Sc₂S and Sc₂O₂ clusters stabilize the active cages. Sc₂S is V-shaped inside the cage whereas Sc₂O₂ is square-like inside the cage. Interestingly, the two Sc atoms of Sc₂O₂@C₆₈ have no tendency to bond with the two fused pentagons of C₆₈:6094 and unusually form a Sc–Sc single bond. The calculations show that encagement of Sc₂O₂ in C₆₈:6094 is more favourable than that of Sc₂S inside C₆₈:6073, and that the HOMO–LUMO gap of Sc₂O₂@C₆₈ is evidently broader than that of Sc₂S@C₆₈. These results suggest that there is a distinct possibility that the detected compound is Sc₂O₂@C₆₈ and at least Sc₂O₂@C₆₈ is much easier to synthesize under similar experimental conditions. The MS and UV spectra are provided to help their structural identification in the future.