Calculations of the water-dimer encapsulations into C84

The water-dimer formation and its encapsulation into D₂(22)-C₈₄ and D_2d(23)-C₈₄ fullerenes is evaluated. The water-dimer populations are computed using the potential-energy change from the G3 theory and anharmonic partition functions from the MP2/AUG-cc-pVQZ approach. The encapsulation energetics is treated at the M06-2X/6-31++G** level and it is found that the water-dimer storage in C₈₄ is attractive, yielding an energy gain of more than 10 kcal mol^?1. This substantial encapsulation energy together with the computed temperature increase of the water-dimer population in the saturated steam suggests that the (H₂O)₂@C₈₄ endohedrals could be produced in a high-temperature/high-pressure approach similarly to encapsulation of rare gases in fullerenes.     

B3LYP/6-31G∗//SAM1 Calculations of C36 Fullerene and quasi-Fullerene Cages

Abstract

The recently isolated fullerene C₃₆ is computed by the SAM1 method with energetics refined at the B3LYP/6-31G? level. Twelve low-energy cages are considered in detail, exhibiting both fullerene (pentagons and hexagons) and quasi-fullerene (also squares and heptagons) pattern. In contrast to other fullerene systems, the SAM1 and B3LYP/6-31G? methods do produce somewhat different energetics. Consequently, the equilibrium isomeric composition at high temperatures is different, too. In the best affordable B3LYP/6-31G? approach the fullerene cage with the topological D _6d symmetry represents the most populated species at high temperatures. Hence, an agreement with the solid-state NMR experiment is achieved at the B3LYP/6-31G? theoretical level.     

Singlet‐Triplet Transition in the C60 2− Dianion

Abstract

The C₆₀ complexes with decamethylcobaltocene: (Cp*₂Co)₂C₆₀(C₆H₄Cl₂, C₆H₅CN)₂ (1) and [K · (18‐crown‐6)]₂ · C₆₀ · (DMF)₄ (2) have been obtained as single crystals by the diffusion method. The IR‐ and UV‐VIS‐NIR‐spectra justify the formation of the C₆₀ ^2? dianions in these salts. EPR measurements show that the low temperature signals of 1 in the 4–140 K range and 2 in the 4–60 K range have intensity corresponding only to 0.4% and 3.5% from total C₆₀. Because of this, most of the complexes are EPR silent, and, consequently, C₆₀ ^2? has a diamagnetic singlet (S = 0) state in these temperature ranges. The appearance of a broad EPR signal in the spectum of 1 above 140 K and 2 above ～60 K is assigned to a thermal population of a close lying excited triplet (S = 1) state. The singlet–triplet energy gap for C₆₀ ^2? in solid 1 and 2 was estimated to be 730 ± 10 and 300 ± 10 cm^?1.     

Cyclic and Linear Structures of C13: A Computational Study

Abstract

Recently, a linear structure of C₁₃ was observed and its infrared spectrum recorded. Computations of the linear and cyclic structures of C₁₃ are thus presented. The computations are performed at ab initio level using the standard 6-31G? basis set. Electron correlation is treated by density functional theory (Becke3LYP) and perturbation treatment (MP2=FC). With the density-functional approach the standard 6-311G? and 6-311G(2d,p) basis sets are applied, too. In all the treatments the cyclic structure (C _2v symmetry) is located about 90 kJ/mol below the linear form (D _∞h symmetry), while a tricyclic structure is considerably higher in energy (about 280 kJ/mol above the monocyclic species). Even at high temperatures the linear form represents less than 10% of the equilibrium isomeric mixture. Computed IR spectra are also reported. The stability evaluation corresponds to the findings of ion chromatography.     

金刚烷衍生物的晶体密度预测方法筛选

金刚烷类化合物稳定性高、密度大，是高能量密度化合物（HEDC）的理想目标物。采用密度泛函理论（B3LYP、M06-2X和B3PW91）结合5种基组（6-31G、6-31G*、6-31G**、6-311G*和6-31+G**），对15种已知实验密度ρ_e的金刚烷类化合物进行研究，以探寻适用于预测新型金刚烷类化合物晶体密度的方法。通过Monte-Carlo统计方法求得分子平均摩尔体积V，得到理论密度ρ_c，并与ρ_e相比较发现:3种密度泛函理论方法结合5种基组的平均绝对偏差均较小（0.04～0.07 g/cm³）;且ρ_c与ρ_e存在良好的线性关系,相关系数均大于0.98，标准偏差均小于0.05。建议使用M06-2X/6-31G*方法快速、准确地预测金刚烷类化合物的晶体密度。     

