Density functional calculations have been performed on Sc3N@C-80 and Sc3N@C-78 to examine the bonding between the scandium atoms and the fullerene cage. The encapsulation of the Sc3N unit is a strongly exothermic process that is accompanied by a formal transfer of six electrons from the scandium atoms to the fullerene cage in both complexes. In the case Of Sc3N@C-78, the metal ions are strongly linked to three [6:6] ring junctions of three different pyracylene patches, which are located at the midsection of the fullerene cage. This bonding restricts the Sc3N unit from freely rotating inside the cage. Geometric optimization of the structure Of Sc3N@C-78 indicates that the carbon cage expands to accommodate the Sc3N unit within the cage. This optimized structure has been used to re-refine the crystallographic data for {Sc3N@C-78} (.) {Co(OEP)} (.) 1.5-(C6H6) (.) 0.3(CHCl3). In contrast, in Sc3N@C-80, the Sc3N unit is not trapped in a specific position within the inner surface of the I-h cage, which is an unusual fullerene that lacks pyracylene patches. Thus, free rotation of the Sc3N group within the C-80 cage is expected. Despite the electronic transfer from the Sc3N unit to the carbon cage, Sc3N@C-78 and SC3N@C-80 have relatively large electron affinities and ionization potentials.