Synthesis of C60-NBN and C70-NBN(N=L, 2) by DC arc Burning Method

Abstract

Macroscopic quantities of boron-doped fullerenes, such as C_60-nB_n and C_70-nB_n(n = 1, 2), were successfully synthesized by DC arc burning method, extracted by CS₂, and characterized by field desorption mass spectra. Among them C₅₈B₂ and C₆₈B₂ were extracted for the first time. The boron-doped fullerenes were found to be less stable than their pristine fullerene analogs. When the electric current becomes too high, no boron doped fullerene, but more higher fullerenes, were formed.     

A STUDY ON THE THERMAL STABILITY TO 1000°C OF VARIOUS CARBON ALLOTROPES AND CARBONACEOUS MATTER BOTH UNDER NITROGEN AND IN AIR

The thermal behavior of graphite, C₆₀ fullerene, fullerene black (carbon soot containing fullerenes), extracted fullerene black and diamond has been analyzed to 1000°C by TGA-DTA (thermogravimetric analysis and differential thermal analysis) under a nitrogen flow at a heating rate of 20°C/min. Very small weight losses have been recorded in the case of graphite and diamond. Furthermore no diamond graphitization has been observed. The sublimation of pure C₆₀ and the fullerene fraction of fullerene black (both pristine and extracted) has been observed and discussed.

The combustion reaction in air flow of graphite, C₆₀ and C₇₀ fullerenes, fullerene black (both unextracted and extracted), carbon nanotubes and diamond has been studied by TGA-DTA at a heating rate of 20°C/min. C₇₀ fullerene and fullerene black have been found to be the most reactive carbon materials with O₂. The role played by C₇₀ in the degradation of fullerites has been discussed. Among the carbon materials examined, the best resistance to O₂ attack has been shown by diamond and carbon nanotubes. The behavior of graphite is intermediate between diamond and fullerene blacks. The behavior of C₆₀ fullerene appears closer to that of graphite although it appears to be more reactive with O₂. Samples of graphite and carbon blacks N375 and N234 have been studied by TGA-DTA in air flow before and after a radiation treatment with neutrons or γ radiation. The effect of the radiation damage in the combustion reaction of these carbon materials has been discussed.     

Raman Spectra of Chlorinated C60 and C70 Fullerenes

Raman spectra of chlorinated C₆₀ and C₇₀ fullerenes prepared by photochlorination have been reported and discussed. The Raman lines suggest structural analogies with already fully characterized brominated fullerenes. Intense laser light irradiation cause a decomposition of fullerene chloro-derivatives leading to the formation of C₆₀ polymer.     

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.     

C60 and Giant Fullerenes in Soot Condensed in Vapors with Variable C/H2 Ratio

A transmission electron microscope (TEM) study of individual soot grains forming fluffy carbon particles produced using the arc-discharge technique revealed close-packed arrangements of single-wall ring structures with average diameters of 0.7, 1.1, 3.0, 5.5, and 8.2 nm. These structures were hypothesized to be C₆₀ and giant, C₅₄₀, C₉₆₀, and C₁₅₀₀, fullerenes that could form by coalescence during condensation and soot agglomeration, although in situ solid-state growth cannot be excluded. Mass spectroscopy and high performance liquid chromatography (HPLC) chromatography of the samples confirmed the presence of C₆₀ fullerene in all samples giving confidence to the giant fullerene growth scenario. Our results suggest that fullerenes could be common in soot grains produced by this technique as well as being an important carbon phase in C-rich accretion disks around young stellar objects and among the dust in the interstellar medium.     

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.     

Fullerene Research in Poland

Main results of the investigations of fullerene and its derivatives are briefly reviewed. Such topics as plasma spectroscopy, fullerenes and nanotubes formation, C₆₀ carbyne knots, fullerene reduction and doping, charge transfer states and electroabsorption of C₆₀, electrical conductivity, superconductivity, ESR properties, fullerene clathrates, C₆₀/C₇₀ complexes with organic donors, fullerene adducts, hydrogenated fullerenes, metallofullerenes and carbon nanotubes are discussed.     

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.     

SIMULTANEOUS DETERMINATION OF C60 AND C70 FULLERENES BY A SPECTROPHOTOMETRIC METHOD

In all fullerene-producing systems, reaction products were black soot extracts reported to contain a 5-25% fullerene mixture. Toluene extraction of the soot results in a solution of C₆₀, C₇₀, and higherc fullerenes. Without separation, absolute determination of the contents is not possible, leaving the researcher to comment only on the C₆₀/C₇₀ ratio of the solution. High-performance liquid chromatography, nuclear magnetic resonance, and scanning tunneling microscopy imaging techniques were reported in the literature for determining the C₆₀/C₇₀ ratio of the mixtures. These methods require tedious experiments and produce slightly differing results as well. In this communication, a new and relatively quick method is proposed for the simultaneous determination of the yields of C₆₀ and C₇₀ (not the ratio) in fullerene-containing solutions by ultraviolet-visible spectrophotometric 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.     

