新型内嵌混合金属氮化物原子簇富勒烯的合成、结构与性质*

内嵌混合金属氮化物原子簇富勒烯的发现极大地扩展了内嵌富勒烯家族。内嵌混合金属氮化物原子簇富勒烯是一类新型的内嵌富勒烯,其内嵌物为由2-3种不同的金属组成的氮化物原子簇。本文首先介绍了新型内嵌混合金属氮化物原子簇富勒烯的发现、合成和分离方法,并对目前所分离出来的内嵌混合金属氮化物原子簇富勒烯进行了分类。然后总结了目前所报导的内嵌混合金属氮化物原子簇富勒烯的结构表征手段,对于不同的内嵌混合金属氮化物原子簇富勒烯的分子结构分别进行了阐述。最后着重讨论了内嵌混合金属氮化物原子簇富勒烯的特殊电子性质以及物理和化学性质。本文还对内嵌混合金属氮化物原子簇富勒烯潜在的应用前景作了展望,在内嵌具有不同物理性质的两到三种金属原子的基础上,所形成的内嵌混合金属氮化物原子簇富勒烯有可能兼具不同金属原子各自的性质,从而成为多功能综合的功能材料。     

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。     

钆基富勒烯磁共振成像分子影像探针的研究进展

含有顺磁性金属钆离子及钆团簇的内嵌金属富勒烯(如Gd@C82,Gd@C60和Gd3 N@C80)及其衍生物是一类高效的MRI分子影像探针,其造影效率远优于传统钆基螯合物造影剂.重要的是,碳笼的高度稳定性保护了内嵌团簇,使之免受体内代谢物质的进攻和防止了外泄,从而大大提高了其生物安全性.同时,碳笼还是其它生物活性物质或分子影像探针的有效载体,易赋予其多功能性,从而提高疾病检测的灵敏度和准确性.本文介绍了多种钆内嵌金属富勒烯分子影像探针的研究进展,讨论了内嵌金属团簇和笼外化学修饰对其弛豫性能的影响,以及不同的功能基团对其生物相容性和动物体内分布的影响,并展望了其兼具多功能分子影像探针载体的应用前景.     

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.     

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.     

内嵌金属碳氮化物团簇富勒烯的稳定性与生成机理

对新结构富勒烯金属包合物的探索是富勒烯领域中的研究重点。本文从内嵌团簇与富勒烯碳笼尺寸匹配的角度出发,对基于金属碳氮化物团簇的新结构富勒烯金属包合物进行了研究。通过量子化学计算研究了M_3NC团簇(M=Y,La,Gd)内嵌在D_2(186)-C_(96)和D_2(35)-C_(88)分子中所形成包合物的稳定性和电子结构,发现富勒烯碳笼接受内嵌团簇转移的六个电子形成了稳定结构。结合文献已报道过的Sc_3NC@I_h(7)-C_(80)分子,阐明了M_3NC团簇与富勒烯碳笼之间的尺寸匹配效应,并发现D_2(186)-C_(96)、D_2(35)-C_(88)和I_h(7)-C_(80)三种富勒烯碳笼均具有五元环均匀分布的结构特点。我们对富勒烯之间的转变路径进行了研究,提出了不含Stone-Wales异构化过程的富勒烯直接生成机理,即可以通过增加碳原子的过程使五元环重排,在保持稳定性结构单元的同时转变为更大碳笼。     

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。     

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。     

Sm金属富勒烯的高效提取和电化学性质研究

在金属富勒烯 [1]的形成过程中 ,存在从金属到碳笼的电子转移 .La系金属富勒烯中 ,金属原子转移 2或 3个电子给碳笼形成 + 2或 + 3价的金属离子和带有大量负电荷的碳笼 .尽管如此 ,金属富勒烯仍具有良好的接受电子的能力 [2 ,3] .大多数的 La系金属富勒烯 ( Y,La,Ce,Pr,Nd,Gd,Tb,Dy,Ho,Er,L u)的电化学方法研究表明 ,它们可以接受 5到 6个电子 ,但是 ,Sm的金属富勒烯的氧化还原性质尚未见报道 ,其主要原因是 Sm金属富勒烯的合成产率低 ,仅是 La金属富勒烯的 7% ,从而使得其分离非常困难 ,需要通过多步 HPLC循环才能得到 [4 ,5] ,高…     

内嵌金属富勒烯Sc2S@C86的结构和性质

金属硫化物富勒烯是一类结构新奇的化合物,阐释其结构和性质是当前的重要研究任务。本文采用密度泛函理论(DFT)方法,系统研究了质谱实验已经检测到的内嵌金属富勒烯Sc₂S@C₈₆的结构和性质。结果显示,能量最低的异构体是Sc₂S@C₈₆:63751(独立五元环规则(IPR)-9),该碳笼与已报道的Sc₂C₂@C₈₆的碳笼一样;其次是non-IPR Sc₂S@C₈₆:63376。自然键轨道(NBO)和分子中原子理论(AIM)分析显示,内嵌团簇与碳笼间存在电荷转移相互作用和共价作用。温度效应计算显示,高温时Sc₂S@C₈₆是多个异构体共存的。为了对将来实验结构测定提供参考,本文提供了能量最低的两个异构体的红外光谱图。     

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。     

Endohedral zintl ions: intermetalloid clusters

Tetrels can be regarded as most promising candidates for the construction of larger clusters. Recent examples have shown that larger clusters are particularly stable if they contain interstitial atoms (e.g. [Pt@Pb12]2-). Many salts of the polyhedral anions are soluble, but a number of examples-usually those with higher charges-occur only as quasi-discrete units in saltlike crystals (Zintl phases) or as building blocks in intermetallic phases. In this Minireview, the chemistry of intermetalloid clusters is reviewed with reference to the endohedral Zintl ions, Zintl phases, and polyhedral building blocks of intermetallic compounds, including heteroatomic species in the gas phase. We focus on selected examples and discuss the new findings in the context of recent advances in the field of metalloid clusters and (endohedral) fullerenes and fullerides.     

