He+C60↔(He@C60)的反应势垒研究

The reaction barriers of (He+C60(He＠60)) have been calculated by the quantum-chemical method EHMO/ASED in the following four paths: (1) penetrate through the pentagon on the C60 cage; (2) penetrate through the hexagon on the C60 cage,(3) penetrate through the short bond; (4) penetrate through the long bond. Corresponding to each path, there are two choices: (a) while He penetrate C60 cage, the distances of the C’s which are the most adjacent to He are changed with a planar extension and a concerned window is formed; (b) while He penetrate C60 cage, the distances of the C’s which are the most adjacent to He are changed with a spherical extension and a concerned window is formed. The results are given in Figs. 1-2 and Tables 1-2. It is shown that the reaction through path(4) with choice (a) has the least reaction barrier, being optimum. At that case, a window of 9-membered ring is formed. Because the window extension of C6H6 is more free than that of C60, the barrier of He penetrating through C6H6 will be lower than that of He penetrating through C60.     

Do Carbon Nano-onions Behave as Nanoscopic Faraday Cages? A Comparison of the Reactivity of C60, C240, C60@C240, Li+@C60, Li+@C240, and Li+@C60@C240

From the analysis of the polarizability of carbon nano-onions (CNOs), it was concluded that CNOs behave as near perfect nanoscopic Faraday cages. If CNOs behave as ideal Faraday cages, the reactivity of the C₂₄₀ cage should be the same in Li⁺@C₂₄₀ and Li⁺@C₆₀@C₂₄₀. In this work, the Diels–Alder reaction of cyclopentadiene to the free C₂₄₀ cage and the C₆₀@C₂₄₀ CNO together with their Li⁺-doped counterparts were analyzed using DFT. It was found that in all cases the preferred cycloaddition is on bond [6,6] of type B of C₂₄₀. Encapsulation of Li⁺ results in lower enthalpy barriers due to the decrease of the energy of the LUMO orbital of the C₂₄₀ cage. When the Li⁺ is placed inside the CNO C₆₀@C₂₄₀, the decrease in enthalpy barrier is similar to that of Li⁺@C₂₄₀. However, the location of Li⁺ in Li⁺@C₂₄₀ (off-centered) and Li⁺@C₆₀@C₂₄₀ (centered) is quite different. When Li⁺ was placed in the center of the C₂₄₀ cage in Li⁺@C₂₄₀, the barriers increased significantly. Taking into account this effect, the barriers in Li⁺@C₂₄₀ and Li⁺@C₆₀@C₂₄₀ differ by about 4 kcal mol⁻¹. This result can be attributed to the shielding effect of C₆₀ in Li⁺@C₆₀@C₂₄₀. As a result, we conclude that this CNO does not act as a perfect Faraday cage.     

Electronic structure and the hydrogen-shift isomerization of hydrogen nitryl HNO2

Summary Electronic structure of hydrogen nitryl HNO₂, a yet not identified entity, and the path of its possible isomerization totrans-HONO have been investigated byab initio SCF and MRD-CI computations using the 6-31G** basis set. HNO₂ isC _2v -symmetric and its ground state (¹ A ₁) is less stable thantrans-HONO by 66 kJ/mol (with the SCF vibrational zero-point energy correction). The lowest two excited singlet states (¹ A ₂ and¹ B ₁) are nearly degenerate, their vertical excitation energies being predicted to be 4.8 eV. The isomerization path is traced by the CASSCF procedure and the activation barrier height is evaluated by the CI treatment. HNO₂ in its ground state isomerizes totrans-HONO by maintaining the planar (C _s-symmetric) structure. The activation energy is calculated to be 171 kJ/mol, which is clearly lower than the calculated H-N bond energy (253 kJ/mol). The transition state seems to be more adequately described as an interacting system of proton and the nitrite anion rather than as a pair of two fragment radicals.     

