Dual Stabilization of a Tri-Metallofullerene Radical Er 3 @C 80 : Exohedral Derivatization and Endohedral Three-Center Bonding.

The enclosed space within fullerene molecules, capable of trapping metal clusters, offers an opportunity to investigate the behavior of metal atoms in a highly confined sub-nanometer environment. However, the studies on trimetallofullerenes M 3 @C 80 have been very limited due to their difficult obtainability. In this paper, we present a new method for obtaining a tri-metallofullerene Er 3 @C 80 through exohedral modification of the fullerene cage. Our findings reveal that Er 3 @C 80 exhibits a radical character and can react with the dichlorobenzene radical to generate a stable derivative Er 3 @C 80 PhCl 2 . Theoretical calculations demonstrate the presence of a three-center two-electron metal-metal bond in the center of the fullerene cage. This bond serves to counterbalance the Coulomb repulsion between the Er ions. Consequently, both exohedral derivatization and endohedral three-center bonding contribute to the substantial stability of Er 3 @C 80 PhCl 2 . Furthermore, molecular dynamics simulations indicate that the Er 3 cluster within the molecule possesses a rigid triangle structure. The availability of M 3 @C 80 derivatives opens avenues for future investigations into interactions among metal atoms, such as magnetic coupling, within fullerene cages.