Structure of Endohedral Dimetallofullerene Sc2@C84

The endohedral nature of dimetallofullerene S${\mathrm{c}}_2$@${\mathrm{C}}_{84}$ is determined for the first time by a method which is a combination of the maximum entropy method (MEM) and the Rietveld refinement from synchrotron powder diffraction data. The obtained MEM charge density clearly shows the $D_{2d}$-symmetry cage structure, indicating the rotation of S${\mathrm{c}}_2$@${\mathrm{C}}_{84}$ molecules in solid state is almost quenched even at room temperature. From the MEM charge density, the encapsulated Sc-Sc distance and the nearest Sc-C distance are 3.9(1) and 2.4(1) Å, respectively.