Triangle Scandium Cluster Imprisoned in a Fullerene Cage

The endohedral structure of tri-metallofullerene ${\mathrm{Sc}}_3@{\mathrm{C}}_{82}$ is determined by the maximum entropy method (MEM) combined with the Rietveld method using synchrotron radiation powder data. The result reveals for the first time that Sc atoms are encapsulated in the form of a triangle Sc cluster inside the ${\mathrm{C}}_{3V}-{\mathrm{C}}_{82}$ fullerene. The charge state of the encaged trimer is also determined as ${\mathrm{Sc}}_3^{3+}@{\mathrm{C}}_{82}^{3-}$ from the MEM charge density. The Sc-Sc distance in the equilateral triangular ${\mathrm{Sc}}_3$ cluster is 2.3(3) Å