The hydrogenolysis of C60 and C70

Temperature-programmed reaction (TPR) of C₆₀ and C₇₀ with H₂ was carried out on nickel in order to investigate the thermal stability of the fullerenes in the catalytic hydrogenation. The TPR profiles showed two methanation peaks and the corresponding weight decrease above 420°C, indicating the hydrogenolysis to CH₄. This revised version was published online in June 2006 with corrections to the Cover Date.     

Semiempirical molecular dynamics studies of C60/C70 fullerene oxides: C60O, C60O2 and C70O

The spectral analysis indicates that all isomers of C₆₀O, C₇₀O and C₆₀O₂ have an epoxide-like structure (an oxygen atom bridging across a C–C bond). According to the geometrical structure analysis, there are two isomers of fullerene monoxide C₆₀O (the 5,6 bond and the 6,6 bond), eight isomers of fullerene monoxide C₇₀O and eight isomers of fullerene dioxide C₆₀O₂. In order to simulate the real reaction conditions at 300 K, the calculation of the different isomers of C₆₀O, C₆₀O₂ and C₇₀O fullerene oxides was carried out using the semiempirical molecular dynamics method with two different approaches: (a) consideration of the geometries and thermodynamic stabilities, and (b) consideration of the ozonolysis mechanism. According to the semiempirical molecular dynamic calculation analysis, the probable product of this ozonolysis reaction is C₆₀O with oxygen bridging over the 6–6 bond (C_2v). The most probable product in this reaction contains oxygen bridging across in the upper part of C₇₀ (6–6 bond in C₇₀O-2 or C₇₀O-4) an epoxide-like structure. C₆₀O₂-1, C₆₀O₂-3 and C₆₀O₂-5 are the most probable products for the fullerene dioxides. All of these reaction products are consistent with the experimental results. It is confirmed that the calculation results with the semiempirical molecular dynamics method are close to the experimental work. The semiempirical molecular dynamics method can offer both the reaction temperature effect by molecular dynamics and electronic structure, dipole moment by quantum chemistry calculation.     

Surface-enhanced raman spectra of C2H2 and C2H4 adsorbed on silver colloid

We report the surface-enhanced Raman spectra of ethylene and acetylene adsorbed on colloidal silver particles formed by gas aggregation and isolated at low temperatures in solid adsorbate/argon matrices. The spectra of both molecules exhibit modes which are normally Raman-forbidden. Excitation with several visible laser frequencies indicated that the degree of enhancement increased towards the blue.     

Molecular Complexes of Fullerenes C60 and C70 with Saturated Amines

New molecular complexes of fullerenes C₆₀ and C₇₀ with leuco crystal violet (LCV, 1-3); leucomalachite green (LMG, 4-6); crystal violet lactone (CVL, 7); N,N,N′,N′-tetrabenzyl-p-phenylenediamine (TBPDA, 8, and 9); N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPDA, 10, and 11); triphenylamine (TPA, 12, and 13); and substituted phenotellurazines (EPTA and TMPTA, 14, and 15) have been synthesized. Crystal structures have been solved for C₆₀ complexes with LMG (5, 6) TBPDA (8), TMPDA (10), and TPA (12). The C₆₀ molecules form closely packed double layers in 5 and 6, hexagonal layers in 10 and quasi-three-dimensional layers in 8 and 12. The substitution of disordered solvent molecules in the complexes with LMG (4, 5) by naphthalene ones results in the ordering of the C₆₀ molecules. According to IR-, UV-visible-NIR and ESR-spectroscopy the complexes have a neutral ground state. The spectra of 1-8, and 10 show intense charge transfer bands in the visible and NIR-range. On photoexcitation by white light (light-induced ESR (LESR) spectroscopy), 1 and 10 were shown to have an excited ionic state. The LESR signals were generated at light energies <2.25 eV indicating that the excited states in the complexes are realized mainly by direct charge transfer from donor to the C₆₀ molecule.     

