Solid-state NMR spectroscopy of molecular hydrogen trapped inside an open-cage fullerene

Solid-state 1H experiments were performed an open-cage fullerene hosting molecular hydrogen. The anisotropy of the molecular hydrogen rotation was studied by double-quantum magic-angle-spinning NMR. The time scale of the molecular hydrogen rotation was estimated by spin-lattice relaxation measurements as a function of temperature.     

The reaction of fullerene C(60) with 4,6-dimethyl-1,2,3-triazine: formation of an open-cage fullerene derivative.

A thermal reaction of fullerene C(60) with 4,6-dimethyl-1,2,3-triazine (4) in o-dichlorobenzene gave azacyclohexadiene-fused fullerene derivative 5, by the reaction with intermediate azete 11, and then, after flash chromatography over SiO(2), open-cage fullerene derivative 6 having an eight-membered ring orifice on the C(60) cage. Compound 6 is assumed to be formed via addition of diradical intermediate 13 to C(60). Compound 6 underwent a further photochemical reaction with singlet oxygen with the cleavage of one of the double bonds at the rim of the orifice to afford triketone derivative 8 having a 12-membered ring orifice.     

Theoretical investigation of an energetic fullerene derivative

A self‐consistent estimation method for the thermochemical properties of N‐methyl‐3‐(2′,4′,6′‐trinitrobenzene)‐fulleropyrrolidine (MTNBFP) is presented. This method is based on enthalpy of formation (Δ_fH) and enthalpy of combustion obtained from BLYP/DNP calculations of the total energies and frequencies for MTNBFP. The enthalpy of formation was calculated by an optimized set of isodesmic reactions given the available experimental Δ_fH of relative compounds. MTNBFP has a high enthalpy of formation, 2782.2 kJ/mol. Detonation velocity and detonation pressure were also presented in terms of Kamlet and Jacobs equations. Drop hammer impact sensitivity tests and blasting point per 5 s tests indicate MTNBFP may be a potential candidate primary explosive. To understand the test results well, we proposed a series of chemical reaction mechanisms and interpreted the relationship between impact sensitivity and electronic structures from the viewpoint of nitro group charge, electrostatic potential, and vibrational modes. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Spectrophotometric and thermodynamic studies of [60]fullerene/methylbenzene charge transfer complexes

The absorption spectra of charge-transfer (CT) complexes of [60]fullerene with liquid methylbenzenes, viz. toluene, o-xylene, m-xylene, p-xylene and mesitylene have been investigated in CCl(4) medium. An absorption band due to CT transition is observed in each case in the visible region. The experimental CT transition energies are well correlated (through Mulliken's equation) with the ionisation potentials (I(D)) of the series of methylbenzenes studied. From an analysis of this variation the electron affinity of [60]fullerene has been found to be 2.32 eV. The degrees of charge transfer in the ground state of the complexes have been found to be very low (0.66-0.775%). It has been found that these methylbenzenes form stable 1:1 complexes with [60]fullerene. Formation constants of the complexes have been determined at four different temperatures from which the enthalpies and entropies of formation of the complexes have been obtained. The experimentally determined formation constants of the complexes of [60]fullerene with methylbenzenes exhibit a very good linear free energy relationship (Chem. Rev. 53 (1953) 191).     

Pocket and antipocket conformations for the CH4@C84 endohedral fullerene

The endohedral fullerene CH₄@C₈₄ has been studied using density functional theory (DFT) and second‐order Møller–Plesset perturbation theory (MP2). In addition to the structure with a C? H bond of CH₄ in a tetrahedral pocket conformation, we find an alternative minimum, very close in energy (6.3–9.5 kJ/mol higher according to the level of theory), with the methane inverted, which we call the antipocket conformation. Computed IR spectra are reported for CH₄@C₈₄ and also for the reference system CH₄@C₆₀. The calculated vibrational levels, in a harmonic approximation, reveal close‐lying translational, librational, and shell‐vibrational modes. The results are also presented for the isoelectronic species NH@C₆₀. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Synthesis of 18-membered open-cage fullerenes through controlled stepwise fullerene skeleton bond cleavage processes and substituent-mediated tuning of the redox potential of open-cage fullerenes

Oxidation of the fullerenediol C(60)(OH)(2)(O)(OAc)(OOtBu)(3) with PhI(OAc)(2) yields the open-cage fullerene derivative C(60)(O)(2)(O)(OAc)(OOtBu)(3)2 with an 11-membered orifice. Compound 2 reacts with aniline to form a new open-cage derivative with a 14-membered orifice, which yields an 18-membered open-cage fullerene derivative upon addition of another molecule of aniline. Two different types of aniline derivatives with either electron-donating or electron-withdrawing substituents can be added sequentially, affording an unsymmetrical moiety in the open-cage structure. Reduction potentials of the 18-membered open-cage fullerene derivatives can be fine-tuned by changing the substituents on the aniline. The results provide new insights about the mechanism of open-cage reactions of fullerene-mixed peroxide.     

