Adsorption of Clusters on Clean Surfaces

面内金属富勒烯是一种基于富勒烯的新型材料，在过去的四年里引起了人们的极大关注。近几年来，用同步辐射X射线衍射法和~(13)C-核磁共振法对金属富勒烯进行“直接”结构分析取得了一些重要进展。最近，我们成功地测定了金属富勒烯Y@C82的面内性质，并通过同步加速器X射线粉末衍射获得了它的总电子密度(1)。结果表明，Y原子偏离了C82分子的中心，并强烈结合在碳笼上。在本研究中，首次用高分辨~(13)C-核磁共振谱和同步辐射X-射线衍射法确定了典型的双金属富勒烯SC2@C84的异构体和面内结构。结果表明，SC2@C84的主要异构体之一，即SC2@C84(III)具有D2D(23)对称性，Sc离子在最佳Sc位置附近可能发生了一些动力学平均。这与Y@C82的情况形成了鲜明的对比，在Y@C82的情况下，即使在室温下，Y原子也附着在碳笼上。文中还给出并讨论了Y@C82和SC2@C84的一些重要的晶体结构特征。

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 analyzes 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 di- metallofullerene, 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 were also presented and discussed.