Theoretical Insight into ScC: Carbide Clusterfullerene ScC@C versus Dimetallofullerene Sc@C.

In terms of density functional theory in combination with a statistical thermodynamic method, we have investigated the ScC species including dimetallofullerenes Sc@C and carbide clusterfullerenes ScC@C. Two dimetallofullerenes, Sc@C(17490)-C and Sc@T(19151)-C, possess the lowest relative energies but exhibit poor thermodynamic stability within the fullerene-formation region (500-3000 K). In contrast, four carbide clusterfullerene isomers, ScC@D(14246)-C, ScC@C(14239)-C, ScC@C(13333)-C, and ScC@C(13334)-C, have excellent thermodynamic stability when considering the temperature effect. The ScC@D(14246)-C 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, ScC@C(13333)-C and ScC@C(13334)-C are linked by a single Stone-Wales transformation. Meanwhile, bonding critical points and Mayer bond orders in the four isomers were analyzed to disclose the unique interactions between the inner clusters and cages. Additionally, the structural characteristics, C and Sc NMR chemical shifts, and IR spectra of the four stable isomers are introduced to assist experimental identification and characterization in the future.