Exohedral functionalization of C60 by [4+2] cycloaddition of multiple anthracenes

By using density functional theory, we have investigated [4+2] cycloaddition of one to four anthracene (ANT) molecules to a C₆₀ fullerene which has been already studied by experimentalists. It was found that the reaction is regioselective and the ANT molecule prefers to be adsorbed atop a C–C bond of the C₆₀ which is shared between two hexagons with reaction energy of ?25.2 kcal/mol (for one ANT). The HOMO of the ANT interacts with the LUMO of the C₆₀ via a cycloaddition reaction. Also five regioisomeric bis-adducts of ANT/C₆₀ complexes were compared from stand point of stability. Increasing the number of attached ANTs, the reaction energy becomes less negative. The HOMO–LUMO energy gap of C₆₀ is slightly changed and the potential barrier of the field electron emission from its surface may be reduced upon the reaction.     

Pd/Cu(111)双金属表面催化糠醛脱碳及加氢的反应机理

采用密度泛函理论(DFT)研究糠醛在最稳定Pd/Cu(111)双金属表面上的吸附构型和糠醛脱碳及加氢的反应机理。结果表明,当糠醛初始吸附于O_3-Pd-top、O_7-Cu-hcp位时,吸附构型最稳定,其吸附能为73.4 kJ/mol。糠醛在Pd/Cu(111)双金属表面上更易发生脱碳反应。对于糠醛脱碳反应,所需活化能较低,各个基元反应均为放热反应,糠醛更易先失去支链上的H形成(C_4H_3O)CO,然后中间体脱碳加氢得到呋喃,其中,C_4H_3O加氢生成呋喃所需活化能(72.6 kJ/mol)最高,是反应的控速步骤。对于加氢反应,糠醛与首个氢原子的反应需要最大的活化能(290.4 kJ/mol),是反应的限速步骤。     

Thermochemistry of Solvated Crystals of C60> and C70> with o-Xylene

Differential scanning calorimetry (DSC) was used to study the binary systems of C₆₀-o-xylene and C₇₀-o-xylene and the ternary system C₆₀-C₇₀-o-xylene. Fullerene C₆₀ formed solvated crystals C₆₀·2C₈H₁₀ with incongruent melting point 320 K and with enthalpy of decomposition 31±3 kJ (mol of C₆₀)^-1. Two solvated crystals of C₇₀ with incongruent melting points 283 and 369 K, and with decomposition enthalpies 18.5±2.2 and 23.0±1.5 kJ (mol of C₇₀)^-1, were formed from o-xylene solutions. Three ternary compositions with C₆₀/C₇₀ mole ratios of 3:1, 1:1 and 1:3 were scanned by DSC. This revised version was published online in July 2006 with corrections to the Cover Date.     

Standard enthalpy of formation of fullerene bromide C60Br24

The enthalpy of the combustion of C₆₀Br₂₄ · 2Br₂ has been measured using a rotating-bomb calorimeter as follows: Δ _c H ⁰(C₆₀Br₂₄ · 2Br₂, cr) = (?25986 ± 166) kJ/mol. The result has been used to calculate the standard enthalpy of formation, ΔfH ⁰(C₆₀Br₂₄ · 2Br₂, cr) = (2375 ± 166) kJ/mol. The enthalpies of formation of C₆₀Br₂₄ (cr) and dissociation of the C-Br bond have been estimated. The latter value has been compared with enthalpies for the C-X (X = H, F, Cl, Br) bonds in fullerene derivatives and organic compounds.     

The standard enthalpy of formation of fullerene chloride C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>

A rotating-bomb calorimeter was used to measure the energy of combustion of crystalline fullerene chloride C₆₀Cl₃₀ · 0.09Cl₂, Δ_c U° = (?24474 ± 135 kJ/mol). The result was used to calculate the standard enthalpy of formation, Δ_f H° (C₆₀Cl₃₀, cr) = 135 ± 135 kJ/mol, and the C-Cl bond energy, 195 ± 5 kJ/mol. The C-X (X = F, F, Cl, and Br) bond energies in fullerene C₆₀ derivatives and other organic compounds are compared.     