Computations of Low-Energy Non-Icosahedral Structures of C6− 60

Abstract

Owing to the three-fold degeneracy of the LUMO in C₆₀, its hexa-anion is not subjected to Jahn-Teller distortions. In contrast to the accepted presumptions, however, computations at the MNDO, AMI, PM3, SAM1, HF/STO-3G, HF/3-21G, and HF/4-31G levels show that the completely relaxed, non-icosahedral cage of C^6? ₆₀is lower in energy. The computed energy gain varies between 60 and 150 kJ/mol and thus, it is consistently significant (the most sophisticated approach, HF/4-31G, yields 93 kJ/mol). The longest C-C bond in the relaxed structures is at most computed 0.05 Å longer compared to the 5/6 bond in the icosahedral C^6? ₆₀The symmetry of C^6? ₆₀is relaxed to D₂ A C_2v, isomer is discussed, too.     

Molecular Complex of [60]Fullerene with 2-(4-thione-l,3-dithiolan-5-yliden)-4,5-dimethyl-1,3-diselenol [C60·2(DTDS)]: Synthesis,Crystal Structure and Properties

Abstract

New molecular complexes of [60]fullerene with 2-(4-thione-l,3-dithiolan-5-yliden)-4,5-dimethyl-l,3-diselenol [C₆₀·2(DTDS)] have been synthesized, crystal structure, IR spectral and electrochemical properties have been studied. Partial charge transfer has been found. An unusual shortening of the endocyclic S-C(sp²) bond in the DTDS molecule has been found to be stipulated by conformational vibrations of the >CH₂ group. A comparative analysis of the X-ray data for the [C₆₀·2(DTDS)] crystals and the quantum chemical calculations (SCF MO, 6-31G? basis) for the DTDS molecules and its radical ions showed charge transfer not to be the cause for the shortening of the exocyclic C=S bonds.     

Thermodynamic Properties of Bromomethanes and Bromomethyl Radicals: An ab Initio Study

Thermochemical data on volatile organic compounds containing bromine are needed for atmospheric modeling, in view of their ozone depletion potential upon photodissociation and the release of atomic bromine. Yet even for the bromomethane series, with the exception of CH₃Br, thermodynamic properties are not well established. Similarly, structural and thermochemical information on brominated methyl radicals is incomplete or not available. In this paper we have adopted a computational approach to obtain this needed information. Equilibrium geometries for the molecules CH_4–n Br _n (n = 0–4) and radicals CH_3–m Br _m (m = 0–3) were optimized at both HF/6-31G* and MP2/6-31G* levels of theory. Moments of inertia, harmonic vibrational frequencies, and thermodynamic functions were determined at the HF/6-31G* level. Electron correlation contributions were performed by single-point calculations at both second- and fourth-order Møller–Plesset perturbation theory for derived MP2/6-31G*geometries. Enthalpies of formation were obtained from a consideration of applicable isodesmic reactions using the derived MP4/6-31G**//MP2/6-31G* total energies in conjunction with experimentally established enthalpies of formation for CH₃Br, CH₄, and CH₃. These data were then used in the determination of and K _{f, T} for all species over the temperature range 0 to 1500K. A comparison was made to the existing standard enthalpies of formation at 298 K, both experimentally measured and theoretically estimated, for CH₂Br₂, CHBr₃, CBr₄, CH₂Br, CHBr₂, and CBr₃.     

Bromination of [60]Fullerene. II. Crystal and Molecular Structure of [60]Fullerene Bromides,C60Br6, C60Br8, and C60Br24

Abstract

The crystal and molecular structures of the bromofullerene solvates C₆₀Br₆·0.5C₆H₅Cl·0.5Br₂, C₆₀Br₈·1.5(o‐C₆H₄Cl₂), C₆₀Br₈·Br₂, C₆₀Br₈·0.5C₆H₅Br·0.5Br₂, and C₆₀Br₂₄·2Br₂ have been determined by single crystal X‐ray diffraction. The molecular species C₆₀Br₆, C₆₀Br₈, and C₆₀Br₂₄ which have idealized C _s , C _2v  , and T _h symmetries, respectively, have several different types of C?Br and C?C bonds. A comparison between different solvates of the same bromofullerenes revealed a larger stability of the packing modes for the C₆₀Br₆ and C₆₀Br₂₄ solvates, whereas the C₆₀Br₈ solvates showed different packing motifs dependent on the nature and amount of the solvent molecules.     

