Theoretical Insight into Sc2C76: Carbide Clusterfullerene Sc2C2@C74 versus Dimetallofullerene Sc2@C76

In terms of density functional theory in combination with a statistical thermodynamic method, we have investigated the Sc2C76 species including dimetallofullerenes Sc2@C76 and carbide clusterfullerenes Sc2C2@C74. Two dimetallofullerenes, Sc2@Cs(17490)-C76 and Sc2@Td(19151)-C76, possess the lowest relative energies but exhibit poor thermodynamic stability within the fullerene-formation region (500–3000 K). In contrast, four carbide clusterfullerene isomers, Sc2C2@D3h(14246)-C74, Sc2C2@C2v(14239)-C74, Sc2C2@C2(13333)-C74, and Sc2C2@C1(13334)-C74, have excellent thermodynamic stability when considering the temperature effect. The Sc2C2@D3h(14246)-C74 isomer, which satisfies the isolated-pentagon rule (IPR), was characterized by its crystallographic structure; however, the other three non-IPR structures with two pairs of pentagon adjacencies are predicted for the first time. In particular, Sc2C2@C2(13333)-C74 and Sc2C2@C1(13334)-C74 are linked by a single Stone–Wales transformation. Meanwhile, bonding critica...