C~4~0, C~4~0^+, Nb@C~4~0^+, NbC~3~9^+, Nb@C~4~0H~4^+的 量子化学研究

用量子化学从头计算方法研究了C~4~0,C~4~0^+,Nb@C~4~0^+,NbC~3~9^+,Nb@C~4~0H~4^+的几何构型、电子结构和C~2~8一样,C~4~0(T~d)基态也为^5A~2态,笼骨架上具有四个悬挂键。计算结果表明C~4~0和C~4~0^+比NbC~3~9^+和Nb@C~4~0^+稳定,与实验结果一致。     

C~6~0^2^-单态和三态的结构和光谱性质

用INDO系列方法对C~6~0^2^-单态和三态分别进行了几何构型优化, 得到D~2~h对称性的构型, 表明C~6~0^2^-确实发生了Jahn-Teller畸变, 导致双键变长, 形成15种键, 9种不等同碳原子, 其额外负电荷主要分布在赤道附近, 以此构型为基础,计算了C~6~0^2^-的电子光谱, 与实验值基本一致, 对光谱进行了理论指认, 说明了光谱红移的原因。     

C~6~0^3^-的Jahn-Teller变形、电子结构和光谱性质的理论研究

本文用INDO系列方法对C~6~0^3^-进行了几何构型优化, 得到D~2~h构型, 表明C~6~0^3^-确实发生了Jahn-Teller变形, 导致单键变短, 双键变长, 其额外负电荷和单电子主要分布在赤道附近。以此构型为基础, 计算其电子吸收光谱, 与实验值基本吻合, 在对光谱进行理论指认的同时, 讨论了光谱红移的原因。     

富勒烯C~6~0与二茂铁酮亚胺电荷转移相互作用的研究

C~6~0与三种二茂铁酮亚胺η^5-C~5H~5Fe[C~5H~4C(CH~3)=N-C~6H~4R-p]-η^5(1a R=H,1bR=CH~3,1c R=OCH~3)在甲苯和室温下可发生电荷转移相互作用形成三种电荷转移配合物η^5-C~5H~5Fe[C~5H~4C(CH~3)=N-C~6H~4R-p]-η^5/C~6~0 (2a R=H,2b R=CH~3,2c R=OCH~3)。通过紫外光谱证实了它们的存在,并用Benesi-Hildebrand方程求出了2a、2b和2c的电荷转移平衡常数分别为0.769、0.928和2.353mol^-^1·dm^3。鉴于它们远大于普通有机胺与C~6~0形成的电荷转移配合物的平衡常数,因此可认为在2a～2c中存在着由二茂铁核及亚胺基向C~6~0的双重电荷转移相互作用。     

TiP2^+,TiP4^+,Ti2P4^+二元团簇的理论研究

利用含有电子相关效应校正的密度泛函理论DFT中的B3LYP方法,选择LANL2DZ双ξ基组,并考虑极化函数,对TiP2^+,TiP4^+,Ti2P4^+二元团簇各种可能存在的几何构型及电子结构进行了密度泛函理论研究,得到了TimPn^+二元团族的最稳定构型,其中TiP2^+的最稳定构型为C2v对称性的三角形,TiP4^+的最稳定构型亦具有C2v对称性,Ti2P4^+的最稳定构型为具有D2d对称性的共边双四面体,所得构型很好地说明了激光光解的实验结果。     

C~1~2~0O的分子结构和光谱性质的理论研究

用INDO系列方法对双笼氧化物C~1~2~0O进行了理论研究,结果表明:双笼氧化物C~1~2~0O的形成缓解了C~6~0O中环氧三元环的角张力,并形成了呋喃型五元环将两碳笼连接在一起。两碳笼的直接键连使两笼距离较近,有较弱的相互作用,但仍各自表现一定的独立性,C~1~2~0O可发生分解生成新的化合物,C~1~2~0O的电子光谱与母体分子C~6~0相似。     

新型二维草酸根桥联配合物 {[Cu(en)~2]~4[KFe(C~2O~4)~3]~4}~n的合成、结构 和磁性

合成了一个新型草酸根桥联的二维配合物{[Cu(en)~2]~4[KFe(C~2O~4)~3]~4}~n,并进行了晶体结构测试和磁性研究。晶体结构分析显示:K^+离子为罕见的八配位环境,2个C~2O~4^2^-和2个或1个K^+离子长程桥联2个Fe^Ⅲ离子,形成一个二维网状的[KFe(C~2O~4)~3]~n^2^n^-骨架,[Cu(en)~2]^2^+单元通过(en)N-H...O(C~2O~4)氢键与[KFe(C~2O~4)~3]~n^2^n^-骨架连接。变温磁化率测量表明:Fe^Ⅲ与Fe^Ⅲ间存在着弱的磁相互作用,J=-0.17cm^-^1。     

