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.     

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.     

Catalytic Preparation and Characterization of C60Br24

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%.     

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.     

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.     

Synthesis of Radiolabeled Fullerenes C60 and C70

The synthesis of radiolabeled C₆₀/C₇₀ for potential biochemical tracer studies was carried out. Vaporization under plasma are conditions (~3000C) of graphite rods impregnated with the ¹⁴C labeled steroid progesterone generates the expected C₆₀/C₇₀ mixture. Isolation and characterization of the ¹⁴C-C₆₀ is reported. Interestingly, the C₇₀ had more radioactivity than the C₆₀.     

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.     

Some New Aspects of Chlorination of Fullerenes

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.     

软模板导向合成多级孔丝光沸石及其苯的苄基化催化性能

通常认为丝光沸石是具有一维孔道结构的微孔沸石, 在涉及大分子的催化反应中存在较为严重的扩散限制。以双季铵型表面活性剂C₁₈H₃₇N⁺(CH₃)₂C₆H₁₂N⁺(CH₃)₂C₆H₁₃(Br^-)₂(C_18-6-6Br₂)作为软模板, 在水热条件下制备了多级孔丝光沸石分子筛。采用XRD、FT-IR、SEM、TEM、TG-DTG、N₂物理吸附、NH₃-TPD等手段对样品的晶体结构和物化性能进行了表征。结果表明, 加入C_18-6-6Br₂制备了纳米棒定向排列的多级孔丝光沸石, 而且可通过改变合成体系中C_18-6-6Br₂/SiO₂的比值, 对样品的晶粒尺寸、介孔表面积和介孔孔容进行系统调变。在苯与苯甲醇的苄基化反应中, 多级孔样品比传统微孔丝光沸石表现出更好的苄基化反应催化性能和显著提高的反应速率。多级孔丝光沸石优异的催化性能归因于介孔的存在使其具有更多的可接近活性位和更优异的质量传输性质, 这种独特的多级孔丝光沸石在大分子催化转化反应中具有较大的应用潜力。     

Fullerane, the Hydrogenated C60 Fullerene: Properties and Astrochemical Considerations

Hydrogenated C₆₀ fullerene, C₆₀H₃₆ was prepared in different solvents using Zn/HCl as reducing agents. The structure of C₆₀H₃₆ was confirmed both by electronic and FT-IR spectroscopy and the purity of the reaction product was checked by HPLC analysis. It has been confirmed that C₆₀H₃₆ is not stable in air, especially in presence of light which enhances the oxidation. The oxidation of C₆₀H₃₆ was studied by FT-IR spectroscopy and by differential scanning calorimetry (DSC) in air; the formation of hydroxyl groups on the fullerene cage and ketonic groups (involving cage breakdown) have been detected. Furthermore, the action of O₃ on C₆₀H₃₆ was investigated and it has been found that O₃ exerts practically the same effect of air but causing an enhanced cage breakdown. The thermal stability of C₆₀H₃₆ was checked by a thermogravimetric analysis (TGA) coupled with a differential thermal analysis (DTA) under N₂ flow. The vaporization of C₆₀H₃₆ occurs at very high temperature: the DTA trace has shown an endothermic peak at 540°C (at a heating rate of 20°C/min). C₆₀H₃₆ shows an electronic absorption spectrum with a maximum at about 217 nm and it is able to match both in position and in half width the peak at 217.5 nm observed in the spectrum of the interstellar extinction of light which was attributed to hydrogenated, radiation processed and thermally annealed carbon dust. Similarly, the absorption spectrum of C₆₀H₃₆ is able to match several infrared emission bands (called UIBs) detected from certain astrophysical objects like the protoplanetary nebulae (PPNe). It is proposed that hydrogenated fullerenes can be used as model compounds in the laboratory simulation studies of interstellar carbon dust.     

Why are Solutions of C60-Piperazine Purple at pH 11?

The C₆₀-piperazine mono adduct was synthesized by the reaction of C₆₀ and piperazine. The saturated C₆₀-piperazine aqueous solution was colorless when pH is 8 or below. A purple color was developed when pH is around 9 and the pink color is most intense at pH 11. The color of the C₆₀-piperazine solution fades out when pH is approaching 12 from 11, and the solution remains colorless when pH is 13 or higher. The UV-Vis spectra of the C₆₀-piperazine solution were recorded at pH 4, 11 and 14. The mono-protonated C₆₀-piperazine was identified to be responsible for the purple color observed. The computational investigation of the un-protonated, mono-protonated and di-protonated C₆₀-piperazine was conducted at the PM3 and ZINDO(s) levels of theory. Vibronic coupling of the Jahn-Teller active vibrational mode to the electronic transition was applied to re-generate the weak absorption between 550-600 nm in the UV-Vis spectrum of the mono-protonated C₆₀-piperazine.     

