内嵌金属富勒烯的笼外化学修饰

内嵌金属富勒烯以其独特的结构和新奇的性质吸引了众多科学家的目光,对它们进行笼外化学修饰是最近十年来新兴的研究热点,这对于考察内嵌金属富勒烯的结构及化学物理性质并拓宽其应用范围具有重要意义。本文将内嵌金属富勒烯与各种底物的不同作用分类,以反应类型为线索,详细概括了已发表的内嵌金属富勒烯的各种笼外化学反应,包括各种环化反应、内嵌金属富勒烯与杯芳烃及冠醚的自组装、单键相连的衍生物、水溶性衍生物以及用内嵌金属富勒烯填充碳纳米管等。在对各种化学反应阐述的同时,对内嵌金属富勒烯的可能应用也进行了总结,并提出了自己的看法。     

内嵌富勒烯的研究进展

内嵌富勒烯由于其结构新颖以及独特而优异的性质在国际上引起持续而广泛的关注,成为近年来的研究热点之一.目前已经研究发现的内嵌富勒烯多达近百种,从惰性气体到碱土金属再到稀土元素都已被成功地嵌入到不同尺寸的碳笼中.其中金属离子或含金属的离子簇内嵌入富勒烯碳笼形成的内嵌金属富勒烯,以其种类丰富、结构多样成为内嵌富勒烯的主要研究对象.本文就近年来研究报道的种类繁多的内嵌富勒烯按其内嵌物类型进行归纳阐述,为今后开发更多新型的内嵌富勒烯提供一定的参考.     

三金属氮化物富勒烯中富勒烯笼和内嵌团簇的尺寸效应

内嵌金属富勒烯是指金属原子或其团簇内嵌于碳笼之中而形成的复合结构.实验和理论研究都表明内嵌金属原子或团簇对碳笼的电荷转移作用在这类分子中是普遍存在的,并且电荷转移作用能够稳定化原本高度活性的碳笼.三金属氮化物富勒烯(trimetallic nitride fullerenes,TNFs)因其新奇的结构和性质吸引了广泛的研究兴趣.研究者已经对Sc3N@C68,Sc3N@C78和Sc3N@C80进行了广泛而深入的研究并阐明了它们的结构;而且,三金属氮化物团簇(M3N,M=Sc,Y,La等)在各种碳中的稳定化机理已经被阐明,即能够嵌入氮化物团簇的碳笼是那些LUMO+3与LUMO+4能级能量差大的碳笼.对于含有更重的内嵌团簇的TNFs,目前已经取得相当的研究进展,然而仍然有很多未解之谜等待揭开.如:为什么烟灰中Sc3N@C2n,Y3N@C2n和La3N@C2n(n=34,39和40)的产量戏剧性地下降?三金属氮化物M3N@C2n中,电荷转移相互作用像单金属内嵌富勒烯M@Cn中的情况一样吗?为了揭开上述未解之谜,我们对M3N@C80进行系统研究的基础上(ChemPhysChem2006,7:1306),通过密度函数理论方法,对M3N@C2n(n=34,39,40)进行了更广泛更深入的研究.结果表明,对于C68-6140,金属原子位于五元环-五元环共边(B55)的前面;对于C78-5,金属原子位于六元环-六元环共边(B66)的前面;对于C80-7,Sc原子位置不固定,而Y、La原子位于六元环(R6)的前面.Sc3N在所有考虑的碳笼内都是平面的,Y3N在C68和C78中是微弱锥化的,然而在C80-Ih中是平面的;相反,La3N在所有碳笼中都是锥化的.总之,内嵌团簇趋向于在碳笼中形成具有最大金属-金属(M-M)距离的结构,以便于张力能得到最大限度的释放.内嵌锥形团簇的那些碳笼与相应的富勒烯笼比较起来,结构上发生了重大的变形,此种情况下相应分子中存在重要的M-C以及M-M排斥力,相应的分子是不稳定的.对优化后的M3N@C2n的结构分析表明,Y-Y/Y-N和La-La/La-N距离都分别小于自由态Y3N、La3N中的M-M/M-N距离.这些结构中,金属原子与碳笼的成键特性或内嵌团簇与碳笼之间的分子轨道相互作用都是次要的.对于较小的碳笼和较大的内嵌团簇形成的体系,首先满足的应该是几何尺寸上的要求.这些结果清楚地表明,内嵌团簇尺寸较大的三金属氮化物富勒烯中存在重大的M-M以及M-C排斥相互作用并随着碳笼的增大而减小.这些计算结果揭示了内嵌团簇和碳笼的尺寸对TNFs的结构和稳定性的影响,能够良好地解释M3N在碳笼中的位置以及M3N@C2n在产量上的差异并能够为这类物质的结构测定、结构-性质关系阐释提供重要的参考价值.     

