富勒烯结构B_(80)分子静电势的理论研究

在混合密度泛函B3LYP理论下,用6-31G*基函数对富勒烯结构B80分子的3个异构体(1个具有Ih对称性,2个具有Th对称性)构型进行优化和分子静电势计算.结果表明:3个异构体球内全部为正电势,球外五元环中心所对应的区域都为负电势,B80Ih,Th(A)和Th(B)球外静电势的最大负值分别对应于20个六元环中心的B原子,五元环中心和12个六元环中心的B原子周围,它们组成了化学反应中最可能的活性点.     

DFT Studies on Non-IPR C_(68) and Endohedral Fullerene Sc_3N@C_(68)

The structures and spectra of 20 possible isomers of C78(CH2)3 have been studied by using AM1,INDO/CIS and DFT methods. The results show that the most stable isomer is 1,2,3,4,5,6-C78(CH2)3 (A) with annulene structures,where three -CH2 groups are added to the 6/6 bonds located at the same hexagon passed by the shortest axis of C78 (C2v). Compared with that of C78 (C2v),the first absorption in the electronic spectrum of C78(CH2)3 (A) is blue-shifted because of its wider LUMO-HOMO energy gap. While the IR frequencies of the C–C bonds on the carbon cage are red-shifted owing to the formation of annulene structures and the extension of the conjugated system. The chemical shifts of the carbon atoms in 13C NMR spectra are moved upfield upon the addition.     

富勒烯C72分子静电势以及Sc2@C72的理论研究

已制备出来的富勒烯都遵循分离五元环规则(IPR)。C72虽然满足五元环分离规则具有D6d对称结构,然而迄今为止还没有实现其宏观量的合成,人们称之为“遗失的碳笼”。但人们合成出了内掺金属M@C72(M=Ca,La等),证实了C72的存在[1-4]。最近用两步高性能液体色谱方法又成功地分离出La2     

Theoretical studies on the electronic structure of Ti8C12 isomers

Density functional calculation are performed to study Ti(8)C(12) isomers (T(d), C(3v), and D(2d)) in the neutral, cationic, and anionic charge states. C(3v) symmetry is found to be the most stable geometry for the neutral and anion, and the C(3v) and D(2d) isomers to be quasi-iso-energetic lowest for the cation. The electronic structure analysis show that d electron tends to be localized in the ground state. The theoretical assignment for the features in the experimental photoelectron spectra is given. All results obtained are in good agreement with the available experimental data and indicate that the C(3v) and D(2d) isomers may coexist in the photoelectron spectroscopy experiment.     

Computational study of the Stone-Wales transformation in C36

The transition of the D6h neutral and charged isomers to D2d isomers of C36 via Stone-Wales transformation has been studied by means of the hybrid density functional method (B3LYP). The results show that the transition state (TS) and reaction pathway could be identified for the rearrangement from C36-D6h to C36-D2d on the potential energy surface. We found that the neutral and charged transition states all have C2 molecular point group symmetry with the two migrating carbon atoms remaining close to the fullerene surface. The other kind of possible TS with a carbene-like structure along the stepwise reaction path does not exist as a stationary point with the density functionals utilized here. The classical barriers are 6.23 eV through the neutral TS, 6.37 eV through the anionic TS, and 6.29 eV through the cationic TS at the B3LYP/6-31G level of theory.     