Theoretical investigation on icosahedral C60(FeCp)12: A hybrid of C60 and ferrocene

A perfect hybrid complex C₆₀(FeCp)₁₂ is predicted using density functional theory method_. This fullerene derivative could be view as a C₆₀ cage of which each C₅ ring coordinates a (FeCp) ligand. Theoretical calculation reveals that it has a large lowest unoccupied molecular orbital–highest unoccupied molecular orbital gap (2.53 eV) and keeps the I_h symmetry of C₆₀. But the C? C bond length of its inner C₆₀ cage trends to be uniform, which is quite different from the bonding character of C₆₀ fullerene. Further investigation reveals that the chemical bonding, TDOS and the aromaticity of the (C₅FeCp) unit in C₆₀(FeCp)₁₂ are similar as those of ferrocene molecule, which indicates the similarity of their electronic properties. So, this compound could be viewed as the combination of ferrocene molecules. Thus, its unconventional formation process from 12 Fe(Cp)₂ is proposed and the reaction energy is calculated. As the C₆₀(FeCp)₁₂ compound has the geometry framework as C₆₀ and the electronic characters as ferrocene, it would inherit the outstanding properties from both two molecules and have wild potential applications in nanochemistry. We hope our study could give some references for the further investigation and experimental synthesis research of the C₆₀(FeCp)₁₂ compound. © 2015 Wiley Periodicals, Inc.     

Investigation on the interaction on and the rotation of C60 in alkali-doped complexes AXA′3-XC60 (X = 1, 2, 3; A,A′ = alkali)

The interaction on and the rotation of C₆₀ in akali-doped C₆₀ solids, A_XA′_3-XC₆₀ (X = 1, 2, 3; A, A′ = alkali), have been calculated with Buckingham potential model. The results show that the total interaction on C₆₀ changes dramatically when the pure C₆₀ solid is alkali-doped into K₃C₆₀. The interaction on C₆₀ in K₃C₆₀ is about 20 times greater than that in pure C₆₀. And the main component in the former, occupying > 90% is electrostatic, while in the latter, the main components, occupying > 90%, are dispersive and repulsive. The results also show that in contrast to the whole-region free rapid rotation of C₆₀ molecule in its pure solid, the rotation of C₆₀ in K₃C₆₀ is mostly forbidden due to a 10 times increase (reaching about 300 kJ/mol) in potential barrier, except for the region from 0° to 50° where a broad, smooth, and shallow potential well exists. Calculations for alkali-doped complexes other than K₃C₆₀, i.e., A_XA′_3-XC₆₀ (X = 1, 2, 3; A, A′ = K, Rb, Cs), come to the same conclusion. Finally, an interesting and meaningful result is that the superconducting transition temperatures of A_XA′_3-XC₆₀ (X = 1, 2, 3; A, A′ = K, Rb, Cs) change inversely with the total interactions on C₆₀. © 1995 John Wiley & Sons, Inc.     

NMR Properties of Polylithiated C60

Endohedral, ¹³C, ⁷Li, and nucleus‐independent (NICS) chemical shifts are reported for selected Li_nC₆₀ isomers (n = 6, 12, 18) at the GIAO (gauge‐including atomic orbitals)‐SCF/DZP//BP86/3–21G level. Li₆C₆₀ closely resembles C₆₀^6– in terms of NMR criteria for aromaticity, as evidenced by an exceptionally high endohedral shielding. In contrast, nonaromaticity is indicated for Li₁₂C₆₀, based on a positive endohedral chemical shift. NICS and δ(endo) values very similar to those of Li₁₂C₆₀ are obtained for Li₁₈C₆₀. According to population analysis, indeed the same number of electrons are transferred to the fullerene cage in both cases. Endohedral chemical shifts, accessible via ³He NMR of the corresponding endohedral helium compounds, could thus be a valuable indicator for the extent of reduction of the C₆₀ molecule. Energetic estimates suggest that in the bulk, Li₁₂C₆₀ should be unstable with respect to decomposition into Li₆C₆₀ and lithium metal.     

A covalent organic cage compound acting as a supramolecular shadow mask for the regioselective functionalization of C60

A trigonal-bipyramidal covalent organic cage compound serves as an efficient host to form stable 1 : 1-complexes with C₆₀ and C₇₀. Fullerene encapsulation has been comprehensively studied by NMR and UV/Vis spectroscopy, mass spectrometry as well as single-crystal X-ray diffraction. Exohedral functionalization of encapsulated C₆₀via threefold Prato reaction revealed high selectivity for the symmetry-matched all-trans-3 addition pattern.