Stone-Wales Rearrangement Pathways from the Hinge-Opened [2+2] C60 Dimer to Ipr C120 Fullerenes. Vibrational Analysis of Intermediates

Possibility of the previously proposed hinge-opened product 2 of [2+2] C₆₀, dimer 1 transforming itself into IPR C₁₂₀ fullerenes by a series of generalized Stone-Wales (GSW) rearrangements has been tested by seeking all topologically acceptable pathways with the help of a graphical search program. the first IPR isomer 4 appeared after 20 GSW steps from the wide-bridged dumb-bell shaped precursor 3. More than 1,000 C₁₂₀ fullerene structures were generated during subsequent ten GSW steps, but the outstanding T_dC₁₂₀ global minimum 5 was not reached. Semiempirical vibrational calculations predict characteristic transition in the vibrational spectra in the course of rearrangement pathway.     

Instrumental Neutron Activation Analysis of Trace Element Impurities in Graphite Soot, Gold Grade C60 and C70 and in Super Gold Grade C60

Actually the purity of fullerenes is in general characterized as the percentage of the main component (e.g. C₆₀) versus the higher fullerenes (e.g. C₇₀, etc.) and/or in a few cases of some other polycyclic organic components.

We are reporting here for the first time detailed data on trace element impurities in fullerene precursors and in the main fullerenes. For studying the element impurities instrumental neutron activation analysis (INAA) was used. Our measurements have shown that all these materials contain trace elements at ppb (ng/g) ami ppm (μg/g) levels. From the results it comes (Hit that in the future investigations of the elemental purity of the C₆₀ and C₇₀, and even of the higher fullerenes would have to be also considered when their electrical, magnetic, etc. properties are studied.     

Which Fullerene Is Appropriate to Host C20? A Molecular Modeling Study

Molecular mechanics (MM) and molecular dynamics (MD) study of fullerene complexes of the short-lived “smallest fullerene” C₂₀ with icosahedral C₆₀, C₈₀, C₁₄₀, C₁₈₀, and C₂₄₀ of I_h, I_h, I, I_h, I_h symmetry, respectively, using CVFF and ESFF forcefields revealed that the most stable complexes can be formed only if the intershell distance between fullerenes is similar to that in graphite or in experimentally observed buckyonions. The fullerenes C₁₄₀ and C₁₈₀ are the smallest suitable candidates to form such complexes with C₂₀. Similarly to the stabilization of short-lived cyclobutadiene or benzyne in hemicarcerands, C₂₀ is expected to be stabilized inside the C₁₄₀ and C₁₈₀ cages which would enable a deeper understanding of the highly nonplanar system of conjugated bonds of this exotic molecule.     

Ozone Reaction with C70 and C60 Fullerenes: The Effect of Temperature on the Reaction Kinetics

It has been confirmed that the effect of temperature on the rate constants (k) of ozone reaction with C₇₀ and C₆₀ fullerenes follows the Arrhenius law. The experimental values of activation energy (E_a) and pre-exponential factor (A), like as those of other simple alkenes, are in the order of 2.4-2.6 kcal mol^-1 and (1.2-1.8) × 10⁷ L mol^-1 sec^-1, respectively. They are practically equal for the both fullerenes. It has also been found that the value of the rate constant k of C₇₀ fullerene ozonolysis is higher in comparison to the respective k-value of C₆₀.     

ON THE MECHANISM OF CARBON CLUSTERS FORMATION UNDER LASER IRRADIATION. THE CASE OF DIAMOND GRAINS AND SOLID C60 FULLERENE

It is shown by FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometry that carbon clusters considered to be the superior homologues of C₆₀ fullerene are formed by laser irradiation of both synthetic diamond grains or from pure C₆₀ fullerene crystals. The surfaces of the laser irradiated diamond or C₆₀ have been examined by Raman spectroscopy. In the case of diamond the Raman spectrum suggests the superficial formation of mixed carbon nanostructures consisting of disordered graphite, fullerenic nanostructures, onion-like carbon nanostructures and diamond-like carbon. Based on the Raman spectra of the surface and on data taken from the phase diagram of carbon, it is shown that the graphitization is needed in order to produce fullerenes from diamond under laser ablation conditions. In the case of C₆₀ fullerene, it is shown by Raman spectroscopy that the laser irradiation of the crystals causes initially their photopolymerization and after further irradiation their transformation into disordered graphite. Based on these results and on a literature survey on the formation of fullerenes from more than 15 completely different substrates, it is concluded that fullerenes are formed always when laser ablation leads to a graphitization of the laser-irradiated substrate. Some astrochemical implications of the conclusions have been discussed.     

