U-2@I-h(7)-C-80: Crystallographic Characterization of a Long-Sought Dimetallic Actinide Endohedral Fullerene
U-2@I-h(7)-C-80: Crystallographic Characterization of a Long-Sought Dimetallic Actinide Endohedral Fullerene
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U-2@I-h(7)-C-80：长期寻找的双金属锕系内嵌富勒烯的晶体学表征
DOI：
10.1021/jacs.7b10865
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发表时间：
2018
影响因子：
15
通讯作者：
Chen Ning
中科院分区：
文献类型：
--
作者：
Zhang Xingxing;Wang Yaofeng;Morales-Martinez Roser;Zhong Jun;de Graaf Coen;Rodriguez-Fortea Antonio;Poblet Josep M.;Echegoyen Luis;Feng Lai;Chen Ning
锕系元素-锕系元素键的性质长期以来引起了相当大的关注，特别是最近的理论研究表明，三键和五键键应该是可能的，但实验上知之甚少。富勒笼内的锕系元素-锕系元素键也被提出，但它们的存在一直受到理论家的激烈争论。尽管有各种理论争论，但双金属锕系内腔富勒烯的关键实验数据从未获得过。本文报道了一种双金属锕系内嵌金属富勒烯（EMF）的合成和分离，网址：U2@C80。通过质谱、单晶x射线晶体学、紫外-可见-近红外光谱、拉曼光谱、循环伏安法和x射线吸收光谱（XAS）对该化合物进行了全面表征。单晶x射线晶体学分析明确地将分子结构分配给U2@Ih(7)-C80。特别是，晶体学数据显示，在c80笼内的弱U-U键的U-U距离为3.46 ~ 3.79 Å，比之前预测的3.9 Å要短。XAS结果显示，被困在富勒烯笼内的U原子的形式电荷为+3，这与计算和晶体学研究中指定的六阴离子碳笼（Ih-C80）6 -相一致。理论研究证实了U-U键相互作用的存在，并表明U2@Ih(7)- c80中的弱U-U键在还原时增强，在氧化时减弱。U2@Ih(7)- c80的综合表征以及实验数据与理论研究的总体吻合，为富勒烯笼内锕系元素金属-金属键的相互作用提供了实验证据和更深入的理解。
The nature of actinide–actinide bonds has attracted considerable attention for a long time, especially since recent theoretical studies suggest that triple and up to quintuple bonds should be possible, but little is known experimentally. Actinide–actinide bonds inside fullerene cages have also been proposed, but their existence has been debated intensively by theoreticians. Despite all the theoretical arguments, critical experimental data for a dimetallic actinide endohedral fullerene have never been obtained. Herein, we report the synthesis and isolation of a dimetallic actinide endohedral metallofullerene (EMF), U2@C80. This compound was fully characterized by mass spectrometry, single crystal X-ray crystallography, UV–vis–NIR spectroscopy, Raman spectroscopy, cyclic voltammetry, and X-ray absorption spectroscopy (XAS). The single crystal X-ray crystallographic analysis unambiguously assigned the molecular structure to U2@Ih(7)-C80. In particular, the crystallographic data revealed that the U–U distance is within the range of 3.46–3.79 Å, which is shorter than the 3.9 Å previously predicted for an elongated weak U–U bond inside the C80cage. The XAS results reveal that the formal charge of the U atoms trapped inside the fullerene cage is +3, which agrees with the computational and crystallographic studies that assign a hexaanionic carbon cage, (Ih-C80)6–. Theoretical studies confirm the presence of a U–U bonding interaction and suggest that the weak U–U bond in U2@Ih(7)-C80is strengthened upon reduction and weakened upon oxidation. The comprehensive characterization of U2@Ih(7)-C80and the overall agreement between the experimental data and theoretical investigations provide experimental proof and deeper understanding for actinide metal–metal bonding interactions inside a fullerene cage.