Determination of C60 and/or C70 Concentrations

Two methods of quantitative analyses of the fullerenes C₆₀ and C₇₀ are described. Quantitative Infrared Spectroscopy permits the determination of the concentrations of pure and mixed compositions of C₆₀ and C₇₀ in carbondisulfide solutions. Alternatively, the ratio of C₆₀/C₇₀ is analyzed by evaluating the lattice parameters of a solid solution of the fullerene species and cyclohexane according to Vegard's Law. Both methods show high accuracy and are suited for calibration of mass spectrometric analyses of fullerene samples.     

Natural Fullerenes-Will they Offer a Hint to the Selective Synthesis of Fullerenes?

In addition to the known laboratory methods of preparing fullerenes, which generally start from carbon vapor, studies of naturally occurring C₆₀/C₇₀ suggest a catalytic process of fullerene formation that proceeds in solid phase under mild condition. Recent observation of C₆₀/C₇₀ in Yunnan coal and Kalerian C-rich rock is reviewed in the light of the above perspective.     

THE ELUSIVE C60S: THREE ATTEMPTED SYNTHESES

Results of semiempirical energy calculations suggested that a [6,6]-closed C₆₀S fullerene sulfide might be stable. Attempts were therefore undertaken to synthesize the compound by UV photolysis of C₆₀ in CS₂ and by the heating of mixtures of C₆₀ and S₈ to 325 and 400°C. Any sulfide, if formed, was present in undetectably small quantities. However, [¹²C₆₀³⁴S]^- ions were observed when a mixture of solid C₆₀ and elemental sulfur was analyzed by Laser Desorption Ionization Time-of-Flight mass spectrometry.     

Raman Spectroscopy of the Charge Transfer Complex (TTF)x C60 Br8

We report Raman studies on powder samples of the charge transfer complex (TTF)_x C₆₀Br₈ at room temperature. The phonons show considerable softening with respect to the frequencies observed in the Raman spectrum of solid C₆₀ Brg. The strongest mode at 1464 cm^-1 in C₆₀Br₈ is red shifted to a doublet with peaks at 1414 and 1421 cm^-1, implying an average phonon softening Δω of -47 cm^-1. A comparison with the phonon softening of the corresponding A_g(2) mode in alkali-doped C₆₀ (Δω ~ - 36 cm^-1 for A₆C₆₀, A = K, Rb or Cs) suggests that 8 electrons are transferred per C₆₀Br₈ molecule in the charge transfer complex. The mode at 503 cm_--1 in C₆₀Br₈ is shifted upwards, similar to that in A₆ C₆₀ compounds.     

Halogen and Interhalogen Reactions with [60]Fullerene: Preparation and Characterization of C60C24 and C60C18F14

U.V. irradiation of a solution of [60]fullerene in carbon tetrachloride saturated with chlorine gave a yellow solid, the negative ion FAB mass spectrum of which is consistent with the presence of C₆₀Cl₂₄ When a solution of [60]fullerene in CCl₄was mixed with IF₅, a yellow solid was deposited in the denser IF₅ layer. The negative ion FAB mass spectrum of this material indicated it to be C₆₀C₁₈F₁₄ This result provides the first confirmation that halogenation of Merenes is a radical process. Fluorination of C₆₀Br₈ gave a range of fluorinated products, having a maximum fluorine content of ca. 36 fluorines per cage, and with either C₆₀F₁₈ or its mono-oxide as major species. EI mass spectrometry of the products at various temperatures indicates that the more highly fluorinated fiiilerenes are either less stable to heat, or are more volatile.     

