Dimetallofullerene M2@C100 or carbide cluster fullerene M2C2@C98 (M = La, Y, and Sc): which ones are more stable?

The geometric and thermodynamic stability of the M2C100 (M -La, Y, and Sc) series was systematically investigated using density functional theory calculations on the level of B3LYP/6-31G(d) similar to Lanl2dz. In all the cases, M-2@D-5(285913)-C-100 isomers are the lowest-energy species. However, carbide endohedral fullerenes M2C2@ C-1(230933)-C-98 present excellent thermodynamic stabilities, except for those with La metal. The main product in electric arc experiments at temperatures lower than 3500 K for La2C100 should be La-2@ D-5(285913)-C-100, which was successfully synthesized previously; for Y and Sc, the predicted main products in these experiments should be M2C2@ C-1(230933)-C-98. Further analysis of the geometric structures of the M2C100 series showed that the dimetallofullerenes M-2@C-100 have greater effects on the shapes of cages than M2C2@C-98. These results provide some valuable guidance for the synthesis and characterization of large endohedral fullerenes including La, Y or Sc.