Isolation and Crystallographic Characterization of La2C2@Cs(574)-C102 and La2C2@C2(816)-C104: Evidence for the Top-Down Formation Mechanism of Fullerenes

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• 作者：Wenting Cai ; Fang-Fang Li ; Lipiao Bao ; Yunpeng Xie ; Xing Lu
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：May 25, 2016
• 年：2016
• 卷：138
• 期：20
• 页码：6670-6675
• 全文大小：377K
• 年卷期：0
• ISSN：1520-5126

文摘

Tubular higher fullerenes are prototypes of finite-length end-capped carbon nanotubes (CNTs) whose structures can be accurately characterized by single-crystal X-ray diffraction crystallography. We present here the isolation and crystallographic characterization of two unprecedented higher fullerenes stabilized by the encapsulation of a La₂C₂ cluster, namely, La₂C₂@C_s(574)-C₁₀₂, which has a perfect tubular cage corresponding to a short (10, 0) zigzag carbon nanotube, and La₂C₂@C₂(816)-C₁₀₄ which has a defective cage with a pyracylene motif inserting into the cage waist. Both cages provide sufficient spaces for the large La₂C₂ cluster to adopt a stretched and nearly planar configuration, departing from the common butterfly-like configuration which has been frequently observed in midsized carbide metallofullerenes (e.g., Sc₂C₂@C_80–84), to achieve strong metal–cage interactions. More meaningfully, our crystallographic results demonstrate that the defective cage of C₂(816)-C₁₀₄ is a starting point to form the other three tubular cages known so far, i.e., D₅(450)-C₁₀₀, C_s(574)-C₁₀₂, and D_3d(822)-C₁₀₄, presenting evidence for the top-down formation mechanism of fullerenes. The fact that only the large La₂C₂ cluster has been found in giant fullerene cages (C_>100) and the small clusters M₂C₂ (M = Sc, Y, Er, etc.) are present in midsized fullerenes (C₈₀–C₈₆) indicates that geometrical matching between the cluster and the cage, which ensures strong metal–cage interactions, is an important factor controlling the stability of the resultant metallofullerenes, in addition to charge transfer.