Possible Reaction Mechanism for the Formation of C60 From Naphthalene: A Semi-Empirical and Ab Initio Molecular Orbital Study

Mechanism of C₆₀ formation from naphthalenes was studied by quantum chemical calculations. a patch up process of T-shape dimerization of naphthalenes followed by the intramolecular ring fusion, all through radical reactions, was proposed for a possible mechanism for the C₆₀ formation from naphthalenes. the reaction barrier was found to be less than 60-70 kcal/mol for each reaction step in this mechanism.     

Spontaneous Decay of Highly-Charged Fullerene Ions C60Z+ and C58z+

Abstract

Using isotope-resolved, two sector field mass spectrometric techniques we have identified and investigated quantitatively the energetics and kinetics (in particular the kinetic energy release, KER) of the spontaneous decay reactions C_60–2m ^z+ → C_60-2m-p(z-1)+ ₊ C_p ⁺ with m = 0 or 1, z ranging from 3 to 6 and p = 2 and 4. The obtained KER results are not compatible with the properties expected for a single-step fissioning reaction as described by the liquid drop model. Therefore the present data had to be interpreted by a different fragmentation mechanism. This novel reaction sequence, termed auto charge transfer (ACT) reaction, is initiated by the statistically driven neutral C₂ (or C₄₎ evaporation followed by an electron transfer process from the receding C₂ (or C₄) fragment to the remaining highly-charged fullerene ion thereby leading finally to the two charged reaction products observed in the exit channel of the decay reaction. Moreover, in the case that a C₂ ⁺ loss from C₆₀z+ is occurring in the first field-free region we have been able to demonstrate that it is possible to observe in the second field-free region a subsequent C₂ evaporation from the C₅₈(z-1)⁺ fragment ion.     

FORMATION OF FULLERENES AND CARBON CLUSTERS BY LASER IRRADIATION OF POLYMERIC FULLERENE OXIDE (FULLERENE OZOPOLYMER)

ABSTRACT

Polymeric fullerene oxide (PFO) prepared by prolonged ozonation of C₆₀ fullerene has been laser irradiated and the resulting products formed have been studied by ion cyclotron resonance mass spectrometry. It has been found that PFO produces a complete set of carbon clusters from C₆₀ up to C₁₆₄. The mechanism of formation of this set of fullerenic clusters implies necessarily a laser-induced carbonization step of the PFO substrate. Once the PFO target has been changed into the opportune carbon nanostructure by the laser radiation, the sequence of fullerene carbon clusters has been produced.     

Catalytic Preparation and Characterization of C60Br24

Abstract

In this paper the procedure for catalytical bromination of C₆₀ with elementary bromine with FeBr₃ as a catalyst is described. In this procedures only one reaction product - C₆₀ Br₂₄ is obtained. The twenty four bromine atoms are symmetrically distributed over the C₆₀ sphere, which was confirmed by thermogravimetric analysis. The yield of bromine derivative in this reaction is 98%.     

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

Abstract

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.     

Quantum Chemical ab initio Investigations of Non-Covalent Bonding Derivatives of Fullerene C60 and Li Atom or Cs2, C6H6 Molecules

Abstract

Quantum chemical ab initio investigations of the stability of the non-covalent fullerene complexes: C₆₀ molecule + Li atom, two C₆₀, two C₆₀ + CS₂, C₆₀ + CS₂, C₆₀ + C₆H₆ were performed using Hartree-Fock (HF) and Density Functional Theory (DFT) methods in various basis sets. The inclusion of electron correlation effect calculated by using DFT B3PW91 model during the optimization of Li atom position above hexagonal of C₆₀ gives the smaller distance from the centre of C₆₀ equal to 7.75 Å and large positive energy of formation equal to 4.452 kcal/mol in comparison with HF calculated distance 8.39 Å and energy of formation 1.810 kcal/mol. The positive energy of formation equal to 0.483 kcal/mol for optimized complex two C₆₀ + one CS₂ was found by HF. The presence of CS₂ molecule stabilises this complex with the energy equal to 0.281 kcal/mol. Complexes: C₆₀ + CS₂, C₆₀ + C₆H₆ do not possess the positive energy of formation.     

Photo-Induced Cytotoxicity of Water-Soluble Fullerene

Abstract

The reaction of C₆₀ with poly(ethylene glycol) having a terminal primary amino group or a mixture of ethylene diamine and poly(ethylene glycol) having terminal carboxyl groups resulted in formation of water-soluble C₆₀ conjugates. These conjugates showed strong cytotoxicity to L929 cells upon visible light irradiation as a result of superoxide production.     

