Endohedral complexes: Atoms and ions inside the C₆₀ cage

The results of ab initio electronic structure calculations on the C₆₀ cage and its endohedral (‘‘inside‐the‐cage’’) complexes with F⁻, Ne, Na⁺, Mg²⁺, and Al³⁺ are presented. Placing the ions at the center of the cage results in a net stabilization and screening of the charges. The ionic guests either decrease (F⁻) or increase (Na⁺, Mg²⁺, and Al³⁺ ) the cage radii. The complexes with the ions at the cage center are local maxima with respect to the displacement of the guests. The C₆₀⋅Ne complex, which is destabilized by ca. 0.4 kcal/mol relative to the separated components, is an energy minimum. In the C₆₀⋅Na⁺ complex, the energy minimum (which lies only 0.8 kcal/mol below the maximum) corresponds to the Na atom displaced by 0.66 Å from the cage center. The calculated properties of the endohedral complexes are easily rationalized with a model involving a double‐layer polarizable C₆₀ cage affected by the electrostatic potential produced by the enclosed guests.