A Computational Treatment of 35 IPR Isomers of C88

Abstract

The complete sets of 35 isolated-pentagon-rule (IPR) isomers of C₈₈ is described by the SAM1 (Semi-Ab-initio Model 1) quantum-chemical method. The separation energetics is also computed at the HF/STO-3G, HF/3-21G, and HF/4-31G levels. The SAM1 and HF/4-31G data mostly agree within a few kJ/mol. As the SAM1 energetics does not reproduce the recent NMR observations, entropy contributions are included, too, being based on the harmonic-oscillator and rigid-rotator model. Considerable temperature effects on the relative stabilities in the system are found. The ground-state structure of C₈₈ is a C ₃ isomer, however, with an increase of temperature a C ₂ structure becomes important. At still higher temperatures a near C ₂ species is dominant. The results can be viewed as a good agreement with the available observations, and they further expand the family of the IPR sets where the thermodynamic equilibrium treatment allows for a satisfactory support of observations.     

MOLECULAR AND CRYSTAL STRUCTURE OF THE ADDUCTS OF C60F18 WITH AROMATIC HYDROCARBONS

ABSTRACT

The solubility of C₆₀F₁₈ in aromatic hydrocarbons, benzene, toluene, and xylenes (0.48–1.23?mg/mL), and decomposition enthalpies for the 1?:?1 and 1?:?2 complexes (31–70?kJ/mole) have been determined. The C₆₀F₁₈ molecule has near perfect C_3v symmetry, and the x-ray single-crystal structures of the C₆₀F₁₈?L complexes (L=hexamethylbenzene, o-, m-, p-xylene, and bromobenzene) are compared in terms of 12 types of C?C and four types of C–F bonds. Analysis of the packing modes in the crystals shows an influence of the size and polarity of the aromatic hydrocarbon molecule.     

New Polymeric Phase in Low‐Doped Lithium Intercalated Fullerides

Abstract

The low‐doped Li _x C₆₀ compounds (x≤6) were investigated using laboratory X‐ray and synchrotron radiation diffraction, ¹³C NMR and Raman spectroscopy. Li₄C₆₀ shows an unusual 2D polymerisation in which the C₆₀ units are connected both by [2+2] cycloaddition and by single carbon–carbon bonds, a unique feature among the known polymerised fullerene compounds. This picture is fully supported also by static NMR and Raman measurements. The charge transfer to C₆₀ in the polymeric phase was evaluated from the shift of the A_g(2) mode. The depolymerisation process was investigated as well; despite the presence of two different bonds, the polymer‐to‐monomer transition induced by thermal treatments is a single‐step phenomenon.     

Trifluoromethylated [60]Fullerenes: Synthesis and Characterization

Abstract

The high temperature reaction of C₆₀ with silver(I) trifluoroacetate followed by 500°C sublimation and HPLC purification has led to the characterization of the trifluoromethyl‐[60]fullerenes 1,4‐C₆₀(CF₃)₂, C _s‐C₆₀(CF₃)₄, C ₁‐C₆₀(CF₃)₄, and C ₁‐C₆₀(CF₃)₆ by EI‐MS and ¹⁹F NMR. The compounds C ₁‐C₆₀(CF₃)₄ and C ₁‐C₆₀(CF₃)₆ were obtained with 90+% compositional purity. A sample of C₆₀(CF₃)₂ also contained ca. 15–20% of a C _s‐symmetry isomer of C₆₀(CF₃)₄. The structural assignments are based on calculations at the AM1 and DFT levels of theory.     

Molecular structures of the open-shell IPR isomers of fullerene C90

Fifteen open-shell isomers off the forty six IPR isomers of fullerene C₉₀ were found and investigated: 5 (C_s), 7 (C₁), 9 (C₁), 10 (C_s), 11 (C₁), 20 (C₁), 21 (C₁), 22 (C₁), 23 (C₂), 24 (C₁), 25 (C_2v), 41 (C₂), 42 (C₂), 43 (C₂), and 44 (C₂). According to developed by us approach the positions of single, double, and delocalized π-bonds in the molecules of these isomers are shown for the first time. The obtained results of electronic and geometrical structures are fully supported by DFT method with the B3LYP functional at the 6-31G and 6-31G* levels. Molecules of these open-shell isomers contain different radical substructures (mainly the phenalenyl-radical substructures), they should be unstable and could not be obtained as empty molecules. Nevertheless, there is a possibility of obtaining them in polymeric forms or as endohedral or exohedral derivatives.     