Studies on Fullerenes Using Positron Annihilation Spectroscopy

Results of positron lifetime measurements as a function of temperature and pressure are presented. With the application of pressure, the lifetime in solid C₆₀ is observed to decrease and show signatures of the structural transition from fcc to the simple cubic (sc) phase. Positron lifetime measurements as a function of temperature, carried out in both C₆₀ and C₇₀, indicate an increase in lifetime at elevated temperatures. This is accounted for in terms of thermally activated trapping of positrons from the interstitial regions to the open regions within the cage structure. In addition to studies in the solid state, the annihilation characteristics of the ortho positronium (O-Ps) formed in organic solvents has been monitored with increasing concentration of dissolved fullerenes, C₆₀ and C₇₀. The observed reduction of the ortho positronium lifetime is understood in terms of the formation of O-Ps- Fullerene complex prior to annihilation.     

C60H18, C60H36 and C70H36 Fullerene Hydrides: Study by Methods of IR, NMR, XPS, EELS and Magnetochemistry

Fullerene hydrides of C₆₀H₁₈, C₆₀H₃₆ and C₇₀H₃₆ are studied by using IR, ¹H and ¹³C NMR, X-ray photoelectron and electron energy loss spectroscopies, and magnetochemistry. The comparison of IR and solid state ¹H and ¹³C NMR data for C₆₀H₃₆ with the theoretical ones allows the suggestion that fullerene hydride has a T symmetric structure and contains 4 isolated benzenoid rings located at tetrahedral positions on the surface of a closed skeleton of the molecule. The EELS revealed that the transition from fullerene to the hydride is accompanied by the decrease of the density of valence electrons. Magnetization measurements showed C₆₀H₃₆ to be a ferromagnet. The hydrogenated fullerenes were prepared by transfer hydrogenation procedures involving 9,10-dihydroanthracene. The compositions of the hydrides are determined by field desorption mass-spectral analysis.     

Investigations of the Interaction of Nickel and Carbon Monoxide with Solid Films of C60 and C70 by UV and X-Ray Photoelectron Spectroscopy

Based on UV and X-ray photoelectron spectroscopy, it is shown that nickel metal clusters deposited on solid C₆₀ and C₇₀ films cause marked changes in the valence band spectra. In addition, the C 1s core-level of the fullerenes shift to lower binding energies while the Ni 2p_3/2 core level shifts towards higher binding energies, especially at small metal coverages. These observations signify the occurrence of charge-transfer from the nickel metal to the fullerene. We also show that CO adsorbs weakly on C₆₀ and C₇₀ surfaces.     

Radiation-Induced Trichloromethylation of C60 Fullerene in Carbon Tetrachloride

The radiolysis of C₆₀ in CCl₄ has been studied in detail from the organic chemistry point of view. Solutions of C₆₀ in CCl₄ have been treated with γ radiation at 25, 50, 150, and 600 kGy, and the resulting products have been studied by electronic absorption spectroscopy, FT-IR spectroscopy, solid state ¹³C-MAS-NMR and by thermogravimetric analysis. The products have also been separated by liquid chromatographic analysis (HPLC). C₆₀ undergoes a multiple trichloromethylation reaction and on average about 6 trichloromethyl radicals add to the fullerene cage. The trichloromethylation reaction is accompanied by the dimerization and trimerization of C₆₀ fullerene. Also the oligomers appear to be trichloromethyl-substituted.

For reference the C₆₀ solutions in CCl₄ have also been photolyzed with UV light. Similar product as those observed in the radiolysis experiment have been detected. The main difference is that the photolysis products appear both chlorinated and trichloromethylated while the radiolysis product appear almost exclusively trichloromethylated.     

MOLECULAR DYNAMICS SIMULATIONS OF PREFERRED ORIENTATIONS IN THE HIGH TEMPERATURE PHASE OF C60

Molecular dynamics simulations of the high temperature phase of C₆₀ have been performed for different intermolecular potentials proposed previously for the intermolecular interactions in solid C₆₀, i.e. the van der Waals (vdW) potential and two different bond charge models. In contrast to what has been previously inferred from a mean-field theory, bond charges do lead to a much better reproduction of the experimental results, including the preferred orientations of the C₆₀ molecule, than the vdW potential.     