Theoretical studies on the smallest fullerene: from monomer to oligomers and solid States

Hybrid B3LYP and density-functional-based tight-binding (DFTB) computations on the solid-state structures and electronic properties of the C(20) fullerene monomer and oligomers are reported. C(20) cages with C(2), C(2h), C(i), D(3d), and D(2h) symmetries have similar energies and geometries. Release of the very high C(20) strain is, in theory, responsible for the ready oligomerization and the formation of different solid phases. Open [2+2] bonding is preferred both in the oligomers and in the infinite one-dimensional solids; the latter may exhibit metallic character. Two types of three-dimensional solids, the open [2+2] simple cubic and the body-centered cubic (bcc) forms, are proposed. The energy of the latter is lower due to the better oligomer bonding. The open [2+2] simple cubic solid should be a conductor, whereas the bcc solids are insulators. The most stable three-dimensional solid-state structure, an anisotropically compressed form of the bcc solid, has a HOMO-LUMO gap of approximately 2 eV and a larger binding energy than that of the proposed C(36) solid.     

100% encapsulation of a hydrogen molecule into an open-cage fullerene derivative and gas-phase generation of H2@C60

By applying high-pressure H2 to a new fullerene derivative, C63NO2SPh2Py (1), having a 13-membered-ring orifice, 100% incorporation of a H2 molecule into the fullerene cage has been achieved for the first time. This result substantiates the theoretical calculations indicating that the energy barrier required for H2 insertion through an orifice in 1 is considerably lower than that for the previously reported derivative with the largest orifice among open-cage fullerenes synthesized thus far. Upon matrix-assisted laser desorption/ionization mass spectroscopy, the removal of organic addends from the fullerene derivative 1 encapsulating H2 and restoration of the pristine C60 cage, which retains approximately one-third of incorporated H2, have been observed.     

反式共轭类碳烯CH2=CH-CH=C:LiF的构型及异构化反应

用MP2／6－31G^**解析梯度方法研究了反式共轭类碳烯CH2＝CH－CH＝C：LiF的结构。得到3个平衡构型和2个异构化反应的过渡态。计算结果表明，反式共轭类碳烯有两种比较稳定的平衡构型。分析了各平衡构型的结构特点及稳定性，给出了各种平衡构型及过渡态结构的Mulliken集居数，并讨论了两种稳定构型的化学活性。     

Theoretical studies of structures and stabilities of a new odd-numbered fullerene dimer: C141

The possible isomers of a newly synthesized C(141) molecule are calculated using MNDO, AM1, PM3, B3LYP/3-21G, and B3LYP/6-31G(d) methods. The geometry optimizations showed that the isomer 8-8 has the lowest total energy in all 64 possible structures of C(141). Unlike those of C(130), C(140), etc., the C(141) 8-8 shows a new structure: two C(70) side cages open [6.6] ring junctions located at the equator (instead of cap) area to create new chemical bonds for the bridge atom. Theoretical measurements of the average length of the long and short axes of C(70) side cages in the C(141) molecule reveal that when two C(70) cages are connected with each other at the equators, their geometric shapes become more spherical compared with the pristine C(70); this leads to a reduction of the molecular polarizability. Analysis of the local and global strain indicates that the global strain of C(70) monomer in the C(141) 8-8 is greatly reduced compared to the pristine C(70). The stable C(70) derivatives that are formed with reacted C-C bonds in the equator area may put new insights into fullerene chemistry, in particular, for C(70) to react with a large molecule. The results are discussed together with the experimental data.     

Theoretical studies on the reaction mechanism of CH2CH radical with HNCO

The reaction mechanism of CH₂CH radical with HNCO has been investigated systematically by density functional theory (DFT). The geometries and harmonic frequencies of reactants, intermediates, transition states, and products have been optimized with the B3LYP at different levels. At the same time, AIM is performed to calculate the charge density of some bonding critical points and the charges of some atoms. Nine feasible reaction pathways have been investigated. The results indicated that the main pathway is CH₂CH + HNCO → IMA1 → TSA1 → CH₂CH₂ + NCO, which is characterized by hydrogen atom transferring. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Fine tuning of the orifice size of an open-cage fullerene by placing selenium in the rim: insertion/release of molecular hydrogen

A newly synthesized open-cage fullerene containing selenium in the rim of the 13-membered-ring orifice allows milder conditions for hydrogen insertion, and the rate for hydrogen release is ca. three times faster than its sulfur analogue.     