CO-DEPOSITION OF FULLERENES AND SULFUR FROM DILUTED SOLUTION

A new method to synthesize fullerene and sulfur compounds has been developed. Using this method, C₆₀S₁₆ and C₇₀S₁₆ compounds were grown from dilute fullerene and sulfur toluene solution. Their atomic structures were analyzed by x-ray diffraction with the single crystal. The C₆₀S₁₆ crystal is C-centered monoclinic structure of a=2.0874 nm, b=2.1139 nm, c=1.05690 nm and β=111.93°, and the C₇₀S₁₆ has a primitive monoclinic, P2₁/c, with lattice parameters of a=1.5271 nm, b=1.49971 nm, c=2.18024 nm and β=109.791°. In this compound, the structure of fullerenes is maintained and sulfur atoms form S₈ rings placed around the fullerenes.     

Phenylamine Analogous Adducts of C60

Reaction conditions leading to efficient nitration of the C₆₀ molecules for the production of nearly pure hexanitro[60]fullerenes using gaseous nitrogen dioxide as the nitration agent were developed. Approach of utilizing hexanitrofullerene as a reactive precursor molecule in the preparation of organic derivatives of C₆₀ demonstrated a versatile alternative synthetic method for indirect fullerene functionalization. Fullerenic nitro functions were found to be excellent leaving groups opt for replacement by nucleophilic substituents, such as phenylamine and oligophenylamines.     

The Effects of Radicals on the Formation of Fullerene Ions in Laser Desorption Studies of C60 Adducts

We have studied the fragmentation and aggregation of C₆₀ and its radical adducts R_nC₆₀ by laser-desorption TOF mass spectrometry in the positive and negative ion channels. The mechanism of the formation of daughter fullerenes in the negative ion channel and the enhancement of fullerene aggregation products have been discussed. We consider that the electron transfer process between neutral cage-like clusters and the radicals is responsible for the appearance of strong mass peaks of daughter fullerene anions in the case of C₆₀ radical adducts. The effects of the radicals on the fullerene aggregation process have been discussed.     

Fullerenes in the Fossil of Dinosaur Egg

By means of laser desorption post-ionization time-of flight mass specrometry (TOF) and high-pressure liquid chromatography (HPLC), fullerene C₆₀ have been found in a fossil of dinosaur egg shell from Xixia (N_33.3 E_111.4), China. These techniques verified also mat fullerene C₇₀ is virtually absent from identical egg fossil of dinosaur at XiXia. Preliminary results suggest that C₆₀ occurrence and C₇₀ absence may be the outcome of environment (ambient temperature, and SO₂ pollution of Earth's atmosphere, etc.) effects during the synthesis of fullerenes at 70 million years ago.     

The Dark Reaction of C60 and of C70 with Molecular Oxygen at Atmospheric Pressure and Temperatures between 300 K and 800 K

The solid fullerenes C₆₀ and C₇₀ react in deliberate and adventitious situations with molecular oxygen in a wide range of temperatures. Using thin films and polycrystalline bulk samples with well-defined structures and chemical histories we investigated the complex process from molecular intercalation over atomic adduct formation to deep oxidation and polymerisation which together describe the oxidation reaction. A combination of photoemission (UPS, XPS) photoabsorption (XAS), FT-IR, temperature-programmed and isothermal gravimetric measurements and DSC allowed to identify the existence and gradual interconversion of the three types of solid products besides the gas phase products CO and CO₂. Both fullerenes react along the same reaction path. The difference of the molecular structures results in different activation barriers in the initial step of intercalation and in the final step of cage-opening. The overall reactivity of both fullerenes is quite similar at temperatures above the gasification onset of 570 K. The formation of the various adduct compounds was found to exert a detectable influence upon the overall molecular shape of the fullerenes and a small effect on the electronic structure was observed. The only moderate differences in electronic and geometric structures of pristine and initially oxidised fullerenes precludes a pronounced molecule-by-molecule reaction control and allows the topochemistry of the intercalation to control the shape of the reaction interface. This control is less effective for C₇₀ than for the C₆₀ fullerene.