金属氮化物富勒烯MSc_2N@C_(76)的计算研究

内嵌金属富勒烯是一类具有新奇性质的富勒烯基化合物.最近,含有七元环的非经典内嵌金属富勒烯被实验报道.然而,因结构的多样性和计算量的挑战性,目前尚无有关非经典内嵌金属富勒烯的系统计算研究.本文采用密度泛函理论方法和拓展的螺旋算法,系统考察了C_(76)的经典结构和非经典结构的内嵌金属氮化物富勒烯MSc_2N@C_(76)(M=Sc,Y,La).结果显示,非经典内嵌金属富勒烯与经典内嵌金属富勒烯是竞争性的,且它们之间可以通过Stone-Wales旋转或C_2插入、挤出而实现相互转化;非经典富勒烯在内嵌金属富勒烯的形成过程中发挥了重要的作用.     

富勒烯合成化学研究进展

富勒烯是一类由12个五元环和若干六元环组成的笼状分子, 自20世纪80年代中期被发现以来就以其独特的结构和新奇的性质而成为科学界研究的热点, 25年来, 无论在基础研究还是在实际应用领域都有了长足的进步, 人们在发展富勒烯合成新方法和寻找富勒烯新结构方面做了大量的工作。本文对富勒烯的各种宏量合成方法进行了回顾, 并概述了迄今已发表的60余种富勒烯新结构,包括各种富勒烯空笼、内嵌富勒烯、富勒烯笼外修饰衍生物及氮杂富勒烯等结构。     

15N同位素标记的金属氮化物内嵌富勒烯的合成与表征

利用电弧放电法制备了¹⁵N同位素标记的金属氮化物内嵌富勒烯. 制备过程中使用¹⁵NH₄Cl作为固体氮源, 基于电弧放电方法在氦气气氛中将石墨、金属钪和¹⁵NH₄Cl高温原子化, 合成得到Sc₃¹⁵N@C₈₀和Sc₃¹⁵N@C₇₈. 利用高效液相色谱法进行分离纯化, 并通过质谱、紫外可见吸收光谱和核磁共振碳谱表征了Sc₃¹⁵N@C₈₀, 验证了¹⁵N的成功标记, 还表明合成的Sc₃¹⁵N@C₈₀具有I_h-C₈₀碳笼. 所制备的¹⁵N标记的金属氮化物内嵌富勒烯中含有98%以上的¹⁵N同位素, 将拓展金属富勒烯材料在同位素示踪等领域的应用.     

富勒烯金属包合物的研究进展*

本文介绍了富勒烯金属包合物的发现、意义、合成和提取分离方法以及各种表征手段, 介绍了对富勒烯金属包合物的电子结构和物理化学性质进行的各种研究。     

衬底对N@C60分子电子自旋共振谱的影响

N@C₆₀内嵌富勒烯是一种在量子科技领域有较高应用前景的分子。科学家们设计了一系列以内嵌富勒烯分子为基本量子单元的量子计算机模型,而构筑这样的模型具有极高的挑战。其中,由于内嵌富勒烯分子阵列的制备通常需要合适的衬底,而衬底与分子之间的相互作用会影响甚至破坏内嵌N原子的自旋信号。因此研究和理解衬底与内嵌富勒烯分子的相互作用具有重要的意义。本文制备了高质量的N@C₆₀分子,并采用扫描隧道显微镜对其在Au(111)表面的结构及电子态进行表征。通过对比N@C₆₀分子在Au(111)、Si(111)、SiO₂表面的电子自旋共振(ESR)信号随时间及其抽真空处理的变化,表明Au原子的核自旋与内嵌N原子的电子自旋的耦合作用是Au(111)表面N@C₆₀单分子层的ESR谱中内嵌N原子的信号衰减的主要原因。     

