Theoretical Study of Structures and Chemical Functionalization of Endohedral Metallofullerenes

溝呂木, 直美; ミゾロギ, ナオミ; MIZOROGI, Naomi

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Theoretical Study of Structures and Chemical Functionalization of Endohedral Metallofullerenes

https://ir.soken.ac.jp/records/247

名前 / ファイル	ライセンス	アクション
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Item type

学位論文 / Thesis or Dissertation(1)

公開日

2010-02-22

タイトル

Theoretical Study of Structures and Chemical Functionalization of Endohedral Metallofullerenes

タイトル

Theoretical Study of Structures and Chemical Functionalization of Endohedral Metallofullerenes

言語

eng

資源タイプ

資源タイプ識別子

http://purl.org/coar/resource_type/c_46ec

資源タイプ

thesis

著者名

溝呂木, 直美

フリガナ

ミゾロギ, ナオミ

著者

MIZOROGI, Naomi

学位授与機関

学位授与機関名

総合研究大学院大学

学位名

博士（理学）

学位記番号

内容記述タイプ

Other

内容記述

総研大甲第1025号

研究科

値

物理科学研究科

専攻

値

07 構造分子科学専攻

学位授与年月日

2007-03-23

学位授与年度

値

2006

要旨

内容記述タイプ

Other

内容記述

Endohedral metallofullerenes (fullerenes encapsulating metal atoms inside the hollow spherical cages)have long attracted wide interest because of the promising material, catalytic, and biomedical applications. The electronic properties and reactivities of endohedral metallofullerenes have been extensively investigated both theoretically and experimentally. It is currently the focus of interest to determine the cage structures and metalpositions, since these are fundamental in the investigation and application of endohedral metallofullerenes. 　In this thesis, she has disclosed (1) the cage structures of the representative trimetallofullerene Sc3 C82 and dimetallofullerene Sc2C84, (2) the metal positions for Ce@C82, Eu@C82, Eu@C82 and Gd@C82, (3) how the encapsulation of La2 and Sc3N indside C80 tunes the reactivities of the C80 cage, and (4) how the rotationalmotion of La2 and Sc3N inside C80 in controllable by exohedral chemical functionalization, by using densityfunctional calculations in collaboration with experiment. 　(1) It is widely accepted that the maximum entropy method (MEM)/Rietveld analysis of synchrotron X-ray powder diffraction data is powerful for structural determination of endohedral metallofullerenes. Since the first application to Y@C82, the structured of many representative metallofullerenes have been determined and reported by the MEM/Rietveld method. For example, the MEM/Rietveld analysis of Sc3C82 shows that three Sc atoms are encapsulated inside a C3v isomer of C82 as a trimer. However, this Sc3@C82 structure does not correspond to an energy minimum. From density functional calculrations and 13C NMR data, it has been disclosed that the cage structure of Sc3C82 originates from the Ih isomer of C80 (not from the C3v isomer of C82)and two C atoms as well as three Sc atoms are encaged inside the C80 fullerene, the Sc3C2@C80 structure being much more stable than the Sc3@C82 structure determined by the MEM/Rietveld analysis. This noticeable finding has been corroborated by the single-crystal X-ray diffraction analysis of a carbine derivative of Sc3C2@C80. The carbide metallofullerene, Sc3C2@C80, is noteworthy since the number of encapsulated atomsis the largest known up to now. As another interesting example, it has been disclosed that Sc2C84 takes the from of Sc2C2@C82, though Sc2C84 has been believed to have the form of Sc2@C84 from the MEM/Rietveld analysis. These results suggest that the structures of endohedral metallofullerenes determined by the MEM/Rietveld analysis are not always reliable enough, though the determined structures have been widely employed to explain the electronic properties and reactivities as well as spectroscopic data. 　(2)Since the first successful extraction of La@C82(M=Sc, Y, and La ) has been known as atypical monometallofullerene. The M atom is mostly encapsulated inside the C2v cage of C 82 and located at an off-centered position near a hexagonal ring along the C2 axis. From the MEM/Rietveld analysis, however, it has been very recently claimed that Eu@C82 and Gd@C82 have exceptionally an anomalous endohedral structure since the metal atom having f electrons is located near the C-C double bond on the opposite side of the C2v-C82 cage along the C2 axis. To provide theoretical insight to this exception, density functional calculations were performed for Eu@C82 and Gd@C82 as well as Ce@C82. For all these metallofullerenes, it was found that the metal positions near the C-C double bond on the opposite side are highly unstable and do not correspond to energy minima, as also supported from the analysis of electrostatic potentials. The Eu, Gd, and Ce atoms move without any barrier to the positions near the hexagonal ring. The metal positions near the hexagonal ring are 30,52, and 50 kcal/mol more stable for Eu@C82, Gd@C82, and Ce@C82, respectively, than those near the C-Cdouble bond. These results suggest that Eu@C82, Gd@C82, and Ce@C82 have a normal endohedral structure, as found for M@C82(M=Sc, Y, and La). In collaboration with experiment, the normal structure of Ce@C82has been verified from the paramagnetic NMR spectral analysis of the anion. 　(3)Both La2@C80 and Sc3N@C80 have the same carbon cage that originates from the Ih isomer of C80 andthe electronic structures are formally described as (La2)6＋C806- and (Sc3N)6+C806- as a result of six-electron transfer to the C80 cage. However, Sc3.However, Sc3N@C80 has a much higher LUMO level than La2@C80. The LUMO of Sc3N@C80 is delocalized not only on the Sc3N cation but also on the C80 anion, while the LUMO of La2@C80 islocalized on the La cation and more suitable as an electron accommodation. These suggest that La2@C80 is more reactive toward nucleophiles than Sc3N@C80. In fact, the different reactivities of La2@C80 and Sc3N@C80 have been verified for the reactions with disilirane. As this example shows, it is interesting that the reactivities of metallofullerenes are tunable by encapsulated species. 　(4) For La2@C80 and Sc3N@C80, it is known that the two La atoms and the Sc3N cluster rotate freely inside the round Ih-C80 cage at room temperature. By density functional calculations, however, it was found that the two La atoms stand still at a specific position upon the exohedral chemical functionalization of La2@C80 by azomethine ylides, while the three-dimensional random motion of the Sc3N cluster in Sc3N@C80 is fixied in the plane perpendicular to the equator by attaching electron-donating molecules such as disilirane. These theoretical findings have been recently confirmed by experiment. Control of motion of encapsulated species within a hollow cage is expected to be helpful in designing molecular devices with electronic or magnetic properties.

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Theoretical Study of Structures and Chemical Functionalization of Endohedral Metallofullerenes

× 溝呂木, 直美

× ミゾロギ, ナオミ

× MIZOROGI, Naomi

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