On the structure and relative stability of C50 fullerenes

The complete set of 271 classical fullerene isomers of C50 has been studied by full geometry optimizations at the SAM1, PM3, AM1, and MNDO quantum-chemical levels, and their lower energy structures have also been partially computed at the ab initio levels of theory. A D(5h) species, with the least number of pentagon adjacency, is predicted by all semiempirical methods and the HF/4-31G calculations as the lowest energy structure, but the B3LYP/6-31G* geometry optimizations favor a D3 structure (with the largest HOMO-LUMO gap and the second least number of adjacent pentagons) energetically lower (-2 kcal/mol) than the D(5h) isomer. To clarify the relative stabilities at elevated temperatures, the entropy contributions are taken into account on the basis of the Gibbs energy at the HF/4-31G level for the first time. The computed relative-stability interchanges show that the D3 isomer behaves more thermodynamically stable than the D(5h) species within a wide temperature interval related to fullerene formation. According to a newly reported experimental observation, the structural/energetic properties and relative stabilities of both critical isomers (D(5h) and D3) are analyzed along with the experimentally identified decachlorofullerene C50Cl10 of D(5h) symmetry. Some features of higher symmetry C50 nanotube-type isomers are also discussed.     

富勒烯C_(36)等电子体C_(34)BN异构体的结构及其相对稳定性理论研究

用半经验的AM1和MNDO方法优化了富勒烯C_(36)的等电子体C_(34)BN所有可能 异构体的构型,分析了各异构体相对稳定性与杂原子取代位置间的关系。另外,比 较了C_(36)碳笼上同位置地取代杂原子形成的C_34BN,C_(34)B_2和C_(34)N_2间的 电子结构,并分析了C_(34)BN最稳定异构体的振动模型。结果表明以C_(36):A (D_(6h))为母体形成的最稳定C_(34)BN异构体对应于碳笼赤道位置六元环中1,4- 取代产物,而以C_(36):B(D_(2d))为母体形成的最稳定C_(34)BN异构体对应于碳笼 近赤道位置的1,2-取代产物.C_(34)BN各异构体的稳定性可能主要由体系的共轭性 质决定。前线轨道能级表明B,N原子取代所得异构体的氧化-还原活性按以下顺序 递增：C_(34)B_2相似文献   

Properties of fullerene[50] and D5h decachlorofullerene[50]: a computational study

Stimulated by the recent preparation and characterization of the first [50]fullerene derivative, decachlorofullerene[50] (Science 2004, 304, 699), we have performed a systematic density functional study on the electronic and spectroscopic properties of C(50), its anions and derivatives such as C(50)Cl(10) and C(50)Cl(12). The ground state of C(50) has D(3) symmetry with a spheroid shape, and is highly aromatic; the best D(5h)C(50) singlet is nonaromatic. Both D(3)() and D(5h)() isomers of C(50) have high electron affinities and can be reduced easily. Due to the unstable fused pentagon structural features, C(50) is chemically labile and subject to addition reactions such as chlorination, dimerization and polymerization. The equatorial pentagon-pentagon fusions of D(5h)C(50) are active sites for chemical reactions; hence, D(5h)C(50) may behave as a multivalent group. The computed IR, Raman, (13)C NMR and UV-vis spectra of the D(5h)C(50)Cl(10) molecule agree well with the experimental data. Finally, D(5h)C(50)Cl(10) is predicted to have a high electron affinity and, hence, might serve as an electron-acceptor in photonic/photovoltaic applications. The geometry and (13)C NMR chemical shifts of C(50)Cl(12) were computed to assist further isolation experiments.     

C40H2各种可能异构体稳定性的理论研究

采用AM1和PM3两种半经验方法,对D_5d对称性的C₄₀及C₄₀H₂所有可能异构体的几何构型进行了非限制对称性全优化,得到51种稳定异构体,在此基础上研究了氢的加成反应规律及本体C₄₀和最稳定及最不稳定C₄₀H₂异构体的红外光谱,讨论了影响C₄₀(D_5d)氢加成异构体稳定性及加成位置选择性的三种主要因素:(1)C₄₀本体几何结构;(2)共轭效应;(3)电荷分布影响.     

