Thermodynamic Properties and Hydrogen Accumulation Ability of Fullerene Hydride C60H36

Thermodynamic properties of fullerene hydride C₆₀H₃₆ in the ideal-gas and crystal states were studied by theoretical methods. Molecular structures and vibration frequencies were calculated for 9 isomers of C₆₀H₃₆ by the density functional theory (DFT) by use of a combination of the B3LYP functional with 6-31G* basis sets. Ideal-gas thermodynamic properties were calculated based on those parameters. Enthalpies of formation of C₆₀H₃₆ isomers in the ideal-gas state were derived from homodesmic reactions involving adamantane, cyclohexane, and C₆₀ fullerene. Using the standard methods of statistical mechanics, heat capacity and derived thermodynamic properties of crystalline C₆₀H₃₆ were calculated at 340-1000 K that extended the range of experimental measurements. With a crystal-gas heat capacity difference, the experimental value of sublimation enthalpy was extrapolated to room temperature as Δ_subH_m^o (298.15 K)=(193±10) kJ · mol^-1. Combining this value with the known experimental enthalpy of formation in the crystalline state, the ideal-gas enthalpy of formation of C₆₀H₃₆ at the synthesized sample isomer composition was obtained: Δ_f H_m^o (298.15 K)=(1206±28) kJ · mol^-1. Equilibrium constants and compositions were calculated for the reactions of hydrogenation of C₆₀ fullerene in different states. It was shown that C₆₀ can act as a hydrogen accumulator.     

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.     

Solubility of Fullerenes C60 and C70 in Seven Normal Alcohols and Their Deduced Solubility in Water

The solubilities of C₆₀ and C₇₀ at 25°C in seven normal alcohols obey the relationship InY = a + bX + cX², where Y is solubility and X is the Hildebrand solubility parameter of the solvent. Extrapolation to the solubility parameter of water yields solubilities in water of 1.3'10^-11 (C₆₀) and 1.3'10^-10(C₇₀) ng/ml with an uncertainty of one order of magnitude.     

On the Evaporation of C60 in Vacuum and Inert Gases at Temperatures Between 830 K and 1050 K

The binary diffusion coefficient D_AB of subliming C₆₀ in He, N₂ and Ar gas has been determined at a gas pressure between 5 and 10 kPa. It resulted D_AB/(cm^2/s)=D_o(P_o/P_t(T/T_o)ⁿ as a function of the total pressure P_t of the vapor phase and temperature T. At T_o=273 K and P_o=1.0133×10⁵ P_a, the values D_o = (0.059±0.004) cm²/s, (0.011±0.003) cm²/s, (0.012±0.007) cm²/s, n = 1.77±0.06, 2.02±0.18, 1.77±0.37 were obtained for He, N₂, Ar and (830-1000) K, (800-1020) K, (875-1095) K, respectively. Only 40 wt% of the initial C₆₀ material yielded reliable D_AB where the vapor pressure of C₆₀ followed log₁₀(P/Pa) = -(8976±60)/T/K+(11.05±0.07) for T between 640 and 1055 K.     

Reaction Kinetics of C60 Fullerene Ozonation

It has been verified that the reaction between O₃ and C₆₀ follows the general second order reaction rate which is valid for all the reactions between ozone and unsaturated olefinic bonds: v = k[C=C][O₃]. The reaction rate constant k has been measured ≈(1.5 ± 0.3) × 10⁴ L mol^-1 s^-1. The value of this rate constant has the same order of magnitude of the rate constant measured for instance in the ozonation of 1,4-diphenylbutadiene.     

C1 C60F16O: A Fluorofullerene Ether Having Exceptionally Long Chromatographic Retention

From the product of fluorination of [60]fullerene with K₂PtF₆ at 470 °C, we have isolated a small quantity (ca. 0.5 mg) of C₆₀F₁₆O, an oxahomofluorofullerene (ether) of exceptionally long HPLC retention time (50% greater than any other known fluorofullerene). The ¹⁹F NMR spectrum consists of 16 main lines and 8 minor ones, due to C₆₀F₁₆O (a single isomer of C₁ symmetry) and C₆₀F₁₆, respectively. The presence of the latter (absent on initial isolation) indicates this ether to be relatively unstable, confirmed by the failure to obtain an EI mass spectrum. The empirical formula was therefore determined by MALDI-TOF mass spectrometry in the negative-ion mode, the laser fluence being carefully adjusted at the threshold of ion formation, whence the only observable signal corresponded to the molecular ion of C₆₀F₁₆O. At slightly higher laser fluence, the base peak of C₆₀F₁₆O^·- is accompanied by C₆₀F₁₆^·- and C₆₀F₁₅O^·-. Two closely similar structures (of similar calculated stabilities) are fully consistent with the NMR data. Calculated dipole moments and the exceptionally long retention HPLC retention times suggest that both C₆₀F₁₆ and C₆₀F₁₆O may be dimers.     