C~6~0, C~7~0的烷基化

本文利用低价稀土化物(S~mI~2或YbI~2)与C~6~0、C~7~0及卤代烃(烯丙基溴、氯苄)的混合溶液反应,制得烯丙基化、苄基化的富勒烯。发现与C~6~0相接的苄基数可以从1到14,验证了Krusic等人的结果。此外,还发现C~6~0可以进行烯丙基化,得到(CH~2=CHCH~2)~nC~6~0(n=1-10),C~7~0可以进行苄基化,C~7~0上至少可以接13个苄基,实验证明这类反应是对富勒烯进行烷基化的一种简便、有效的方法。     

C~6~0SiH~2的结构和电子光谱的量子化学研究

用INDO系列方法研究了C~6~0SiH~2的两种结构: 一是SiH~2加在两个六元环之间的键上形成C~2~v构型; 另一是SiH~2加在一个五元环和一个六元环之间的键上形成C~s构型。从总能量和LUMO-HOMO能级差看, C~6~0SiH~2的稳定结构应是C~2~v构型, 其中桥C(15)-C(30)的键长为0.1508nm, 键序为0.9369, 说明不开环, 形成类环丙烷结构。文中计算了两种构型的电子吸收光谱和NMR谱, 此类计算是基于对C~6~0SiH~2的等电子体C~6~0O和C~6~0CH~2的研究之上, 且后两者的研究结果与实验相一致。     

异质富勒烯C~5~9Si与C~6~9Si的理论研究

利用MNDO,AM1和PM3半经验量子化学计算方法对硅杂富勒烯C~5~9Si和C~6~9Si进行了系统的理论研究.计算了稳定构型、生成热、前沿轨道能级差、电离势、电子亲和势、绝对电负性和整体硬度.结果表明,硅杂富勒烯的稳定性虽然低于全碳富勒烯,但也具有相当的稳定性.C~5~9Si的稳定性比已经合成的C~5~8X~2(X=B,N)高,C~6~9Si与C~7~0的稳定性差异也很小,因此在适宜条件下文中所讨论的硅杂富勒烯是应该能够合成的.在C~6~9Si各异构体中,取代位置在赤道的异构体具有最低的能量和最大的前沿轨道能级差,也是最稳定的异构体.与全碳勒烯C~6~0和C~7~0相比,C~5~9Si和C~6~9Si具有较小的电离势和电子亲和势,表明硅杂富勒烯容易被氧化,而被还原的难度要些,但是仍容易发生还原反应而生成负离子.因此硅原子的掺杂能够使富勒烯的氧化还原性能得以改善.C~5~9Si和C~6~9Si更容易与亲电试剂反应,而发生亲核反应的活性要相对小一些.硅杂富勒烯C~5~9Si和C~6~9Si的绝对电负性和硬度都小于相对应的全碳富勒烯,对电子的束缚力要相对小一些。     

C40,Nb@C40^＋,La@C40^＋的从头算研究

用量子化学从头算方法研究了Ｃ４０、Ｎｂ＠Ｃ４０＾＋，Ｌａ＾＠Ｃ４０＾＋的几何构型和电子结构，Ｃ４０最稳定构型具有Ｄ２对称性。Ｌａ和Ｎ原子内含于Ｃ４０笼中，形成金属夹心碳笼Ｎｂ＠Ｃ４０＾＋、Ｌａ＠Ｃ４０＾＋。Ｃ４０结合能大于Ｍ＠Ｃ４０＾＋（Ｍ＝Ｎｂ，Ｌａ）。     

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.     