A clue to the diffuse structure in ultraviolet spectra of the GeCl2 A-X transition

Geometries, harmonic vibrational frequencies, and relative electronic energies of the two low-lying electronic states of the GeCl(2) dimer have been calculated at the CIS(D) method with a cc-pVTZ basis set. Minima corresponding to three isomers on the ground-state potential energy surface have been characterized. The most stable dimer has a dissociation energy of 0.74 eV and has a trans-(GeCl(2))(2) structure. There is also a related, less stable, cis minimum. A third, C(i) symmetry, isomer has a binding energy of 0.31 eV. It is found that this C(i) isomer has substantial dipole transition strength to the first excited singlet state of the dimer with a vertical excitation energy of 3.33 eV. The transition energy (T(0)) between this C(i) isomer and the van der Waals complex on the singlet excited state is predicted to be 4.007 eV, or a 1104 cm(-1) blueshift with respect to that of the GeCl(2) A-X transition. This finding may explain the diffuse structure which has been observed in the ultraviolet laser-induced fluorescence spectra of GeCl(2).     

C24和B12N12团簇的结构与稳定性

本文采用量子化学密度泛函理论的B3LYP/6-31G*方法,对C24和B12N12团簇的12种异构体进行了优化,并对它们的几何构型、振动频率、核独立化学位移(NICS)和结合能进行了理论探讨, 比较了C24和B12N12团簇结构的稳定性。研究表明:C24团簇的最稳定几何构型为类石墨结构d,B12N12团簇的最稳定结构为4/6笼状结构g。C24异构体的稳定性大小顺序为d > b > f > c > a > e。B12N12团簇异构体稳定性大小顺序为a > f> c> d > e >b。     

Theoretical investigation of C56 fullerene isomers and related compounds

All the 924 classical isomers of fullerene C(56) have been investigated by PM3, and some most stable isomers are refined with HCTH/3-21G and B3LYP6-31G(d) methods. D(2):003 with the least number of adjacent pentagons is predicted to be the most stable isomer at B3LYP/6-31G(d) level, while C(s):022 and C(2):049 possess nearly degenerate energies with relative energies of 0.03 and 3.90 kcal/mol, respectively. However, as to dianionic C(56)(2-) fullerene, C(2v):011 is predicted to be the most stable isomer. Investigations also show that the encapsulation of Ca atom in C(56) fullerene is exothermic and the metallofullerenes Ca@C(56) can be described as Ca(2+)@C(56)(2-). The computed relative stabilities show that the D(2):003 behaves more thermodynamically stable than other isomers in a wide temperature interval, and C(2v):011 should also be an important component. The electronic isomerization of C(56) (C(2v):011) and C(50) (D(5h):002) indicates that this phenomenon might be rather general in fullerenes and causes different properties, thus bringing about new possible applications of fullerenes. The static second-order hyperpolarizabilities of the three most stable isomers are slightly larger than that of C(60).     

Thermodynamic rearrangement synthesis and NMR structures of C1, C3, and T isomers of C60H36

The structures of three C60H36 isomers, produced by high-temperature transfer hydrogenation of C(60) in a 9,10-dihydroanthracene melt, was accomplished by 2D (1)H-detected NMR experiments, recorded at 800 MHz. The unsymmetrical C(1) isomer is found to be the most abundant one (60-70%), followed by the C(3) isomer (25-30%) and the least abundant T isomer (2-5%). All three isomers are closely related in structure and have three vicinal hydrogens located on each of the 12 pentagons. Facile hydrogen migration on the fullerene surface during annealing at elevated temperatures is believed to be responsible for the preferential formation of these thermodynamically most stable C60H36 isomers. This hypothesis was further supported by thermal conversion of C60H36 isomers to a single C(3v) isomer of C60H18.     

