Isolation and Crystallographic Identification of Four Isomers of Sm@C90

Four isomers with the composition SmC90 were obtained from carbon soot produced by electric arc vaporization of carbon rods doped with Sm2O3. These were labeled Sm@C90(I), Sm@C90(II), Sm@C90(III), and Sm@C90(IV) in order of their elution times during chromatography on a Buckyprep column with toluene as the eluent. Analysis of the structures by single-crystal X-ray diffraction on cocrystals formed with Ni(octaethylporphyrin) reveals the identities of the individual isomers as follows: I, Sm@C2(40)-C90; II, Sm@C2(42)-C90; III, Sm@C2v(46)-C90 and IV, Sm@C2(45)-C90. This is the most extensive series of isomers of any endohedral fullerene to have their individual structures determined by single-crystal X-ray diffraction. The cage structures of these four isomers can be related pairwise to one another in a formal sense through sequential Stone−Wales transformations.通过对掺杂三氧化二钐（Sm₂O₃）的碳棒进行电弧汽化法制备碳灰，从中分离出四种组成为SmC₉₀的异构体。以甲苯为洗脱剂，在Buckyprep柱上开展色谱分离时，依照洗脱先后顺序将这四种异构体分别标记为Sm@C₉₀(I)、Sm@C₉₀(II)、Sm@C₉₀(III)与Sm@C₉₀(IV)。通过对与八乙基卟啉合镍（Ni(octaethylporphyrin)）形成的共晶进行单晶X射线衍射结构分析，可明确各异构体的具体结构如下：I为Sm@C₂(40)-C₉₀，II为Sm@C₂(42)-C₉₀，III为Sm@C₂v(46)-C₉₀，IV为Sm@C₂(45)-C₉₀。这是迄今已通过单晶X射线衍射解析单个异构体结构的内嵌富勒烯（endohedral fullerene）系列中，涵盖异构体数量最多的一组。从形式逻辑上而言，这四种异构体的笼状结构可通过连续的斯通-威尔士（Stone−Wales）变换实现两两关联。