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

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-@C₈₀ ^6- 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-@C₈₀ ^6- charge distribution and no metal-metal bonding.