Infrared, Raman, and DFT vibrational spectroscopic studies of C60F36 and C60F48

IR and Raman spectra of two fluorofullerenes, C60F48 and C60F36, are thoroughly studied. Assignment of the experimental spectra is provided on the basis of density functional theory (DFT) computations. Perfect correspondence between experimental and computed spectra enabled us to confirm that the major isomer of C60F48 has D3 symmetry. It was found that as-synthesized samples of C60F36 consist mainly of C3 and C1 isomers in ca. 2:1 ratio and 2-3% of T-symmetric structures. Extensive AM1 and DFT computations have shown that all three structures are the most stable isomers of C60F36. Previous structural assignment of the C3 isomer (Gakh, A. A.; Tuinman, A. A. Tetrahedron Lett. 2001, 42, 7137-7139) was confirmed by the vibrational data.     

Investigating the chemical dynamics of the reaction of ground-state carbon atoms with acetylene and its isotopomers

We investigated the multichannel reaction of ground-state carbon atoms with acetylene, C2H2 (X1Sigmag+), to form the linear and cyclic C3H isomers (atomic hydrogen elimination pathway) as well as tricarbon plus molecular hydrogen. The experiments were conducted under single-collision conditions at three different collision energies between 8.0 kJ mol-1 and 31.0 kJ mol-1. Our studies were complemented by crossed molecular beam experiments of carbon with three isotopomers C2D2(X1Sigmag+), C2HD (X1Sigma+), and 13C2H2 (X1Sigmag+) to clarify a potential intersystem crossing (ISC), the effect of the symmetry of the reaction intermediates on the center-of-mass angular distributions, the collision energy-dependent branching ratios of the atomic versus molecular hydrogen elimination pathways, and deuterium-enrichment processes. The results are discussed in light of recent electronic structure and dynamics calculations.     

Formation, isolation, spectroscopic properties, and calculated properties of some isomers of C(60)H(36)

Isomers of C(60)H(36) and He@C(60)H(36) have been synthesized by the Birch or dihydroanthracene reduction of C(60) and isolated by preparative high-pressure liquid chromatography. (3)He, (13)C, and (1)H NMR spectroscopic properties were then determined. A comparison of experimental chemical shifts against those computed using density functional theory (B3LYP) with polarized triple- and double-zeta basis sets for He and C,H, respectively, allowed provisional assignment of structure for several isomers to be made. Theoretical calculations have also been carried out to identify low-energy structures. The transfer hydrogenation method using dihydroanthracene gives a major C(60)H(36) isomer and a minor C(60)H(36) isomer with C(3) symmetry as determined by the (13)C NMR spectrum of C(60)H(36) and the (3)He NMR spectrum of the corresponding sample of (3)He@C(60)H(36). In view of the HPLC retention times and the (3)He chemical shifts observed for the Birch and dihydroanthracene reduction products, the two isomers generated by the latter procedure can be only minor isomers of the Birch reduction. A significant energy barrier apparently exists in the dihydroanthracene reduction of C(60) for the conversion of the C(3) and C(1) symmetry isomers of C(60)H(36) to the T symmetry isomer previously predicted by many calculations to be among the most stable C(60)H(36) isomers. Many of the (1)H NMR signals exhibited by C(60)H(36) (and C(60)H(18), previously reported) are unusually deshielded compared to "ordinary" organic compounds, presumably because the unusual structures of C(60)H(36) and C(60)H(18) result in chemical shift tensors with one or more unusual principal values. Calculations clearly show a relationship between exceptionally deshielded protons beta to a benzene ring in C(60)H(18) and C(60)H(36) and relatively long C-C bonds associated with these protons. The additional information obtained from 1D and 2D (1)H NMR spectra obtained at ultrahigh field strengths (up to 900 MHz) will serve as a critical test of chemical shifts to be obtained from future calculations on different C(60)H(36) isomers.     

Structure, stability, and NMR properties of lower fullerenes C38-C50 and azafullerene C44N6

A systematic survey of the complete set of isomers of fullerenes C(38), C(40), C(42), C(44), C(46), C(48), C(50) and azafullerene C(44)N(6) is reported. All isomeric structures were optimized using first-principle density functional theory at the B3LYP/6-31G level. The isomeric structures with the lowest energies are C(38):17, C(40):38, C(42):45, C(44):75, C(44):89, C(46):109, C(48):171, and C(50):270. The ground-state structure of the azafullerene C(44)N(6) in the framework of C(50):270 has D(3) symmetry. The (13)C NMR chemical shifts and nucleus-independent chemical shifts (NICS) for the stable isomers of each fullerene are presented.     