Ab initio MO studies of nuclear spin-spin coupling constants in CH4, SiH4, AlH 4 − and GeH4 systems

Summary Ab initio molecular orbital calculations of electron coupled nuclear spin-spin coupling constants are performed for CH₄, SiH₄, AlH ₄ ^– and GeH₄ systems using the SCF perturbation theory. Basis set dependence of the major contributing terms such as orbital diamagnetic, orbital paramagnetic, spin dipolar and Fermi contact terms are studied. The study also illustrates the relative importance of bond centred functions and nuclear centred polarization functions in predicting the directly bonded and geminal couplings in the systems selected. Basis sets having uncontracted cores functions and augmented with bond functions seem to predict most of these couplings fairly satisfactorily when compared to the experimental values.     

Theoretical study of fullerene derivatives: C40H4 and C40X4 cluster molecules

Herein we demonstrate that the C₄₀ cluster molecule is easily formed to T_d symmetry structure and its ground state is ⁵A₂ open shell with four unpaired electrons. These four unpaired electrons are located at the tip points of the T_d symmetry structure. This work also indicates that these four unpaired electrons can easily react with a single valence atom, such as hydrogen or halogen atoms, to form a stable carbon hydrogen cluster molecule, C₄₀H₄, and carbon halogen cluster molecules, C₄₀X₄ (X=F, Cl, Br, I), respectively. The PM3 semiempirical molecular orbital method from Gaussian 94W computer program package was applied very well to these cluster molecules. According to the results in this study, the structures of geometrical optimization, ionization potential, energy gap, heat of formation, atomization energy, vibration frequency, and the remaining data of C₄₀H₄ and C₄₀X₄ cluster molecules. The above-calculated data prove that these unknown cluster molecules are stable and have a stable capacity similar to 1,3,5,7-tetrahaloadamantane molecules. They can be possibly synthesized experimentally in the near future. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 273–284, 1998     

Theoretical study of fullerene derivatives: C28H4 and C28X4 cluster molecules

Based on the basic theory of C₂₈ cluster molecule proven by H. W. Kroto and the research findings of C₂₈'s derivative such as Ti@C₂₈* and Mg@C₂₈, proven by T. Guo, B. I. Dunlap, O. D. Haberlen, and others, we examine the two series fullerene derivatives, C₂₈H₄ and C₂₈X₄ cluster molecules, which are formed by the skeleton of C₂₈ cluster molecule. In this work, we not only prove that C₂₈ cluster molecule belongs to the T_d symmetry structure and its ground state is ⁵A₂ open-shell with four unpaired electrons, but also find that C₂₈ can easily react with single valence electron atoms, like hydrogen atom and halogen atoms, to be formed to stable fullerene derivatives, C₂₈H₄ and C₂₈X₄ cluster molecules (X=F, Cl, Br, I). The PM3 semiempirical molecular orbital method from G94W and Hyperchem program packages were applied very well in these fullerene derivatives. According to the results presented herein, we obtain the structures of geometrical optimization, ionization potential energy gap, heat of formation, atomization energy, and vibration frequency data of the C₂₈H₄ and C₂₈X₄ cluster molecules. The above calculation data confirm that these unknown fullerene derivatives are stable molecules; the stable behavior resembles the 1,3,5,7-tetrahaloadamantane molecules. It is quite possible that they can be synthesized experimentally in the near future. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 187–197, 1998     

多溴代芴热力学性质的理论预测研究

为了预测环境污染物多溴代芴的热力学性质,计算了60种多溴代芴的分子连接性指数、电性距离矢量指数、电性拓扑状态指数以及分子形状指数.采用多元线性回归的方法建立了多溴代芴化合物的标准生成焓(Δ_fH~0)、标准熵(S~0)、标准生成吉布斯自由能(Δ_fG~0)及等容热容等热力学性质的QSPR相关性模型,方程的相关系数值均在0.99以上.与相关文献的相关系数R和标准误差S进行比较,该模型具有良好的预测能力和稳定性.     

The outside knows the difference inside: trapping helium by immediate reduction of the orifice size of an open-cage fullerene and the effect of encapsulated helium and hydrogen upon the NMR of a proton directly attached to the outside

A methodology to entrap He inside an open-cage fullerene by immediate reduction of the size of an orifice was developed, and the effects of encapsulated He and H(2) on the chemical shift of a proton directly attached to the outer fullerene sphere were revealed.