Anomalous endohedral structure of Gd @ C 82 metallofullerenes

An anomalous endohedral structure of $\mathrm{Gd}@{\mathrm{C}}_{82}$ metallofullerenes has been revealed by synchrotron radiation powder structure analysis by using the maximum entropy method. The $\mathrm{Gd}@{\mathrm{C}}_{82}$ metallofullerene has ${\mathrm{C}}_{82}{\ensuremath{-}C}_{2\mathrm{V}}$ cage structure as for $\mathrm{Sc}@{\mathrm{C}}_{82}$ and $\mathrm{La}@{\mathrm{C}}_{82}$ fullerenes. The Gd atom is located in the vicinity of the C-C double bond on the ${C}_{2}$ molecular axis in the ${\mathrm{C}}_{82}{/C}_{2\mathrm{V}}$ cage, which is the opposite end of the six-membered ring where Sc and La atoms in $\mathrm{Sc}@{\mathrm{C}}_{82}$ and $\mathrm{La}@{\mathrm{C}}_{82}$ are known to be placed. Furthermore, a significant overlap of the electron density distribution has been found between Gd atoms and carbon cages. A significantly polarized distribution of electrons has also been found on the carbon cage around the encapsulated Gd atom.