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

Trimetallic carbide clusterfullerenes (TCCFs) encapsulating a quinary M(3)C(2) 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 Dy(3)C(2)@I(h)(7)-C(80) determined by single crystal X-ray diffraction shows that the encapsulated Dy(3)C(2) cluster adopts a bat ray configuration, in which the acetylide unit C(2) is elevated above the Dy(3) 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 (Dy(3))(8+)(C(2))(2−)@C(80)(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 Sc(3)C(2)@I(h)(7)-C(80) with a (Sc(3))(9+)(C(2))(3−)@C(80)(6−) charge distribution and no metal–metal bonding.