The energy variation during the formation of the titled endohedral complexes X@C-60 (X=atoms of the Group IA or the Group VIIA), and the bonding nature and the variation character or the at in C-60 cage all have been investigated from the viewpoint of intramolecular interaction. The results demonstrated that (1) the force field in C-60 cage is of nearly spherical symmetry; (2) the total interaction and its components vary regularly with the atomic numbers or radii, of X; (3) all concerned endohedral atoms except for I, contribute considerably to the stabilities of X@C-60 by way of the interaction between C-60 cage and them; (4) each X has a special energy minimum location in the cage, at or off the cage center, and this location is due to the resultant effect from the various interactions, but not to the formation of chemical bond between X and C-60 cage; (5) in settee, the interaction in C-60 cage is of typical non-bonding characteristics, with similar to 90% electrostatic interaction and similar to 10% repulsive and dispersive interactions.