The taming of the Prato reaction: a covalent organic cage compound serves as a supramolecular template for the regioselective functionalization of C₆₀.     

A New Approach to C60-Containing Polyphosphazenes by Polymerization of Phosphonitrile Chloride Trimer in the Presence of C60

A novel synthetic strategy was developed to prepare polyphosphazenes containing C60 moieties. Thus, the phosphonitrile chloride trimer underwent thermal ring-opening polymerization （ROP） in the presence of C60 molecules to yield the reactive macromolecular intermediate, C60-containing poly（dichlorophosphazene）. And then, the other groups could be linked to the phosphazene backbone by nucleophilic substitution reaction of the chlorine atoms in this intermediate to produce a series of C60-containing polyphosphazene. The polymer exhibits good solubility in common organic solvents and is thermally stable.     

Theoretical studies of cyclopropylsilylenes: The structures and stability of cyclopropylsilylene C3H5SiH

Ab initio molecular orbital calculations at the G2(MP2) level have been carried out on cyclopropylsilylene C₃H₅SiH. Four equilibrium structures were located. Like H₂Si, the ground state of C₃H₅SiH is singlet and the triplet is the low‐lying excited state. The singlet–triplet separation energy is 127.9 kJ/mol. The cis‐trans isomerization path of singlet cyclopropylsilylene was investigated by intrinsic reaction coordinate (IRC) calculations. The calculations show that no gauche conformers exist along the potential energy curve of the cis‐trans isomerization and the isomerization happens with a barrier of 30.1 kJ/mol. Changes (ΔH and ΔG) in thermodynamic functions, equilibrium constant K(T), and A factor and reaction rate constant k(T) in Eyring transition state theory of the cis‐trans isomerization were also calculated. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Energy relationship and the polarization of C_(60) cage in the endohedral complexes (X@C_(60))

In this paper, we carry out the calculation on the system (X@C60)(X=Li, Na, K, Kb, Cs; F, Cl, Br, I), where the position of X changes along 5 typical symmetry directions. For the calculation of quantum chemistry we use EHMO/ASED method, for the calculation of molecular mechanics we use Buckingham potential (exp-6-1) function, and for the calculation of thermo-chemical cycle we use individually isolating the processes such as the structure variation, charge transfer and charge distribution, and their interactions etc. The calculation results show that (1) In the region of radius r≈0.2 nm of the Ceo cage, the potential field is nearly spherical; (2) Except for Li and Na, the systems are the most stable with minimum energies at the center of C60 cage. For Li and Na, the systems are the most stable with minimum energies at r≈0.16 nm and r≈0.13 nm, respectively. In view of the interactive region of chemical bonds, the interactions between X and the C60 cage do not belong to the classical chemical bonds; (     

Thermal stability of the fullerene‐chain link in 6‐arm PS stars with a C60 core

The thermal stability of well‐defined hexa‐adducts (PS)₆C₆₀ in solution at temperatures around 100 °C has been studied by multi‐detector Size Exclusion Chromatography. The degradation reaction corresponds to a quantitative release of the polystyrene arms from the fullerene core through thermal cleavage of the PS‐C₆₀ link. From the kinetics of formation of cut arms and the progressive decrease of the stars' functionality, we could establish that the reaction follows a stepwise “breaking” mechanism where a 6‐arm star is first converted to a 5‐arm star, then to a 4‐arm star, and so on down to the ungrafted arm. Furthermore, not only does the thermal stability of the PS? C₆₀ bond increase if the functionality of the star decreases, but the difference is large enough to allow determination of the kinetics constants for the first three steps. The activation energy for the breaking of an arm‐C₆₀ link is about 65 kJ/mol. The stability of (PS)₆C₆₀ slightly decreases with an increase of the arm length. MALDI‐TOF mass spectroscopy has shown that both C? C bonds in α and β positions to C₆₀ can be cut, but the breaking of the direct fullerene‐arm bond is favored. We have also found that a polyisoprene? C₆₀ bond is about seven times less stable than a PS‐fullerene link upon heating. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4820–4829, 2004     