RADIATION CHEMICAL AND PHOTOPHYSICAL PROPERTIES OF C60(C4H8SO3Na)n IN AQUEOUS SOLUTION: A LASER FLASH PHOTOLYSIS AND PULSE RADIOLYSIS STUDY

Optical absorption studies on aqueous solutions of C₆₀(C₄H₈SO₃Na)_n (n = 4-6) revealed deviation from the Beer-Lambert law in the 250-350 nm region, which is assigned to the formation of solute aggregates at concentrations higher than 1 × 10^-3 mol dm^-3. Dynamic light scattering experiments showed aggregates with an average size of ∼100 nm. The solute has a broad weak fluorescence emission (ϕ_f = 1.8 × 10^-3) in the 450-650 nm region, which remained independent of solute concentration. The broad transient absorption band in the 450-900 nm region (ε₆₆₀ = 2170 dm³ mol^-1 cm^-1), which formed immediately on laser flash photolysis (λ_ex = 355 nm, 35 ps), is assigned to singlet-singlet transition. It decays to a triplet excited state whose absorption is observed to depend strongly on solute concentration. In dilute solutions, an absorption band with λ_max = 590 nm is seen, and at high solute concentration a broad absorption in the 500-900 nm region is observed. The e_aq^- reacts with the solute with a bimolecular rate constant of 1.7 × 10⁸ dm³ mol^-1 s^-1 and forms weak broad absorption bands at 440, 540, 620, 870, 940, and 1020 nm. Isopropanol radicals also react with the solute with a bimolecular rate constant of 2.3 × 10⁸ dm³ mol^-1 s^-1 with the formation of a transient optical absorption spectrum similar to that observed on reaction with e_aq^- and assigned to a solute radical anion. The ^•H and ^-OH radicals react with bimolecular rate constants of 3.2 × 10⁹ and 4.4 × 10⁹ dm³ mol^-1 s^-1, respectively, and form transient absorption bands at 440, 510, and 660 nm. Based on electron transfer studies with suitable electron donor/acceptor substrates, the ranges of the reduction and oxidation potentials of the solute an estimated.     

Spectral Properties of Single Crystals of the 2:1 Product of C60 and Tetrathiotetracene

Reaction of C₆₀ with tetrathiotetracene (TTT) gives an adduct of formula (C₆₀)₂ · TTT · 0.5CS₂. The single crystals and powdered samples of the TTT and (C₆₀)₂ · TTT · 0.5CS₂ have been spectroscopically characterized. It was shown that the transmission spectra of the adduct contain not only the IR active modes of the components but also numerous features arising from isotopic or solid-state effects due to the symmetry breaking of the C₆₀ molecules.     

Laser Photolysis Study on Mechanism and Efficiency of Electron Transfer Between Fullerenes (C60 and C70) and Tetraselenafulvalenes

Efficient electron-transfer reactions from three kind of tetraselenafulvalenes (TSeF's) to photoexcited triplet state of C₆₀ or C₇₀ in polar solvents have been confirmed by transient absorption spectroscopy observing the decay of ³C₆₀*/³C₇₀* and rise of C₆₀^-•/C₇₀^-•. Growth of single crystal seems to be stimulated by laser irradiation of the solution containing C₆₀ and bis(ethylenedithio)tetraselena-fulvalene (BEDT-TSeF), in which C₆₀^-• was effectively formed.     

Liquid-Liquid Extraction, Separation, Preconcentration, and ICP-AES Determination of Lanthanum and Cerium with N-Phenyl-(1,2-methanofullerene C60)61-formohydroxamic Acid

A novel method for liquid-liquid extraction, separation, preconcentration, and simultaneous trace determination of cerium(IV) and lanthanum(III) with N-phenyl-(1,2-methanofullerene C₆₀)61-formohydroxamic acid (PMFFA) is reported. Lanthanum and cerium are extracted at pH 8.5 and 9.5, respectively in chloroform and recovered from monazite sands in the presence of thorium, uranium, and large number of cations and anions in high purity (99.98%). The extraction mechanism is investigated. The influence of PMFFA, pH, diverse ions, and temperature on the distribution constants of lanthanum and cerium was examined. The overall stability constants (log β₂K_e) and extraction constants (K_ex) for lanthanum(III) are 22.50 and 5.0 × 10^-9, respectively and for cerium(IV) are 21.51 and 3.9 × 10^-9, respectively. Lanthanum(III) gives a colourless complex with PMFFA which is extracted into chloroform having molar absorptivity 5.5 × 10⁴ L mol^-1 cm^-1 at 395 nm, and Beer's law 0.12-2.52 µg mL^-1, while cerium(IV) forms a red coloured complex, λ_max 460 nm, molar absorptivity 1.5 × 10⁴ L mol^-1 cm^-1, and Beer's law 0.46-9.26 µg mL^-1. For trace determination the extracts were directly inserted into the plasma for inductively coupled plasma atomic emission spectrometry ICP-AES measurements of lanthanum and cerium which increases the sensitivity 60 folds and obey Beer's law in the range, 2.1-37.5 ng mL^-1 for lanthanum and 9.2-186.4 ng mL^-1 for cerium. The method is applied for the determination of lanthanum and cerium in real and standard samples, sea water, and environmental samples.     