笼内金属富勒烯研究进展

回顾了十年来关于笼内金属富勒烯的研究工作，详细介绍了笼内金属富勒烯的各种合成方法、提取手段以及分离方法，阐明了笼内金属富勒烯的电子结构并给出了各类方法对其结构、性质研究取得的成果，最后指出了笼内金属富勒烯的研究前景与应用潜力。     

金属富勒烯包合物

金属富勒烯包合物是目前国际上富勒烯化学研究的热点课题之一。近几年来，金属富勒烯包合物在制备，分离，结构及性质上的研究都取得了一定的进展。文章对近年来金属包合物的研究进行综合评述与分析。     

Structural interconnections and the role of heptagonal rings in endohedral trimetallic nitride template fullerenes

Recent experiments indicate that fullerene isomers outside the classical definition can also encapsulate metallic atoms or clusters to form endohedral metallofullerenes. Our systematic study using DFT calculations, suggests that many heptagon‐including nonclassical trimetallic nitride template fullerenes are similar in stability to their classical counterparts, and that conversion between low‐energy nonclassical and classical parent cages via Endo–Kroto insertion/extrusion of C₂ units and Stone–Wales isomerization may facilitate the formation of endohedral trimetallic nitride fullerenes. Close structural connections are found between favored isomers of trimetallic nitride template fullerenes from C₇₈ to C₈₂. It appears that the lower symmetry and local deformations associated with introduction of a heptagonal ring favor encapsulation of intrinsically less symmetrical mixed metal nitride clusters. © 2016 Wiley Periodicals, Inc.     

Fullerenes encaging metal clusters--clusterfullerenes

Clusterfullerenes represent a novel branch of endohedral fullerenes, which are characterized by a robust fullerene cage with metal clusters encaged in its hollow. Since the discovery of nitride clusterfullerenes (NCFs) in 1999, the family of clusterfullerenes has been significantly expanded within the past decade, with new members including carbide clusterfullerenes (CCFs), hydrocarbide clusterfullerenes (HCCFs), oxide clusterfullerenes (OCFs), sulfide clusterfullerenes (SCFs), and carbonitride clusterfullerenes (CNCFs). We first present the classification of clusterfullerenes and list all the clusterfullerenes reported to date. For each type of clusterfullerenes, we review in detail their synthesis, separation, intriguing molecular structures and properties. For NCFs, as the first and most important clusterfullerenes, we point out the significance of their discovery and focus on their new synthesis and separation methods as well as the new advances. Finally the potential applications of clusterfullerenes are addressed. We conclude that clusterfullerenes appear to be the fastest growing family of endohedral fullerenes up to now, and emphasize the importance of exploring new structures and chemical functionalizations of clusterfullerenes.     

Endohedral clusterfullerenes--playing with cluster and cage sizes

The family of endohedral fullerenes was significantly enlarged within the past six years by the clusterfullerenes containing structures like the M(2)C(2) carbides and the M(3)N nitrides. While the carbide clusters are generated under the standard arc burning conditions according to the stabilisation energy the nitride clusterfullerene type is formed by varying the composition of the cooling gas atmosphere in the arc burning process. The special situation in nitride clusterfullerene synthesis is described in detail and the optimum conditions for the production of nitride clusterfullerenes as the main product in fullerene synthesis are discussed. A review of new nitride clusterfullerenes reported recently is given summarizing the structures, properties and the stability of metal nitride clusterfullerenes. It is shown that all cages with even carbon atoms of C(68) and beyond are available as endohedral nitride clusterstructures. Furthermore the nitride clusterfullerenes are that class of endohedral fullerenes forming the largest number of non-IPR structures. Finally the prospects of this evolving field are briefly discussed taking the superior stability of these endohedral clusterfullerenes into account.     