Synthesis and Spectral Characterization of Difunctional Fullerenes

The oxidation of C₆₀ with m-chloroperbenzoic acid gave C₆₀O₂ with a high positional selectivity, as the ¹³C NMR analysis suggested. Diadducts C₆₀CCI₂O, C₆₀CCl₂(anthracene), C₆₀CCl₂[(CH₂CH₂)₂N₂], and C₆₀CCI₂[Pt-(PPh₃)₂] were synthesized, isolated, and characterized by negative ion FAB mass spectroscopy.     

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

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.     

Electronic structure and electrical transport characteristics of C60, 2C60 and 4C60 fullerene molecules

The extended H?ckel method and the Green s function method were used to calculate the electronic structure and electrical transport of Au electrode-C₆₀, 2C₆₀ or 4C₆₀ fullerene-Au electrode systems. Furthermore, their electronic structure and electrical transport characteristics were compared and analyzed. The results show that (i) owing to the contact with the Au electrodes, the C₆₀, 2C₆₀ and 4C₆₀ molecules change in their electronic structures significantly, and their energy gaps between LUMO and HOMO are narrow; (ii) the bonding between C₆₀, 2C₆₀ or 4C₆₀ fullerene and Au electrodes is partially covalent and partially electrovalent; and (iii) the conductance of the three fullerenes conforms to the order of C₆₀>2C₆₀>4C₆₀.     

GROUP TRANSFER AND DIMERIZATION PROCESSES OF C60(CN)2 UNDER ATMOSPHERIC PRESSURE IONIZATION CONDITIONS

Neutral and anionic C₆₀(CN)₂ were investigated with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) mass spectrometry. It was observed that its anions underwent cyano- group and oxygen transfer, and dimerization processes in ESI conditions to form C₆₀(CN)₃H^-, C₆₀(CN)₂(OH₂)^-, [C₆₀(CN)₃H]^-₂, [C₆₀(CN)₂(OH₂)]^-₂ and [(C₆₀)₂(CN)₂(OH)]^-. Meanwhile, neutral C₆₀(CN)₂, for which no signal was observed in ESIMS, showed a base peak corresponding to C₆₀(CN)₂Cl^- in APCIMS spectra with CHCl₃ used as solvent, while only a molecular ion peak corresponding to C₆₀(CN)^-₂ was observed for the toluene solution of neutral C₆₀(CN)₂ in the same conditions. Possible mechanisms for group transfer and dimerization were proposed based on these observations.     

UNSTABLE PRODUCTS FROM THE OZONATION OF C60 IN SOLVENTS

The ozonation of a solution of C₆₀ in toluene results in the formation of several unstable compounds C₆₀X and C₆₀Y[1-5] which decay completely at room temperature within about 1 h. The products are oxides C₆₀O[6,6], C₆₀O₂[I], C₆₀O₂[II], and possibly an isomer of C₆₀O₃. The transformations are not due to oxidation by atmospheric oxygen but are spontaneous. The ozonation of a solution of C₆₀O[6,6] in toluene results in the formation of two unstable compounds C₆₀Z[1-2] which also decay completely to C₆₀O₂[I] and C₆₀O₂[II]. It is suggested that all unstable “parents” are ozonides.     

Bromination of [60]Fullerene. I. High-Yield Synthesis of C60Brx (x=6, 8, 24)

The systematic study of the bromination of C₆₀ was performed under various experimental conditions. Application of some chloroarenes as reaction media resulted in the high-yield (70-96%) selective synthesis of C₆₀Br₆ and C₆₀Br₈. Direct bromination of fullerene yielded either C₆₀Br₈, C₆₀Br₁₄, or C₆₀Br₂₄ depending on the reaction time. Possible pathways of bromination of C₆₀Br₈ were analyzed using semiempirical (AM1) calculations, two most probable molecular structures are conjectured for the first isolated C₆₀Br₁₄.     