DFT Studies on Thermal Stabilities,Electronic Structures,and ~（13）C Chemical Shifts of C_（24）O_2 Based on Fullerene C_（24）（D_6）

Quantum chemical calculations on some possible equilibrium geometries of C24O2 isomers derived from C24 (D6) and C24O have been performed using density functional theory (DFT) method. The geometric and electronic structures as well as the relative energies and thermal stabilities of various C24O2 isomers at the ground state have been calculated at the B3LYP/6-31G(d) level of theory. And the 1,4,2,5-C24O2 isomer was found to be the most stable geometry where two oxygen atoms were added to the longest carbon-carbon bonds in the same pentagon from a thermodynamic point of view. Based on the optimized neutral geometries, the vertical ionization potential and vertical electron affinity have been obtained. Meanwhile, the vibrational frequencies, IR spectrum, and 13C chemical shifts of various C24O2 isomers have been calculated and analyzed.     

Insertion of C50 into single-walled carbon nanotubes: Selectivity in interwall spacing and C50 isomers

The structures and electronic properties of nanoscale "peapods," i.e., C(50) fullerenes inside single-walled carbon nanotubes (SWCNTs), were computationally investigated by density functional theory (DFT). Both zigzag and armchair SWCNTs with diameters larger than 1.17 nm can encapsulate C(50) fullerenes exothermically. Among the SWCNTs considered, (9,9) and (16,0) SWCNTs are the best sheaths for both D(3) and D(5h) isomers of C(50), corresponding to 0.32-0.34 nm tube-C50 distances. The orientation of C(50) inside nanotubes also affects the insertion energies, which depend on the actual tube-fullerene distances. The insertion of D(3) and D(5h) isomers of C(50) is somewhat selective; the less stable D(5h) isomer can be encapsulated more favorably inside SWCNTs at same tube-C(50) spacing. Because of the weak tube-C(50) interaction, the geometric and electronic structures of the peapods do not change greatly for the most stable configurations, but the selectivity in the interwall spacing and isomer encapsulation can be useful in separating various carbon fullerenes and their isomers.     

Low-lying isomers of the B9(-) boron cluster: the planar molecular wheel versus three-dimensional structures

The B(9)(-) cluster was found previously to be an unprecedented molecular wheel containing an octacoordinate planar boron with D(8h) symmetry in a combined photoelectron spectroscopy (PES) and theoretical study [H. J. Zhai et al., Angew. Chem., Int. Ed. 42, 6004 (2003)]. However, the PES spectra of B(9)(-) exhibit minor features that cannot be explained by the global minimum D(8h) structure, suggesting possible contributions from low-lying isomers at finite temperatures. Here we present Car-Parrinello molecular dynamics with simulated annealing simulations to fully explore the potential energy surface of B(9)(-) and search for low-lying isomers that may account for the minor PES features. We performed density functional theory (DFT) calculations with different exchange-correlation functionals and ab initio calculations at various levels of theory with different basis sets. Two three-dimensional low-lying isomers were found, both of C(s) symmetry, 6.29 (C(s)-2) and 10.23 (C(s)-1) kcal/mol higher in energy than the D(8h) structure at the highest CCSD(T) level of theory. Calculated detachment transitions from the C(s)-2 isomer are in excellent agreement with the minor features observed in the PES spectra of B(9)(-). The B(9)(-) cluster proves to be a challenge for most DFT methods and the calculated relative energies strongly depend on the exchange-correlation functionals, providing an excellent example for evaluating the accuracies of various DFT methods.