Photoelectron spectroscopy and density functional calculations of CuSi(n)- (n = 4-18) clusters

We conducted a combined anion photoelectron spectroscopy and density functional theory study on the structural evolution of copper-doped silicon clusters, CuSi(n)(-) (n = 4-18). Based on the comparison between the experiments and theoretical calculations, CuSi(12)(-) is suggested to be the smallest fully endohedral cluster. The low-lying isomers of CuSi(n)(-) with n ≥ 12 are dominated by endohedral structures, those of CuSi(n)(-) with n < 12 are dominated by exohedral structures. The most stable structure of CuSi(12)(-) is a double-chair endohedral structure with the copper atom sandwiched between two chair-style Si(6) rings or, in another word, encapsulated in a distorted Si(12) hexagonal prism cage. CuSi(14)(-) has an interesting C(3h) symmetry structure, in which the Si(14) cage is composed by three four-membered rings and six five-membered rings.     

Exohedral reactivity of trimetallic nitride template (TNT) endohedral metallofullerenes

[structures: see text] Fullerenes containing a trimetallic nitride template (TNT) within the cage are a particularly interesting class of endohedral metallofullerenes. Recently two exohedral derivatives of the Sc3N@C80 fullerene have been synthesized: a Diels-Alder and a fulleropyrrolidine cycloadduct. The successful isolation, purification, and structural elucidation of these metallofullerenes derivatives have encouraged us to understand how the chemical reactivity is affected by TNT encapsulation. First of all, we predicted the most reactive exohedral sites, taking into account the double bond character and the pyramidalization angle of the C-C bonds. For this purpose, a full characterization of all different types of C-C bonds of the following fullerenes was carried out: I(h)-C60:1, D3-C68:6140, D3-Sc3N@C68, D(5h)-C70:1, D(3h')-C78:5, D(3h)-Sc3N@C78, I(h)-C80:7 and several isomers of Sc3N@C80. Finally the exohedral reactivity of these TNT endohedral metallofullerenes, via [4 + 2] cycloaddition reactions of 1,3-butadiene, was corroborated by means of DFT calculations.     

On the viability of small endohedral hydrocarbon cage complexes: X@C4H4, X@C8H8, X@C8H14, X@C10H16, X@C12H12, AND X@C16H16

Small hydrocarbon complexes (X@cage) incorporating cage-centered endohedral atoms and ions (X = H(+), H, He, Ne, Ar, Li(0,+), Be(0,+,2+), Na(0,+), Mg(0,+,2+)) have been studied at the B3LYP/6-31G(d) hybrid HF/DFT level of theory. No tetrahedrane (C(4)H(4), T(d)()) endohedral complexes are minima, not even with the very small hydrogen atom or beryllium dication. Cubane (C(8)H(8), O(h)()) and bicyclo[2.2.2]octane (C(8)H(14), D(3)(h)()) minima are limited to encapsulating species smaller than Ne and Na(+). Despite its intermediate size, adamantane (C(10)H(16), T(d)()) can enclose a wide variety of endohedral atoms and ions including H, He, Ne, Li(0,+), Be(0,+,2+), Na(0,+), and Mg(2+). In contrast, the truncated tetrahedrane (C(12)H(12), T(d)()) encapsulates fewer species, while the D(4)(d)() symmetric C(16)H(16) hydrocarbon cage (see Table of Contents graphic) encapsulates all but the larger Be, Mg, and Mg(+) species. The host cages have more compact geometries when metal atoms, rather than cations, are inside. This is due to electron donation from the endohedral metals into C-C bonding and C-H antibonding cage molecular orbitals. The relative stabilities of endohedral minima are evaluated by comparing their energies (E(endo)) to the sum of their isolated components (E(inc) = E(endo) - E(cage) - E(x)) and to their exohedral isomer energies (E(isom) = E(endo) - E(exo)). Although exohedral binding is preferred to endohedral encapsulation without exception (i.e., E(isom) is always exothermic), Be(2+)@C(10)H(16) (T(d)(); -235.5 kcal/mol), Li(+)@C(12)H(12) (T(d)(); 50.2 kcal/mol), Be(2+)@C(12)H(12) (T(d)(); -181.2 kcal/mol), Mg(2+)@C(12)H(12) (T(d)(); -45.0 kcal/mol), Li(+)@C(16)H(16) (D(4)(d)(); 13.3 kcal/mol), Be(+)@C(16)H(16) (C(4)(v)(); 31.8 kcal/mol), Be(2+)@C(16)H(16) (D(4)(d)(); -239.2 kcal/mol), and Mg(2+)@C(16)H(16) (D(4)(d)(); -37.7 kcal/mol) are relatively stable as compared to experimentally known He@C(20)H(20) (I(h)()), which has an E(inc) = 37.9 kcal/mol and E(isom) = -35.4 kcal/mol. Overall, endohedral cage complexes with low parent cage strain energies, large cage internal cavity volumes, and a small, highly charged guest species are the most viable synthetic targets.     