Analysis of C60 and C70 fullerenes using high-performance liquid chromatography–Fourier transform infrared spectroscopy

The performance of Fourier transform infrared spectroscopy (FT-IR) detection coupled to high-performance liquid chromatography for the analysis of C₆₀ and C₇₀ fullerenes was investigated. The isocratic separation method involved an octadecylsilane (ODS) column and an acetonitrile–toluene (1:1) mobile phase. The hyphenated system was designed with a split valve to control eluent volume leading to the FT-IR detector; this allowed for additional coupling of the liquid chromatograph to ultraviolet–visible detection. On-line FT-IR spectra of C₆₀ and C₇₀ were matched with standard off-line FT-IR spectra from the literature. In addition, with band chromatograms individual fullerenes can be identified using FT-IR active modes known specifically for each fullerene. Few changes to a pre-existing HPLC–UV method were necessary for the HPLC–FT-IR method, and there was no need for fraction collection to identify the fullerenes C₆₀ and C₇₀.     

Comment on nuclear spin weights of C60 and C60 buckminsterfullerene

The nuclear spin statistical weights obtained in a Letter by Harter and Reimer differ from the values obtained by the author a year earlier. However, the corrected numbers reported in the Erratum by Harter and Reimer agree with our values.     

On the vibrational spectrum of C9, C11 and C13

The harmonic frequencies and infrared intensities of C₉, C₁₁ and C₁₃ have been calculated using SCF and complete active space SCF (CASSCF) methods. The ordering of the harmonic frequencies in C₉ is predicted wrongly unless at least the π HOMO and LUMO are included in the active space. Infrared intensities depend crucially on the size of the active space. For linear odd-numbered clusters C₁₃ and larger, the computed SCF spectrum is qualitatively wrong. The recent observation of a band near 1809 cm⁻¹ in the gas phase is explained using our CASSCF results on C₁₃.     

High-temperature and photochemical syntheses of C60 and C70 fullerene derivatives with linear perfluoroalkyl chains

New experimental results on perfluoroalkylation of C₆₀ and C₇₀ with the use of R_fI (R_f = CF₃, C₂F₅, n-C₃F₇, n-C₄F₉, and n-C₆F₁₃), along with a critical overview of the existing synthetic methods, are presented. For the selected new fullerene (R_f)_n compounds we report spectroscopic, electrochemical and structural data, including improved crystallographic data for the isomers of C₇₀(C₂F₅)₁₀ and C₆₀(C₂F₅)₁₀, and the first X-ray structural data for the dodecasubstituted perfluoethylated C₇₀ fullerene, C₇₀(C₂F₅)₁₂, which possesses unprecedented addition pattern.     

Effect of solvent polarity on the aggregation of fullerenes: a comparison between C60 and C70

Effect of solvent polarity on the aggregation behaviour of C₇₀ has been investigated in several mixed solvents using optical absorption, fluorescence, dynamic light scattering and scanning electron microscopic measurements and compared with those observed for the other fullerene analogue, C₆₀. It is seen that similar to C₆₀, aggregation of C₇₀ also requires the solvent polarity to exceed some critical value. In terms of solvent dielectric constant the critical solvent polarity, required for C₇₀ aggregation is found to be in the range of 27–31, which is much higher than that required for C₆₀ aggregation (12–14). The large difference in the critical solvent polarity required for C₆₀ and C₇₀ aggregation has been rationalized on the basis of the molecular shapes and the polarizabilities of two fullerene molecules.     