The Solid-State Mechanochemical Reaction of Fullerene C60

Abstract

The solid-state mechanochemical reaction of fullerene C₆₀ by the use of a high-speed vibration milling technique has been applied to the nucleophilic addition of an organozinc reagent to C₆₀, [4+2] cycloaddition of C₆₀ with condensed aromatic hydrocarbons, 1,3-dipolar addition of C₆₀ with organic azides, and dimerization of C₆₀.     

High Temperature Vaporization and Thermodynamic Properties of the Potassium - C60 Phases

Abstract

Knudsen cell mass spectrometry and simultaneous Knudsen-torsion effusion technique were used to study K/C₆₀ binary system. Activities of potassium and/or C₆₀ were measured in all heterogeneous regions of the K-C₆₀ phase diagram and the Gibbs energies of formation of K_xC₆₀(x=l, 3, 4, 6) were calculated. Gaseous species KC₆₀(g) was identified and the Gibbs energy of formation of KC₆₀(g) was calculated directly from the experimental data.     

Bromination of [60]Fullerene. I. High‐Yield Synthesis of C60Br x (x=6, 8, 24)

Abstract

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.     

Thermal Transformation of Ring-Opened [2+2] C60 Dimer into a Wide-Bridged C120 Isomer. A Computational Evaluation of Fulvalene-Naphthalene Rearrangements

Abstract

As a continuation of the studies on thermal transformation of the [2+2] C₆₀ dimer (1), the consequence of the pyracylene-rearrangement-like valence isomerization of the fulvalene partial structure at the bridge of the ring-opened product from 1, namely 2, was searched by dynamic reaction coordinate /AM1 semiempirical MO calculations. It is predicted that the fulvalene bridge of 2 rearranges into naphthalene partial structure by the concerted ‘in-plane’ mechanism to give a wide-bridged C₁₂₀ intermediate having twenty five-membered rings and two ten-membered rings (3). The computed energy of activation (145 kcal/mol) is 40 kcal/mol lower than those computed for pyracylene rearrangements. In contrast, the recently reported analogous rearrangement of indigo (13) to dibenzonaphthyridindione (14) is computed to occur by the stepwise ‘sp³’ mechanism.     

Catalytic activity of hybrid platinum nanoparticle-[C60]fullerene nanowhisker composites for 4-nitrophenol reduction

Abstract

Composites comprising platinum nanoparticles loaded on [C₆₀]fullerene nanowhiskers were prepared by a liquid-liquid interfacial precipitation method. The synthesized platinum nanoparticle-[C₆₀]fullerene nanowhisker composites were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The catalytic activity of the platinum nanoparticle-[C₆₀]fullerene nanowhisker composites was confirmed for the reduction of 4-nitrophenol by UV–vis spectroscopy. The reduction of 4-nitrophenol catalyzed by the platinum nanoparticle-[C₆₀]fullerene nanowhisker composites followed the pseudo-first-order reaction rate law.     

Trifluoromethylation of [60]- and [70]Fullerene in the Ionization Chamber of a Mass Spectrometer

Abstract

Both [60]- and [70]fullerene react with either the Scherer radical (perfluorodiisopropylethylmethyl, C₉F₁₉), a mixture of branched perfluorononenes (C₉F₁₈, the product of hexafluoropropene trimerization), or β-fluorosulphatotetrafluoroethyldiheptafluoroisopropylmethyl radical (C₉F₁₈OSO₂F) in the ionization chamber of a mass spectrometer to give the positive parent ions of trifluoromethylation products, the reaction being accompanied by hydrogen addition. The reaction occurs at least partly on the walls of the ionization chamber, by a radical mechanism employing CF₃ radicals formed from the radical reactants both thermally and under electron impact; only the latter route occurs with the perfluorononenes.     

