Bonding features in endohedral metallofullerenes. Topological analysis of the electron density distribution

A topological analysis of electron density and its Laplacian is carried out for the endohedral metallofullerenes Sc2@C84 and Ca@C72 to disclose the general features of chemical bonding. In both Sc2@C84 and Ca@C72, the metal–carbon bonds are highly ionic with strong anisotropy, due to electron transfer from the metal to the carbon cage. The C–C bonds are strongly covalent with π character even after receiving electrons from the metals. In Sc2@C84, the interaction between the two Sc atoms has weak covalent character.