Sc2@C76(C2): a new isomerism in fullerene structure

Sc2@C76 was for the first time isolated and characterized spectroscopically. It is suggested from the 13C NMR spectroscopy (13C NMR pattern: 38×2) that this metallofullerene has a C2 symmetry, in contrast to the D2 symmetry of an empty C76 fullerene cage. Ab initio calculations were performed to explore the symmetry changes for C76 (from D2 to C2) induced by the endohedral scandium ions. It is found that the scandium ions are located at two of the three main C2 axes of C76(D2). The two isomers Sc2@C76(D2−x) (Sc2 was put along the C2x axis of C76(D2)) and Sc2@C76(D2−y) (Sc2 was put along the C2y axis of C76(D2)) are nearly iso-energetic in their optimised geometrical structures, and their energies are much lower than that of the third isomer Sc2@C76(D2−z) (Sc2 was put along the C2z axis of C76(D2)). Each of the two iso-energetic isomers, i.e., Sc2@C76(D2−x) and Sc2@C76(D2−y), contributes 19 NMR lines (13C NMR pattern: 19×4), so the mixture of them shows overall 38 NMR lines (13C NMR pattern: 38×2) for this metallofullerene.