Theoretical Insights into Monometallofullerene Th@C₇₆: Strong Covalent Interaction between Thorium and the Carbon Cage

Th@C₇₆ has been studied by density functional theory combined with statistical mechanics calculations. The results reveal that Th@T_d(19151)-C₇₆ satisfying the isolated pentagon rule possesses the lowest energy. Nevertheless, considering the enthalpy–entropy interplay, Th@C₁(17418)-C₇₆ with one pair of adjacent pentagons is thermodynamically favorable at elevated temperatures, which is reported for the first time. The bonding critical points in both isomers were analyzed to disclose covalent interactions between the inner Th and cages. In addition, the Wiberg bond orders of M–C bonding in different endohedral metallofullerenes (EMFs) were investigated to prove stronger covalent interactions of Th–C in Th-based EMFs.