Stereochemical patterns in bromofullerenes C60Br2 to C60Br12

The stabilities of different isomers of C₆₀Br_n have been calculated for n = 2 to 12. A general stereochemical pattern which emerges is the tendency to form strings created by the edge sharing of C₆Br₂ hexagonal faces. Stable structures are formed if these strings form loops, thereby eliminating string ends, which may involve the creation of C₆Br₃ hexagonal faces. A particularly stable structure is formed at C₆₀Br₆ in which the loop forms a C₁₀Br₆ fragment with a pentagonal pyramidal arrangement of six bromine atoms. Two isomers of C₆₀Br₁₂ are also particularly stable. One isomer contains two of these Br₆ pentagonal pyramids on opposite sides of the molecule, and the other isomer contains a single large loop wrapped around the middle of the molecule.     

Radical scavenging efficiency of different fullerenes C60-C70 and fullerene soot

This investigation was undertaken to determine the antioxidant activity of a range of fullerenes C₆₀ and C₇₀ in order to rank them according to their comparative efficiency. The model reaction of initiated (2,2′- azobisisobutyronitrile, AIBN) cumene oxidation was used to determine rate constants for addition of radicals to fullerenes. Measurements of oxidation rates in the presence of different fullerenes showed that the antioxidant activity as well as the mechanism and mode of inhibition were different for fullerenes C₆₀ and C₇₀ and fullerene soot. All fullerenes - C₆₀ of gold grade, C₆₀/C₇₀ (93/7, mix 1), C₆₀/C₇₀ (80 ± 5/20 ± 5, mix 2) and C₇₀ operated as alkyl radical acceptora, whereas fullerene soot surprisingly retarded the model reaction by a dual mode similar to that for the fullerenes and with an induction period like many of the sterically hindered phenolic and amine antioxidants. For the C₆₀ and C₇₀ the oxidation rates were found to depend linearly on the reciprocal square root of the concentration over a sufficiently wide range thereby fitting the mechanism for the addition of cumylalkyl radicals to the fullerene core. This is consistent with literature data on the more ready and rapid addition of alkyl and alkoxy radicals to the fullerenes compared with peroxy radicals. Rate constants for the addition of cumyl radicals to the fullerenes were determined to be k_(333K) = (1.9 ± 0.2) × 10⁸ (C₆₀); (2.3 ± 0.2) × 10⁸ (C₆₀/C₇₀, mix 1); (2.7 ± 0.2) × 10⁸ (C₆₀/C₇₀, mix 2); (3.0 ± 0.3) × 10⁸ (C₇₀), M⁻¹ s⁻¹. The increasing C₇₀ constituent in the fullerenes leads to a corresponding increase in the rate constant.The fullerene soot inhibits the model reaction according to the mechanism of trapping of peroxy radicals; the oxidation proceeds with a pronounced induction period and kinetic curves are linear in semi-logarithmic coordinates.For the first time the effective concentration of inhibiting centres and inhibition rate constants for the fullerene soot have been determined to be fn[C₆₀−soot] = (2.0 ± 0.1) × 10⁻⁴ mol g⁻¹ and k_inh = (6.5 ± 1.5) × 10³ M⁻¹ s⁻¹ respectively.The kinetic data obtained specify the level of antioxidant activity for the commercial fullerenes and scope for their rational use in different composites. The results may be helpful for designing an optimal profile of composites containing fullerenes.     

Non-covalent immobilization of C60 on gold surfaces by SAMs of porphyrin derivatives

Three porphyrin derivatives, one containing thioctic ester groups (3) and the other two with thioether chains (4 and 5), were synthesized. The cyclic voltammograms of the porphyrin compounds exhibit two reversible reduction processes and one reversible oxidation. Stable self-assembled monolayers (SAMs) of the porphyrin compounds were formed on gold surfaces. Non-covalent immobilization of C₆₀ was accomplished upon incubation of some of the porphyrin SAMs in solutions of C₆₀.     

