Bonding in Endohedral Metal–Fullerene Complexes: f‐Orbital Covalency in Ce@C₂₈

Three conditions must be met if an endohedral metal–fullerene complex is to be stable : 1. Metal valence orbitals and fullerene frontier orbitals must have complementary symmetry. 2. The metal atomic orbitals must fit inside the fullerene cavity. 3. The resulting complex must have a closed‐shell configuration. According to scalar‐relativistic calculations these conditions are met in Ce@C₂₈. The binding energy is calculated to be 13.7 eV, and the Ce f orbitals contribute significantly to the covalent bond.