Explanation of the different preferential binding sites for Ce and La in M2@C80 (M = Ce, La)—a density functional theory prediction

Metallofullerenes have many possible uses in technology and even in bio-medical applications. Some fullerenes have been found to have two incarcerated metal atoms such as M2@C80 (M = La, Ce, etc.). We have calculated the structural and electronic properties of Ce2@C80 using density functional theory (DFT). Ce is known to be preferentially incorporated into the Ih symmetric C80 isomer as La does in La2@C80. We have found that Ce2@C80 has a D3d symmetric ground state structure and that Ce binds to a different type of binding site compared to other cerium containing fullerenes, such as Ce@C82. This binding site also differs compared to La in La2@C80, which is D2h symmetric. The two Ce atoms inside the C80-Ih cage are equivalent and retain their f-electron. The Ce atoms bind on-top of one carbon atom (and its three neighbors) in Ce2@C80, compared to in the center of a six-membered ring as in C82. This novel binding site minimizes Ce(f)⋯Ce(f) overlap in favour of Ce–C bonding, giving the D3d configuration.