Addition Reactions of Benzyne, Dienes, Dichlorocarbene, and Oxygen to C60

Benzyne was found to add to C₆₀ in good yield to give C₆₀(C₆H₄)_n (n=1-4). Typical Diels-Alder dienes were also found to add to C₆₀ under thermally mild conditions. Adducts of C₆₀ with 2,3-dimethylbutadiene, cyclopentadiene, hexa-chlorocyclopentadiene, 1,3-diphenylisobenzofuran, and anthracene were obtained. Further reactions of these products such as elimination and autooxidation reactions were investigated. Addition reaction of dichlorocarbene to C₆₀ gave C₆₁Cl₂. Oxidation of C₆₀ with m-chloroperbenzoic acid gave C₆₀O_n(n=1, 2). All of the products were isolated by means of HPLC and characterized by mass spectroscopy.     

聚乙烯亚胺修饰富勒烯的制备及其对聚丙烯热氧稳定性的影响

利用聚乙烯亚胺(PEI)分子中活泼的?NH?与富勒烯(C₆₀)结构中C=C键之间的加成反应,制备了PEI修饰C₆₀杂化物(C₆₀?PEI),并采用FTIR、TEM等测试方法对C₆₀?PEI的分子结构和形态进行表征。采用熔融共混法制备了C₆₀?PEI/聚丙烯(PP)复合材料,并对其热性能和阻燃性能进行研究。热失重分析结果表明,C₆₀?PEI可以更有效地发挥C₆₀的自由基捕捉作用,对PP热稳定性的提高效果较C₆₀更明显;氧化诱导测试(OIT)结果表明,C₆₀?PEI/PP复合材料比C₆₀/PP复合材料具有更优异的抗氧性能;微型量热测试也表明,燃烧过程中C₆₀?PEI/PP复合材料比C₆₀/PP复合材料具有更低的热释放量。      

Arylation of [60]Fullerene with Br2/FeCl3/PhH: Formation of C58 Derivatives via CO Loss

Heating a mixture of [60]fullerene, bromine, ferric chloride and benzene under reflux for 24 h products a range of phenylated [60]fullerene derivatives. The main product is C₆₀Ph₅H but other components identified by mass spectrometry (and in some cases separated by HPLC) are: C_6oPh_n(n = 4, 6, 8, 10, 12), C₆₀Ph_nO₂(n = 4, 6, 8, 10, 12), C₆₀Ph_nOH (n = 7, 9, 11), C₆₀Ph_nH₂ (n = 4, 10), C₆₀Ph₄H₄, C₆₀Ph₅H₃, C₆₀Ph_n0₂H (n = 5, 9), C₆₀Ph₄C₆H₄O₂, C₆₀Ph₉OH₃, and C₆₀Ph₁₁ O₃H₂. In the corresponding reaction with toluene, the crude reaction mixture contained C₆₀(MeC₆H₄)₄ as a main product; C₆₀(ClC₆H₄)₅H was obtained from the reaction with chlorobenzene. Formation of these derivatives is believed to involve radical bromination of the fullerene, followed by electrophilic substitution of the hatogenofullerene into the aromatic, accompanied in some case by hydrolysis, elimination and epoxide formation; oxidation may also introduce ketone/dioxetane functionality. The EI mass spectra of C₆₀Ph₄O₂ and C₆₀Ph₈O₂show degradation to C₅₈Ph_n (n = 0-8), having structures believed to be related to the pseudofollerenes C₆₈Ph_n (n = 0-8) reported recently. These results suggest that some derivatisations of fullerenes confer stability, due to the relief of strain.     

Detection of Buckminsterfullerene in Usual Soots and Commercial Charcoals

It was confirmed that soot produced by free burning of small hydrocarbons like benzene and cyclohexane generally contains less than 0.1 ppm of C₆₀. Small, but measurable amounts of C₆₀ were found in two samples of charcoal, providing the first indication of fullerene formation in the solid state.