Pulsed Laser Processing of Carbon and Silicon Clusters and Thin Films

Abstract

Several new processes have been developed for the preparation of fullerenes and thin films by using a pulsed excimer laser. The irradiation of a pulsed KrF excimer laser beam onto a C₆₀ powder target produced single phase C₆₀ thin films when the laser energy fluence was in the range between 40 and 50mJ/cm². By atomic force microscopy, the laser-deposited C₆₀ thin film was verified to have a surface far smoother that the surfaces of films produced by the conventional evaporation method. The stainless steel rods coated with this film exhibited an excellent tribological property. Cluster formation from SiC and other carbides MC_n(M=Ti,W,B) was investigated by laser desorption time-of-flight mass spectrometry. No clear indication was observed for the production of such clusters as (SiC)₆₀ and (M_xC_60-x) from the sintered targets directly as well as from the films laser deposited from the targets. However, C₆₀ and C₇₀ were found to exists in the laser-deposited films, indicating a new applicability of pulsed laser processing for segregative cluster synthesis from solid solution. Preliminiary results on thin film deposition via pulsed ablation of (Ba,Na)_xSi₄₆ clathrate were also presented.     

Chlorosulphonyl Group as a New Functionality on Fullerenes: [2+2]-Cycloaddition of Chlorosulphonylisocyanate to C60

Abstract

The chlorosulphonylisocyanate reacts smoothly with C₆₀ in xylene under thermal conditions in a [2+2]-cycloaddition fashion to yield the bisadduct as one of the products in the inseparable reaction mixture. The reaction product is analysed by FAB-MS, ¹³C NMR, FT-IR and HPLC techniques. Results show the formation of imino-lactone as one of the favourable products.     

Intermolecular Interaction of [60]Fullerene with Tröger's Base Analogues

Tröger's base (TB, 1) and its analogues were synthesized and were subject to the titration experiments to evaluate their ability of supramolecular complexation with C₆₀. Results demonstrate clearly that the fluorene-based TB analogue (2) and the bioctylfluorene-based TB analogue (3) show 1:1 binding with C₆₀ to form the corresponding complexes while TB 1 does not. Titration experiments exhibited that the association constant (K_ass) of 3/C₆₀ (48.1 ± 7.9 M ^?1) was larger than that of 2/C₆₀ (13.7 ± 1.4 M ^?1)_. The formation of the 1:1 binding complexes 2/C₆₀ and 3/C₆₀ was also confirmed by MALDI-TOF mass spectrometry. Theoretical calculations suggest that 2 and 3 have appropriate cavities to embrace C₆₀. These findings indicate that not only the π/π interaction between the fluorene moieties and the C₆₀ surface but also the CH/π interaction between the octyl groups and the C₆₀ surface serve efficiently in the supramolecular complexation with C₆₀.     

GENERATION OF HIGHER FULLERENES FROM LASER ABLATION OF CARBYNE AND C60 PHOTOPOLYMER ASTROCHEMICAL IMPLICATIONS

ABSTRACT

Laser ablation of targets of carbonaceous matter containing carbyne nanodomains (the sp hybridised carbon chains) or targets of C₆₀ photopolymer produced carbon clusters which have been detected by FT-ICR (Fourier-Transform Ion Cyclotron Resonance) mass spectrometer. When the carbonaceous matter containing carbyne has been employed as laser target, no C₆₀ has been generated but only fullerene cages from C₇₄ up to C₁₂₄. Larger cages were also obtained but with odd number. Starting from C₆₀ photopolymer, laser ablation regenerates free C₆₀ and creates a sequence of C₆₀ superior homologues all possessing even number and each member of the series is separated from the preceding and the following member by the loss or by the addition respectively of a C₂ unit. Fullerenes up to C₁₆₂ have been recorded. The implications about the presence of free C₆₀ fullerene in the interstellar and circumstellar space, its formation from carbyne chains and its stability towards its photopolymerization tendency and its regeneration from the photopolymer together with its superior homologues have been discussed thoroughly in the present paper.     

Transport Properties of Fullerene–Polyphenylene Oxide Homogeneous Membranes

Abstract

Fullerene–polyphenylene oxide (C₆₀–PPO) compositions containing up to 2 wt% C₆₀ were obtained and used for homogeneous membranes formation. Gas separation properties were estimated by measuring the permeability of individual gases H₂, O₂, N₂, CH₄, and CO₂. A correlation between gas permeability and free volume was established. The pervaporation of water/ethanol mixtures through fullerene‐containing membranes showed that C₆₀–PPO membranes exhibit dehydration properties. The degree of equilibrium sorption for PPO and C₆₀–PPO membranes in a water/ethanol system was estimated in the liquid phase. Gas separation and pervaporation properties were treated as a reflection of molecular interactions between PPO and C₆₀ molecules in compositions.     

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

Abstract

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.     

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.