The Solid-State Mechanochemical Reaction of Fullerene C60

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.     

Pyrolytic Trifluoromethylation of [76]-, [78]-, [84]-, and Aza[60]Fullerenes with Silver Trifluoroacetate; Evidence for Coordination of Fullerenes to Silver

Pyrolytic trifluoromethylation of [76], [78], [84], and aza[60]fullerenes with silver trifluoroacetate at 300°C results in extensive polyaddition of up to 18, 18, 20 and 20 CF₃ groups, respectively. In contrast to trifluoromethylation of [60]- and [70]fullerenes that give a full range of derivatives ranging upwards from C_n(CF₃)₂, [76]-, [78]-, and [84]-fullerenes only give C_n(CF₃)_6-18 derivatives, largely in the 10-12 CF₃ range; reaction with [76]fullerene is accompanied by formation of C₆₀(CF₃)₆ attributed to cage fragmentation. For aza[60]fullerene the hexa-addition level dominates, in contrast to its other reactions which give predominantly penta-addition products. All the compounds showed peaks at 1256±2 and 1180-1190 cm^-1, due to the CF₃ group, and peaks in this region are shown also by the soluble extract obtained on trifluoromethylation of nanotubes. As in trifluoromethylation of [60]- and [70]-fullerenes, the products obtained initially are involatile, attributed to formation os silver complexes; these are decomposed on subsequent solution in toluene. Mixed isomeric trifluoromethylated C₆₀F₈ derivatives viz. C₆₀F₇CF₃, C₆₀F₆(FG₃)₂, C₆₀F₅(CF₃)₃ and C₆₀F₄(CF₃)₄, and C₆₀F₄CF₃CF₂CF₃ (a C₆₀F₆ derivative) have been isolated from fluorination of [60]fullerene with MnF₃/K₂NilF₆ at 510°C.     

Spontaneous Decay of Highly-Charged Fullerene Ions C60Z and C58z

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.     

Preparation and characterization of C60S16 and C70S48 thin films

In this study, we have investigated different methods for preparation of thin films of C₆₀ and C₇₀-sulfur compounds. Films of good quality were obtained by reaction of amorphous C₆₀ and C₇₀ films with a saturated sulfur solution in toluene at 40°C or with saturated sulfur vapour at a temperature of 140°C for several hours. The quality of the fullerene-sulfur films were strongly dependent on the microstructure of the initially deposited fullerene film and the synthesis temperature. X-ray diffraction analyses showed that both methods lead to the formation of films consisting of C₆₀S₁₆ and C₇₀S₄₈ (space groups C 2/c and Amm2, respectively). C₆₀S₁₆ films synthesised on Al₂O₃(012) and Si(100) substrates were texture-free while C₇₀S₄₈ films typically exhibited a preferential (100) orientation. The films were also characterised by Raman and IR- spectroscopy, which confirmed that the interactions between the fullerene molecules and the S₈ rings are weak. The fullerene-sulfur compounds were found to be unstable at high vacuum conditions. Both materials C₆₀S₁₆ and C₇₀S₄₈ are non-conductive at room temperature with conductivities less then 10⁻⁵ (Ω/cm).     

Electronic Structure of C60, CuPc, and C60/CuPc Nanoparticles and their Layers

The idea to form C₆₀/CuPc dispersed nanoheterojunctions by photoexcitation of a mixture of C₆₀ and CuPc nanoparticles has been realized. The electronic structure of the nanoparticles and dispersed nanoheterojunctions formed in the mixture has been characterized by UV-Vis spectroscopy and the comparing with known experimental ultraviolet photoelectron spectra and theoretical models of electronic structure of these molecules. For the mixture of C₆₀ and CuPc nanoparticles in toluene and their coating layer on the quartz substrate the band offsets of the edges of CuPc VB and lowest unoccupied molecular orbital (LUMO) of C₆₀ band are ΔE=1.55 eV and 1.4 eV, respectively. These results show clearly the presence of C₆₀/CuPc dispersed nanoheterojunctions in the solution and on the quartz surface.     

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.     

Growth and Characterization of C60 Crystals from Pure C60 and Fullerite

Good quality C₆₀ crystals have been grown from high purity C₆₀ powder and fullerene mixture (C₆₀/C₇₀) by vacuum sublimation method. The grown crystals were characterized with Optical microscopy, SEM, powder XRD, High Performance Liquid Chromatography and Raman spectroscopic analyses.     

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.