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 A 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.

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