富勒烯的化学研究进展

本文评述了富勒烯化学研究的新进展, 从[ 60 ]、[ 70 ]富勒烯的化学修饰、富勒烯金属包合物、掺杂富勒烯、碳纳米管以及富勒烯的化学合成等几个方面着重介绍了国际上富勒烯研究的热点, 对进一步研究的方向进行了讨论。     

An Expanded Family of Dysprosium–Scandium Mixed‐Metal Nitride Clusterfullerenes: The Role of the Lanthanide Metal on the Carbon Cage Size Distribution

A large family of dysprosium–scandium (Dy‐Sc) mixed‐metal nitride clusterfullerenes (MMNCFs), Dy_xSc_3?xN@C_2n (x=1, 2, 2n=68, 70, 76–86) have been successfully synthesized and isolated. Among these, the C₇₀ and C₈₂‐based MMNCFs are two new cages that have never been isolated for MMNCFs. Synthesis of Dy_xSc_3?xN@C_2n was accomplished by the “selective organic solid” route using guanidinium thiocyanate as the nitrogen source, and their isolation was fulfilled by recycling HPLC. UV/Vis‐NIR spectroscopic study indicates that almost all Dy_xSc_3?xN@C_2n MMNCFs are kinetically stable fullerenes with optical band gaps beyond 1 eV. This feature is distinctly different to their counterparts Dy₃N@C_2n (78≤2n≤88), whose for optical band‐gaps are below 1 eV for relatively large cages such as C₈₄ and C₈₆. An FTIR spectroscopic study in combination with DFT calculations enables reasonable assignments of the cage isomeric structures of all isolated Dy_xSc_3?xN@C_2n (x=1, 2, 2n=68, 70, 76–86) MMNCFs. The carbon cage size distribution of Dy_xSc_3?xN@C_2n (2n=68, 70, 76–86) is compared to the reported Dy₃N@C_2n (78≤2n≤8) homogeneous NCF and Dy_xSc_3?xN@C_2n (78≤2n≤88) MMNCF families, revealing that the medium‐sized Dy metal plays a crucial role on the expanded cage size distribution of MMNCFs. As a result, Dy_xSc_3?xN@C_2n MMNCFs are the largest MMNCF family reported to date.     

Salvaging Reactive Fullerenes from Soot by Exohedral Derivatization

The awesome allotropy of carbon yields innumerable topologically possible cage structures of molecular carbon. This field is also related to endohedral metallofullerenes constructed by metal‐atom encapsulation. Stable and soluble empty fullerenes and endohedral metallofullerenes are available in pure form in macroscopic amounts from carbon arc production or other physical processes followed by extraction and subsequent chromatographic separation. However, many other unidentified fullerene species, which must be reactive and insoluble in their pristine forms, remain in soot. These “missing” species must have extremely small HOMO–LUMO gaps and may have unconventional cage structures. Recent progress in this field has demonstrated that reactive fullerenes can be salvaged by exohedral derivatization, which can stabilize the reactive carbon cages. This concept provides a means of preparing macroscopic amounts of unconventional fullerenes as their derivatives.     

Geometrical and Electronic Rules in Fullerene‐Based Compounds

The discovery of buckminsterfullerene C₆₀ opened up a new scientific area and stimulated the development of nanoscience and nanotechnology directly. Fullerene science has since emerged to include fullerenes, endohedral fullerenes (mainly metallofullerenes), exofullerenes, and carbon nanotubes as well. Herein, we look back at the development of fullerene science from the perspective of epistemology by highlighting the proposed main rules or criteria for understanding and predicting the structures and stability of fullerene‐based compounds. We also point out that a rule or criterion may contribute significantly to the corresponding discipline and suggest that two unsolved issues in fullerene science are the addition patterns of fullerene derivatives and the structures and stability of nonclassical fullerenes.     

Chemical reactivity of D3h C78 (metallo)fullerene: regioselectivity changes induced by Sc3N encapsulation

We report here for the first time a full comparison of the exohedral reactivity of a given fullerene and its parent trinitride template endohedral metallofullerene. In particular, we study the thermodynamics and kinetics for the Diels-Alder [4 + 2] cycloaddition between 1,3-butadiene and free D3h'-C78 fullerene and between butadiene and the corresponding endohedral D3h-Sc3N@C78 derivative. The reaction is studied for all nonequivalent bonds, in both the free and the endohedral fullerenes, at the BP86/TZP//BP86/DZP level. The change in exohedral reactivity and regioselectivity when a metal cluster is encapsulated inside the cage is profound. Consequently, the Diels-Alder reaction over the free fullerene and the endohedral derivative leads to totally different cycloadducts. This is caused by the metal nitride situated inside the fullerene cage that reduces the reactivity of the free fullerene and favors the reaction over different bonds.