Proof for trivalent Sc ions in ${\mathrm{Sc}}_2@{\mathrm{C}}_{84}$ from high-energy spectroscopy

The electronic structure and the valency of the Sc ions in the endohedral dimetallofullerene ${\mathrm{Sc}}_2@{\mathrm{C}}_{84}$ with $D_{2d}$ symmetry are probed using high-energy spectroscopy. Comparison of the Sc $2\overrightarrow{p}3d$ x-ray-absorption spectrum with calculated ionic multiplet spectra shows that the Sc ions are trivalent. Detailed multiplet calculations including covalency indicate that the effective valency of the Sc(III) ions can be described by a formal charge transfer to the fullerene cage of $2.6\pm \mathrm{0.1.}$ This illustrates that a purely ionic picture is not valid for the electronic structure of ${\mathrm{Sc}}_2@{\mathrm{C}}_{84},$ and that a more complex picture including finite hybridization between the Sc and the fullerene cage has to be applied.