Determination of the cage structure of Sc@C82 by synchrotron powder diffraction

The cage structure of Sc@C82 (isomer I) has been determined by a synchrotron radiation powder structural analysis using the maximum entropy method (MEM). From the MEM charge density obtained the cage structure of the endohedral Sc@C82 (I) is experimentally determined to have C2V symmetry. Inside the carbon cage, the Sc atom is located at an off-center position adjacent to a carbon six-membered ring. The nearest Sc–C distance determined from the MEM charge density is 2.53(8) Å. The charge transfer from Sc to C has been estimated to be 2.2e, which is consistent with the ultraviolet photoelectron spectra and theoretical results.