Endohedral Complex of Fullerene C<Subscript>60</Subscript> with Tetrahedral N<Subscript>4</Subscript>, N<Subscript>4</Subscript>@C<Subscript>60</Subscript>

B3LYP/6-31G(d) hybrid HF/DFT and BLYP/6-31G(d, p) DFT calculations were carried out to determine the structural and electronic properties of the endohedral complex of C₆₀ with Tetrahedral N₄ (T_d N₄), N₄@C₆₀. It was demonstrated that N₄ was seated in the center of the fullerene cage and the tetrahedral structure of N₄ is remained in the cage. The formation of this complex is endothermic with inclusion energy of 37.92 kcal/mol. N₄ endohedral doping perturbs the molecular orbitals of C₆₀ not so much, the calculated HOMO–LUMO gaps, the electron affinity (EA) and the ionizational potential (IP) of N₄@C₆₀ are similar to that of C₆₀.     

Concise Synthesis of Open‐Cage Fullerenes for Oxygen Delivery

Open‐cage fullerenes with a 19‐membered orifice were prepared in three steps from C₆₀. The key step for cage‐opening is aniline mediated ring expansion of a fullerene‐mixed peroxide with a ketolactone moiety on the orifice. Release of ring strain on the spherical fullerene cage served as the main driving force for the efficient cage‐opening sequence. Encapsulation of oxygen could be achieved at room temperature under moderate pressure (50 atm) and the encapsulated oxygen could be released slowly under ambient conditions. The activation energy of the oxygen‐releasing process is 18.8 kcal mol^?1 and the half‐life at 37 °C was 73 min, which makes this open‐cage fullerene derivative a potential oxygen‐delivery material.     

A computational study of the endohedral fullerene GeH4@C60

The structures, stabilities, and electronic properties of the endohedral fullerene GeH₄@C₆₀ have been systematically studied by using the hybrid DFT-B3PW91 functional in conjunction with 6-31G(d) basis sets. Our calculated results show that the GeH₄ molecule is more compact in the center of the C₆₀ cage and exists in molecular form inside the fullerene. The Zero-Point and BSSE corrected binding energy of GeH₄@C₆₀ is −1.77 eV. The calculated HOMO–LUMO energy gap, the vertical ionization potentials (VIP) and vertical electron affinities (VEA) are similar to that of C₆₀ cage. It is indicated that GeH₄@C₆₀ also seems to be very stable species. Natural population analysis on the GeH₄@C₆₀ reveals that the central GeH₄ only gain −0.06 charges from the C₆₀ cage. Additionally, the vibrational frequencies and active infrared intensities of GeH₄@C₆₀ are also discussed.     

The mechanism of the retro-Diels-Alder reaction in 4-vinylcyclohexene cation radical

Butadiene cation radicals are produced symmetrically from the ring and side-chain of the vinylcyclohexene cation radical near the onset of the fragmentation. The appearance energies of C₄H₆^+? and C₄H₂D₄^+? from (3,3,6,6-D₄)vinylcyclohex ene were measured as 11.07 ± 0.05 and 11.06 ± 0.06 eV, respectively. This sets the barrier to retro-Diels-Alder decomposition at 1140 kJ mol^?1 above the energy of 1 and 44 kJ mol^?1 above the thermochemical threshold corresponding to C₄H₆^+? + C₄H₆. Topological molecular orbital calculations indicate that this lowest-energy path involves a sequential rupture of the C₃C₄ and C₅C₆ bonds, with a calculated barrier of 211 kJ mol^?1. The second, two-step reaction channel proceeds by subsequent fission of the C₅C₆ and C₃C₄ bonds with a barrier of 299 kJ mol^?1. This channel is found experimentally as a break on the ionization efficiency curve at 12.1 eV. Both the supra-supra and the supra-antara pericyclic reactions go through energy maxima and are therefore forbidden. The supra-supra process is the most favorable route for decomposition from the first excited state, the activation energy being 333 kJ mol^?1. The preference for the two-step mechanism is due to hyperconjugative stabilization of intermediate molecular configurations.