An anomalous endohedral structure of Eu@c82 metallofullerenes.
An anomalous endohedral structure of Eu@c82 metallofullerenes.
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DOI：
10.1002/anie.200500876
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发表时间：
2005-07
影响因子：
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通讯作者：
Bao-Yun Sun;T. Sugai;E. Nishibori;Ken-ichi Iwata;M. Sakata;M. Takata;H. Shinohara
中科院分区：
文献类型：
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作者：
Bao-Yun Sun;T. Sugai;E. Nishibori;Ken-ichi Iwata;M. Sakata;M. Takata;H. Shinohara
三价金属富勒烯，如 La@ C82 和 Ce@ C82，其中金属离子更倾向于采用三价电荷态，已被广泛研究。 [1]然而，尽管在过去几年中开发了一些改进的生产和提取方法，但由于已知这些金属富勒烯的生产收率较低，因此对封装二价 Sm、Eu、Tm 和 Yb 金属离子的金属富勒烯的研究受到限制。 [2]这种情况导致此类金属富勒烯的结构尚未得到详细研究。被捕获的金属离子和电荷转移的多样性以及被捕获的金属离子的运动预计会提供不同的物理性质。因此，有必要研究该二价基团金属富勒烯的结构和电子性质。实验表明Eu@C82中的Eu离子可以将两个电子转移到富勒烯笼中。[2c]Eu@C82笼上没有不成对的电子，电荷转移导致电子构型为4f75d06s0，从而使富勒烯具有顺磁性。因此很难通过核磁共振波谱确定笼的结构和配合物的对称性。 XRD测量已成为了解Eu@C82富勒烯详细结构的唯一方法。结合最大熵法 (MEM) 和 Rietveld 精修（MEM/Rietveld 方法 [3]）进行的 X 射线分析已被证明是准确测定金属富勒烯结构的强大方法。该方法成功测定了La、Y、Sc、Gd@C82等一系列金属富勒烯的内嵌性质，[4]Sc3@C82、La2@C80、Sc2@C84、Sc2@C66和Sc2C2@C84[5]。本研究成功测定了Eu@C82(I、III)的两种异构体的结构。使用同步加速器 X 射线粉末衍射数据的 MEM/Rietveld 方法。 Eu@ C82 (III) 的内嵌结构是特殊的，因为 Eu 离子与 C2v 碳笼 C2 轴上的 C¿C 双键相邻，而普通单金属富勒烯中的金属离子（如 La、Y、Sc、Er、Lu）与 C82 笼的六边形相邻（Gd@ C82 除外）。[4d, 6]
Trivalent metallofullerenes such as La@ C82 and Ce@ C82, in which the metal ions prefer to take a trivalent charge state, have been extensively investigated.[1] However, studies on metallofullerenes encapsulating divalent Sm, Eu, Tm, and Yb metal ions have been limited because of the known low yields in the production of these metallofullerenes despite the development of some improved production and extraction methods during the past several years.[2] This situation has resulted in the structures of such metallofullerenes not having been studied in detail. The variety of encaged metal ions and charge transfer as well as the movement of entrapped metal ions are expected to provide different physical properties. Therefore, it is necessary to study the structure and electronic properties of metallofullerenes in this divalent group. The Eu ion in Eu@ C82 was shown by experiment to transfer two electrons to the fullerene cage.[2c] There are no unpaired electrons on the Eu@ C82 cage and charge transfer results in the 4f75d06s0 electronic configuration, which gives rise to the fullerene having paramagnetic character. It is thus difficult to determine the structure of the cage and the symmetry of the complex by NMR spectroscopy. XRD measurements have become the only way to access the detailed structure of Eu@ C82 fullerenes. X-ray analysis performed using a combination of the maximum entropy method (MEM) and Rietveld refinement (the MEM/Rietveld method [3]) has proven to be a powerful method for the accurate determination of the structures of metallofullerenes. The endohedral nature of a series of metallofullerenes, such as La, Y, Sc, and Gd@ C82,[4] Sc3@ C82, La2@ C80, Sc2@ C84, Sc2@ C66, and Sc2C2@ C84 [5] has been determined successfully by this method.In the present study the structures of the two isomers of Eu@ C82 (I, III) were successfully determined by the MEM/Rietveld method using synchrotron X-ray powder diffraction data. The endohedral structure of Eu@ C82 (III) is exceptional in view of the fact that the Eu ion is adjacent to the C¿ C double bond on the C2 axis of the C2v carbon cage, whereas the metal ions (such as La, Y, Sc, Er, Lu) in the normal monometallofullerenes are adjacent to a hexagon of the C82 cage, except for Gd@ C82.[4d, 6]