CnSi(n=49,50)的理论研究

用量子化学从头算方法研究了C_nSi(n=49,50)的各种可能的构型.结果表明,C₄₉Si为硅取代碳笼C₅₀中一个碳原子而形成的骨架硅杂碳笼,C₄₉Si与C₅₀相比稳定性较低,化学活性较高.C₅₀Si有两种类型结构:Ⅰ为外接型,Ⅱ为四连接型.计算结果表明,对C₅₀Si,外接硅型化合物更稳定,即Ⅰ为主要成分.计算结果与实验结果是一致的.     

Understanding the stabilization of metal carbide endohedral fullerenes m(2)c(2)@c(82) and related systems

We analyze the electronic structure of carbide endohedral metallofullerenes of the type Sc(2)C(2)@C(82) and study the possibility of rotation of the encapsulated Sc(2)C(2) moiety in the interior of the cage. Moreover, we rationalize the higher abundance of M(2)C(2)@C(82) (M = Sc, Y) in which the metal-carbide cluster is encapsulated in the C(3v)-C(82):8 carbon cage with respect to other carbides of the same family on the basis of the formal transfer of four electrons from the cluster to the cage and sizeable (LUMO-3)-(LUMO-2) gap in the empty cages. This rule also applies to all those endohedral metallofullerenes in which the encapsulated cluster transfers four electrons to the carbon cage as, for example, the reduced [M@C(82)](-) systems (M = group 3 or lanthanide metal ion).     

Theoretical study on the smallest endohedral metallofullerenes: TM@C20 (TM = Ce and Gd)

The structure, electronic property, and infrared spectroscopy of endohedral metallofullerenes TM@C₂₀ (TM = Ce and Gd) have been systematically investigated with the aid of the hybrid DFT‐B3LYP functional. It is found that in the endohedral metallofullerenes the average C? C bond lengths are obvious longer than those of empty cage. The frontier orbital analyses show that the endohedral metallofullerene Gd@C₂₀ has the high‐thermodynamic stability. Natural population analysis also tells us that only in the Ce@C₂₀, the Ce atom acts as an electron acceptor with the negative charges, and the 4f orbitals of Ce and Gd atoms have a significant contribution in the formation of chemical bonding. Additionally, the analyses of harmonic vibrational frequencies reveal that when the TM atoms are encapsulated into the C₂₀ cage, the strongest absorption peaks are characterized by a mixture of TM?C bending and C? C stretching vibrations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Purification of endohedral trimetallic nitride fullerenes in a single, facile step

A major hurdle hampering the development of fullerenes, endohedral metallofullerenes, and nanotubes has been the difficulty of obtaining high purity samples. Soots prepared in the usual manner via a Kr?tschmer-Huffman electric-arc generator consist of mixtures of insoluble carbonaceous materials and soluble fullerenes: C60, C70, C76, C78, C84, etc. When metals are introduced as endohedral species the complexity of the resultant soot is even greater because of the presence of multiple isomers of both the empty fullerenes and the endohedral metallofullerenes. Here, for the first time, we report that lanthanide trimetallic nitride endohedral metallofullerenes, A3N@C80 (A = lanthanide atom, e.g., Er, Gd, Ho, Lu, Sc, Tb, Tm, Y), can be obtained in pure form directly from as-prepared soots in a single facile step by taking advantage of their extraordinary kinetic chemical stability with respect to the other fullerenes in Diels-Alder reactions with a cyclopentadiene-functionalized resin. We show that careful control of conditions (stoichiometry, time, temperature) allows separation of fullerenes with different cage sizes, as well as isomeric species. Furthermore, the Diels-Alder reaction is thermally reversible, and we demonstrated that the bound empty-cage fullerenes and classical endohedral metallofullerenes can be recovered by displacement with maleic anhydride.     

Pu4+分子离子的几何构型与Jahn-Teller

It demorstrates six stable geometrical configurations of electronic states for Pu4+ using the density functional method B3LYP with relativistic effective core potentials. The most stable electronic state of Pu4+ is of the planar C2v configuration. The Jahn-Teller distortions from the configurations Pu4+(Td) and Pu4+(D4h) exist. The analysis of the relationships among these various geometrical configurations, based on the Jahn-Teller effect, vibronic interaction and the resolution of group representations, is in agreement with the calculated results.