Arc-discharge synthesis of Sc-based endohedral metallofullerenes in the presence of methane afforded formation of two new metallofullerene species, Sc 4 C 81 and Sc 4 C 83 , but their chromatographic separation proved to be difficult because of insufficient stability. Computational DFT studies are performed to reveal the possible molecular structures of these species. The first structural conjectures were based on the consideration of the Sc–carbon clusters comprising four Sc atoms and one or three carbon atoms in an icosahedral C 80 - I h (7) cage. For Sc 4 C@C 80 , the tetrahedral Sc 4 cluster with the central μ 4 -C atom was found to be 10 kJ/mol stable than the square cluster. For Sc 4 C 3 @C 80 , our calculation showed that the most stable is the Sc 4 C 3 cluster, in which the triangular C 3 moiety is η 3 - and η 2 -coordinated by Sc atoms. Whereas Sc 4 C@C 80 has rather small HOMO–LUMO gap and low ionization potential, the HOMO–LUMO gap of Sc 4 C 3 @C 80 is substantially higher and exceeds that of Sc 4 C 2 @C 80 . Thus, Sc 4 C 3 @C 80 is predicted to be a kinetically stable endohedral fullerene. At the same time, its thermodynamic stability is rather low and Sc 4 C@C 82 – C 2 v (9) is predicted to be 101 kJ/mol lower in energy than Sc 4 C 3 @C 80 - I h (7).