Stabilizing a three-center single-electron metal–metal bond in a fullerene cage

Abstract

Trimetallic carbide clusterfullerenes (TCCFs) encapsulating a quinary M₃C₂ cluster represent a special family of endohedral fullerenes with an open-shell electronic configuration. Herein, a novel TCCF based on a medium-sized rare earth metal, dysprosium (Dy), is synthesized for the first time. The molecular structure of Dy₃C₂@I_h(7)-C₈₀ determined by single crystal X-ray diffraction shows that the encapsulated Dy₃C₂ cluster adopts a bat ray configuration, in which the acetylide unit C₂ is elevated above the Dy₃ plane by ∼1.66 Å, while Dy–Dy distances are ∼3.4 Å. DFT computational analysis of the electronic structure reveals that the endohedral cluster has an unusual formal charge distribution of (Dy₃)⁸⁺(C₂)²⁻@C₈₀⁶⁻ and features an unprecedented three-center single-electron Dy–Dy–Dy bond, which has never been reported for lanthanide compounds. Moreover, this electronic structure is different from that of the analogous Sc₃C₂@I_h(7)-C₈₀ with a (Sc₃)⁹⁺(C₂)³⁻@C₈₀⁶⁻ charge distribution and no metal–metal bonding.