Synchrotron X-ray diffraction and 13C-NMR studies on the isolated Y@C82 and Sc2@CS4 metallofullerenes

Endohedral metallofullerenes are novel fullerene-based materials and have attracted much attention in the last four years. In the last couple of years, some important progress have been made in ''direct'' structural analyses of metallofullerenes by using synchrotron X-ray diffraction and 13C-NMR studies. Recently, we have succeeded in determining the endohedral nature of the metallofullerene, Y@C82, and obtaining its total electron density via synchrotron X-ray powder diffraction(1). The results reveal that the yttrium atom is displaced from the center of the C82 molecule and is strongly bound to the carbon cage. In the present study, both the isomer and the endohedral structures of a typical dimetallofullerene, Sc2@C84, have been determined for the first time by high-resolution 13C-NMR (2) and synchrotron X-ray diffraction studies, respectively. The results show that one of the major isomer of Sc2@C84, i.e., Sc2@C84 (III), has a D2d (23) symmetry and that some dynamical averaging of the Sc ions might be taking place around the optimum scandium position. This is a striking contrast to the Y@C82 case, where the yttrium atom is attached to the carbon cage even at room temperature. Some important features of the crystal structures of Y@C82 and Sc2@C84 are also presented and discussed.