Phase transformations in Fe–Ni–Cr heat-resistant alloys for reformer tube applications

Fe–35Ni–25Cr–0.4C alloys with different compositions are aged between 750 and 1150°C up to ～10,000?h. As-cast microstructure contains interdendritic carbides of type M₇C₃ (‘Cr₇C₃’) and MC (‘NbC’). At service temperatures, M₇C₃ transform into M₂₃C₆ (‘Cr₂₃C₆’) within hours. Then, a hardening precipitation of secondary intragranular M₂₃C₆ occurs over hundreds of hours, the nose of the ‘temperature-time-hardening’ curve being around 1000°C. G phase forms after long aging; its solvus temperature and formation kinetics depend on silicon content. Z phase is observed after long aging at 950°C or above. G and Z phases form at the expense of MC. Very long aging causes nitridation under air, with first a transformation of M₂₃C₆ into chromium-rich M₂X carbonitrides (X?=?C,N), then of MC into chromium-rich MX carbonitrides.     

Ab Initio Quantum Chemical Methods for Investigations of Fullerene C60, CS2 and Tetrathiafulvalene Molecules and Their Complexes

Abstract

Geometry and energy of formation of single molecules: fullerene C₆₀, CS₂ and tetrathiofulvalene (TTF) and their complexes: C₆₀ +CS₂ and C₆₀ +TTF were obtained using Hartree-Fock (HF) and Density Functional Theory methods in various basis sets. Weak chemical interactions were estimated enough well using HF/6-31G for a comparison of various geometrical conformations of these complexes. Energy of formation evaluation in charge-transfer complex C₆₀ +TTF is performing additionally calculating complex with far-separated molecules.     

Some New Aspects of Chlorination of Fullerenes

Abstract

The effect of the reagent ratio, reaction time and power of the reagent on the product composition in chlorination of [60]fullerene was studied. Chlorofullerenes C₆₀Cl₆, C₆₀Cl₈, C₆₀Cl₁₀, C₆₀Cl₁₂, C₆₀Cl₁₄, and C₆₀Cl₂₆ were synthesized and characterized by chemical analysis, FTIR, ¹³C NMR, and MALDI TOF mass spectrometry. The experimental data supported the coexistence of several isomers of C₆₀Cl _n (n = 8, 10, 12, 14, 26); the mixtures were not separated so far. Semiempirical calculations (AM1, PM3) were used to analyze the addition patterns and resulted in the most favorable structures of C₆₀Cl_8–26. Chlorination of C₇₀ under various conditions invariably yielded C₇₀Cl₁₀.     

Superstructures of Polymeric Stars with Fullerene Core in Solutions

Abstract

Poly(styrene) stars (PS)₆C₆₀, twin‐cores (PS)₆C₆₀‐[Si‐(CH₃)₂]‐C₆₀(PS)₆ and hybrids (PS)₆C₆₀(PTBMA)₆ with paired arms of PS + poly(tertbutylmethacrylate) have been studied in toluene (20°C, concentration C = 1–6 wt.%) by small‐angle neutron scattering (SANS) at momentum transfer q = 0.001–5 nm^?1. The C₆₀ stabilize arms' stretched conformation and intensify stars' ordering. While the (PS)₆C₆₀ and hybrids formed tiny clusters (particles' number N ～ 10–80, size R _C ～ 50–100 nm), the dimers created massive structures (N ～ 1 · 10³–2 · 10³, R _C ～ 300 nm) that can be induced by dipolar interaction of C₆₀ twin‐cores.     

Determination of water in pressurized pharmaceutical metered dose aerosol products

Abstract

An easy, rapid and reproducible method for the determination of a low level of water content in pressurized metered dose aerosol products is described. A Mitsubishi Moisture Meter Model CA-06 with Karl Fischer reagent was used for this study. The sample can be introduced into the reagent chamber through the septum plug using a syringe needle from the valve of sample canister. One determination takes 2～3 minutes and the results are accurate and reproducible (CV=2～6%) in the range of 10～30 ppm, H₂O. The linear correlation coefficient was 0.9994 in the range of 50-200 μg of H₂O.