As a result of a dual stabilization mechanism involving exohedral derivatization and endohedral three-center bonding, a trimetallofullerene radical, Er₃@C₈₀, is captured for the first time.

Abstract

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 M₃@C₈₀ have been very limited due to their difficult obtainability. In this paper, we present a new method for obtaining a tri-metallofullerene Er₃@C₈₀ through exohedral modification of the fullerene cage. Our findings reveal that Er₃@C₈₀ exhibits a radical character and can react with the dichlorobenzene radical to generate a stable derivative Er₃@C₈₀PhCl₂. 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 Er₃@C₈₀PhCl₂. Furthermore, molecular dynamics simulations indicate that the Er₃ cluster within the molecule possesses a rigid triangle structure. The availability of M₃@C₈₀ derivatives opens avenues for future investigations into interactions among metal atoms, such as magnetic coupling, within fullerene cages.