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

Abstract

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 I_h symmetric C₈₀ isomer as La does in La₂@C₈₀. We have found that Ce₂@C₈₀ has a D_3d 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 D_2h symmetric. The two Ce atoms inside the C₈₀-I_h 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 D_3d configuration.