M @ C60 endohedral complexes, which are based on the C60 molecule and
contain encapsulated atoms M, would provide a unique opportunity to ta
ilor specific properties of the C60 system on a molecular level. The s
tability of these complexes is calculated using a Born-Haber cycle tha
t was originally applied to determine the formation enthalpy of solid
C60 intercalation compounds. We find that the formation energy of M @
C60 depends crucially on the ionization potential and electron affinit
y of the endohedral atom and the C60 molecule. A significant contribut
ion to the formation energy comes from the polarization energy of the
cage if the enclosed atom is not at the cage center; this finding is i
n agreement with available ab initio results. We discuss the potential
of these systems to become a new class of superconducting materials.