Carbide clusterfullerenes with odd number of carbon atoms: molecular and electronic structures of Sc4C@C80, Sc4C@C82, and Sc4C3@C80

Arc-discharge synthesis of Sc-based endohedral metallofullerenes in the presence of methane afforded formation of two new metallofullerene species, Sc4C81 and Sc4C83, 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 Sc4C@C-80, the tetrahedral Sc-4 cluster with the central mu(4)-C atom was found to be 10 kJ/mol stable than the square cluster. For Sc4C3@C-80, our calculation showed that the most stable is the Sc4C3 cluster, in which the triangular C-3 moiety is eta(3)- and eta(2)-coordinated by Sc atoms. Whereas Sc4C@C-80 has rather small HOMO-LUMO gap and low ionization potential, the HOMO-LUMO gap of Sc4C3@C-80 is substantially higher and exceeds that of Sc4C2@C-80. Thus, Sc4C3@C-80 is predicted to be a kinetically stable endohedral fullerene. At the same time, its thermodynamic stability is rather low and Sc4C@C-82-C-2v(9) is predicted to be 101 kJ/mol lower in energy than Sc4C3@C-80-I-h(7).