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.     

Evaluation of bonding,electron affinity,and optical properties of M@C28 (M = Zr,Hf, Th,and U): Role of d‐ and f‐orbitals in endohedral fullerenes from relativistic DFT calculations

The experimentally characterized endohedral metallic fullerenes involving the small C₂₈ cage, has shown to be able to encapsulate zirconium, hafnium, and uranium atoms, among other elements. Here, we explore the formation and nature of concentric bonds from purely d‐ to f‐block elements, given by Zr, Hf, and uranium, along a borderline metal between such blocks, thorium. We explore the interplay of d‐ and f‐orbitals in the chemistry of the early actinides, where the features of a d‐ or f‐block metal can be mixed. Our results indicate that the bonding of Th@C₂₈ involves contributions from both d‐ and f‐type bonds, as characteristic of this early actinide element. Even uranium in U@C₂₈, also exhibits a contribution from d‐type bonds in addition to its relevant f‐block character. Electron affinity and optical properties were evaluated to gain more insights into the variation of these molecular properties in this small endohedral fullerene, along Zr, Hf, Th, and U. The current results, allows to unravel the role of (n − 1)d and (n − 2)f orbitals in confined elements ranging from d‐ to f‐blocks, which can be useful to gain a deeper understanding of the bonding situation in other endohedral species. © 2016 Wiley Periodicals, Inc.     

Chemistry of fullerenes, novel allotropic modifications of carbon

The currently available data on the structure and reactivity of fullerenes, including the formation of metal complexes (including optically active ones) with fullerenes as ligands, are briefly surveyed. The properties and reactions of fullerenyl radicals and endohedral complexes are considered. The review is based on the report of the same name delivered at the XVI Mendeleev Congress (May 28, 1988, St. Petersburg). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1211–1218, July, 1999.     

2‐Aminoethanol Extraction as a Method for Purifying Sc3N@C80 and for Differentiating Classes of Endohedral Fullerenes on the Basis of Reactivity

Extraction with 2‐aminoethanol is an inexpensive method for removing empty cage fullerenes from the soluble extract from electric‐arc‐generated fullerene soot that contains endohedral metallofullerenes of the type Sc₃N@C_2n (n=34, 39, 40). Our method of separation exploits the fact that C₆₀, C₇₀, and other larger, empty cage fullerenes are more susceptible to nucleophilic attack than endohedral fullerenes and that these adducts can be readily extracted into 2‐aminoethanol. This methodology has also been employed to examine the reactivity of the mixture of soluble endohedral fullerenes that result from doping graphite rods used in the Krätschmer–Huffman electric‐arc generator with the oxides of Y, Lu, Dy, Tb, and Gd. For example, with Y₂O₃, we were able to detect by mass spectrometry several new families of endohedral fullerenes, namely Y₃C₁₀₈ to Y₃C₁₂₆, Y₃C₁₀₇ to Y₃C₁₂₅, Y₄C₁₂₈ to Y₄C₁₄₆, that resisted reactivity with 2‐aminoethanol more than the empty cage fullerenes and the mono‐ and dimetallo fullerenes. The discovery of the family Y₃C₁₀₇ to Y₃C₁₂₅ with odd numbers of carbon atoms is remarkable, since fullerene cages must involve even numbers of carbon atoms. The newly discovered families of endohedral fullerenes with the composition M₄C_2n (M=Y, Lu, Dy, Tb, and Gd) are unusually resistant to reaction with 2‐aminoethanol. Additionally, the individual endohedrals, Y₃C₁₁₂ and M₃C₁₀₂ (M=Lu, Dy, Tb and Gd), were remarkably less reactive toward 2‐aminoethanol.     

Zur Bildung von Fullerenen und endohedralen Metallofullerenen: Darstellung im Hochfrequenzofen

Formation of Fullerenes and Endohedral Metallofullerenes: Preparation in a Radiofrequency Furnace A thermodynamic analysis of the reaction of formation is presented for C₆₀. The alternative route for the preparation of fullerenes by evaporating carbon in a RF-furnace is described. This process is characterized by its broad variability and by comparatively mild conditions which, in addition, may be measured and controlled rather precisely. Thus, it offers favorite facilities for the production of soots with high contents of fullerenes and endohedral fullerenes. So far, LaC₈₂ could be extracted using toluene.     

Blending Non‐Group‐3 Transition Metal and Rare‐Earth Metal into a C80 Fullerene Cage with D5h Symmetry

Rare‐earth metals have been mostly entrapped into fullerene cages to form endohedral clusterfullerenes, whereas non‐Group‐3 transition metals that can form clusterfullerenes are limited to titanium (Ti) and vanadium (V), and both are exclusively entrapped within an I_h‐C₈₀ cage. Non‐Group‐3 transition‐metal‐containing endohedral fullerenes based on a C₈₀ cage with D_5h symmetry, V_xSc_3?xN@D_5h‐C₈₀ (x=1, 2), have now been synthesized, which exhibit two variable cluster compositions. The molecular structure of VSc₂N@D_5h‐C₈₀ was unambiguously determined by X‐ray crystallography. According to a comparative study with the reported Ti‐ and V‐containing clusterfullerenes based on a I_h‐C₈₀ cage and the analogous D_5h‐C₈₀‐based metal nitride clusterfullerenes containing rare‐earth metals only, the decisive role of the non‐Group‐3 transition metal on the formation of the corresponding D_5h‐C₈₀‐based clusterfullerenes is unraveled.