Surface-enhanced Raman spectroscopy using silver nanoparticles on a precoated microscope slide

A chemical reduction method was applied to deposit nano silver particles on a frosted microscope slide, precoated with indium tin oxide. The substrate was used to collect the surface-enhanced Raman spectrum of N1'-ethyl indirubin monooxime (EIM), a potential chemical for pharmaceutical application. From the observed surface-enhanced Raman scattering (SERS) spectrum, EIM might interact with silver surface through the lone pair electrons of the oxime nitrogen atoms. Crystal violet (CV) and p-nitrobenzoic acid (PNBA) were also used to test the SERS probe capability of the substrate. The surface morphorlogy of the substrate has been characterized by using scanning electron microscope (SEM) and atomic force microscope (AFM). The elementary composition was identified with Edex and X-ray element scanning.     

Surface-enhanced Raman spectroscopy of dodecanethiol-bound silver nanoparticles at the liquid/liquid interface

Adsorption and domain formation of dodecanethiol (DT)-bound silver nanoparticles (SNPs) at the cyclohexane/water interface were studied by means of total internal reflection (TIR) light scattering microscopy and TIR surface-enhanced Raman scattering (SERS). By the TIR light scattering microscopy, the extent of the interfacial adsorption and domain formation of SNP was observed, which was produced by the reaction between citrate-reduced SNPs in the aqueous phase and DT in the cyclohexane phase. The Raman spectra of DT on SNP showed that the relative intensity ratios of gauche to trans conformers in the nu(C-S) band region decreased with the increase of the initial concentration of DT, suggesting the change from the liquidlike structure to the solidlike structure of the DT. The residue of the negative charges on the SNPs at the interface was detected by the resonance SERS (SERRS) peaks of the adsorbed cationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine (TMPyP). The efficiency of the interfacial SNPs domains as a SERS substrate for TMPyP strongly depended on the adsorption state of the DT.     

C60的氧化反应研究

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Surface-enhanced Raman spectroscopy of 12CN− and 13CN− adsorbed at silver electrodes

Measurements are reported of the surface-enhanced Raman of ¹²CN and ¹³CN (and of isotopically labelled mixtures) adsorbed at silver electrodes. The spectra are shown to arise from a complex species whose coordination number does not change with electrode potential. This species is probably a [Ag(CN₂)]^? entity having C_2v symmetry; at very negative potentials a reduced form of this complex [Ag(CN)₂]^2? coexists with the formally Ag¹ species at the surface. The shifts in band position are interpreted in terms of changes in the bond character of the adsorbed CN^? species. The spectrum of water coadsorbed with CN^? is also markedly dependent on the charge density of the adsorbed CN^? groups.     

Synthesis and molecular structures of heptafluoropropylated fullerenes: C70(n-C3F7)8, C70(n-C3F7)6O, and C70(C3F7)4

Ampoule reactions of C₇₀ with n- and i-C₃F₇I were carried out at 250-310 °C. Two step HPLC separations allowed the isolation of several C₇₀(n-C₃F₇)_4-8 and C₇₀(i-C₃F₇)₄ compounds. Crystal and molecular structures of C₇₀(n-C₃F₇)₈-V, C₇₀(n-C₃F₇)₆O, C₇₀(n-C₃F₇)₄, and three isomers of C₇₀(i-C₃F₇)₄ have been determined by X-ray crystallography using synchrotron radiation. Molecular structures of the new compounds were compared with the known examples and discussed in terms of addition patterns and relative energies of their formation.     

C60的加成反应

富勒烯化学是以全碳分子球烯为母体的新兴有机化学领域, 在材料、医学及立体化学合成方法等方面具有广泛的应用和发展前景。本文综述了C₆₀的加成反应, 较全面地展示了富勒烯的化学性质。     

Catalytic hydrogenation of C60 fullerene

Catalytic hydrogenation of C₆₀ with H₂ or by hydrogen transfer reactions using Pd/SiO₂, Rh/Al₂O₃ and Ru/Al₂O₃ has been studied. The final products containing partially hydrogenated C₆₀ fullerence C₆₀H₄₂–C₆₀H₄₆ were characterized by FTIR, UV and NMR methods.