Isolation and Crystallographic Characterization of Sm@<i>C</i>_2v(3)‑C₈₀ Through Cocrystal Formation with Ni^II(octaethylporphyrin) or Bis(ethylenedithio)tetrathiafulvalene

Sm@C2v(3)-C80 has been separated from the carbon soot produced by electrical arc vaporization of graphite rods doped with Sm2O3 and purified. Its structure has been determined by single crystal X-ray diffraction using cocrystals obtained from either NiII(octaethylporphyrin) (NiII(OEP)) to form Sm@C2v(3)-C80·NiII(OEP)·1.68­(toluene)·0.32­(benzene) or bis­(ethylenedithio)-tetrathiafulvalene (ET) to produce Sm@C2v(3)-C80·ET·0.5­(toluene). Thus, this study offers the first opportunity to compare a common endohedral fullerene in two different cocrystals. Both cocrystals provide consistent information on the basic structure of Sm@C2v(3)-C80 but show that the distribution of samarium ion sites inside the carbon cage depends upon whether NiII(OEP) or ET is present. The samarium ion is disordered in both structures, but the prominent sites lie slightly off the 2-fold symmetry axis of the cage. Computational studies at the B3LYP level indicate that Sm@C2v(3)-C80 is more stable than any of the other six isomers of Sm@C80 that obey the isolated pentagon rule (IPR). The surface electrostatic potential of the interacting components in the cocrystals has been examined to identify factors responsible for the ordering of the fullerene cages. The regions of the NiII(OEP) or ET molecules that are closest to the fullerene display negative potential, while the corresponding regions of the endohedral fullerene show positive potential in a consistent fashion in both cocrystals.Sm@C2v(3)-C80已从掺杂氧化钐（Sm₂O₃）的石墨棒经电弧汽化产生的炭黑中分离并纯化。其结构通过单晶X射线衍射(single crystal X-ray diffraction)测定，所用共晶分别通过两种途径制备：一是与二价镍八乙基卟啉（NiII(octaethylporphyrin), NiII(OEP)）形成加合物Sm@C2v(3)-C80·NiII(OEP)·1.68­甲苯·0.32­苯；二是与双(乙二硫基)四硫富瓦烯(bis(ethylenedithio)-tetrathiafulvalene, ET)得到加合物Sm@C2v(3)-C80·ET·0.5­甲苯。本研究首次实现了同一普通内嵌富勒烯(endohedral fullerene)在两种不同共晶体系中的对比研究。两种共晶均给出了Sm@C2v(3)-C80基本结构的一致信息，但证实碳笼内部钐离子的位点分布会因共晶客体为NiII(OEP)还是ET而有所差异。两种结构中的钐离子均存在无序现象，但其优势位点略微偏离碳笼的二重对称轴。在B3LYP水平下开展的计算研究表明，Sm@C2v(3)-C80的稳定性优于其余6种符合孤立五边形规则(isolated pentagon rule, IPR)的Sm@C80异构体。本研究还考察了共晶中相互作用组分的表面静电势(surface electrostatic potential)，以明确影响富勒烯笼排布的关键因素。结果显示，与富勒烯最邻近的NiII(OEP)或ET分子区域呈现负静电势，而内嵌富勒烯的对应区域在两种共晶中均一致表现出正静电势。