Spectroscopic Evidence for Anionic Coordination Complexes of the Transition Metals with C70 and the Higher Fullerenes C76, C78, C82, C84, C86, C90, and C92

The carbonylate anions [M(CO)₅]^- (M = Mn, Re), [Co(CO)₄]^-, [CpFe(CO)₂]^-, and [CpM(CO)₃]^- (M = Mo, W) react with C₇₀ via single electron transfer processes to give, respectively, the corresponding 17-electron, metal-centered radicals Co(CO)₄, M(CO)₅ (M = Mn, Re), CpFe(CO)₂, and CpM(CO)₃ (M = Mo, W) in addition to the radical anion C₇₀^-. In secondary thermal or photochemical processes, the metal-centered radicals Co(CO)₄ and M(CO)₅ (M = Mn, Re) combine with the C₇₀^- to form the new η²-C₇₀ complexes [Co(CO)₃(η²-C₇₀)]^- and [M(CO)₄(η²-C₇₀)]^-. However, the metal-centered radicals CpM(CO)₃ (M = Mo, W) require photolysis to react with C₇₀^- to form [CpM(CO)₂(η²-C₇₀)]^-, whereas neither thermolysis nor photolysis induces reaction between CpFe(CO)₂ and C₇₀^-. The photochemical reaction of [Mn(CO)₅]^- with a mixture of higher fullerenes known to contain at least C₇₆, C₇₈, C₈₄, C₈₆, and C₉₀ resulted similarly in the formation of the higher fullerene complexes [Mn(CO)₄(η²-C_n)]^- (n = 76, 78, 80, 82, 84, 86, 88, 90, 92, 96, and 98), all identified using electrospray mass spectrometry.     

Solubility of Fullerene C60 and C70 in Toluene, o-Xylene and Carbon Disulfide at Various Temperatures

The solubilities of fullerene C₆₀ and C₇₀ in toluene, o-xylene and carbon disulfide between the melting point and boiling point of the solvents, respectively, have been measured. The temperature dependent solubility of C₆₀ displays anomalous behaviors. A solubility maximum of C₆₀ around 0 °C for toluene and carbon sulfide and around 30 °C for o-xylene was observed. The temperature-dependent solubility of C₇₀ behaves normally for all the three solvents studied.     

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).     

Thermolysis and Photolysis of C60 Diozonides

Ozonation of C₆₀ in o-xylene produced three C₆₀(O₃)₂ diozonides that were separated from one another and from two C₆₀(O₃)₃ triozonides by High Performance Liquid Chromatography (HPLC). Upon thermolysis at 10, 15, and 16.6°C, each of the diozonides dissociated sequentially, first to a C₆₀O(O₃) oxyozonide, then to a C₆₀O₂ diepoxide. The three diepoxides were stable in solution for at least 3 weeks. The mean lifetimes of the three diozonides were 52 ± 5, 62 ± 6, and 17.3 ± 1.8 min, respectively (all at 15°C). The mean lifetimes of the three oxyozonides were 69.7 ± 0.7 and 58 ± 6 min at 16.6°C, respectively and about 240 min at 10°C. Photolysis of the diozonides yielded two dioxidoannulenes with UV-Vis adsorption maxima at 333 and 332 nm, and what appeared to be an epoxide-oxidoannulene with UV-Vis adsorption maximum at 327 nm. These annulenes were observed to form dimers. We have synthesized and characterized six C₆₀O₂ dioxides, at least three and possibly four of which were hitherto unknown. We report the discovery of oxyozonides that form during the dissociation of diozonides.     

Effects of Hexasulfobutylated C60 on the Thalamic Neurons in Neonatal Rat in vitro

The effects of hexasulfobutylated C₆₀ (FC₄S) on membrane potentials and currents were studied by tight-seal, whole-cell recording in thin slices of the neonatal rat thalamus. Silent neuron with resting membrane potentials of around -62.4 ± 0.7 mV was found in whole-cell current clamp recordings. Hexasulfobutylated C₆₀ depolarized the neuron by a concentration dependent manner. It also (1) prolonged the decay time constant of action potential and (2) decreased the threshold of the directly elicited action potentials of the neuron. Hexasulfobutylated C₆₀ did not alter the input resistance of the excitable membrane. In whole-cell voltage clamp studies, depolarizing command pulses from a holding potential of about -70 mV evoked a fast inward current followed by an outward current in the thalamic neurons. Hexasulfobutylated C₆₀ (30 - 100 μM) increased the total inward sodium current of the neuron, while hexasulfobutylated C₆₀ did not alter the outward potassium currents in all voltage steps tested. It was concluded that hexasulfobutylated C₆₀ (1) decreased the threshold of the action potential and (2) prolonged the decay time constant of the directly elicited action potential of the neonatal rat thalamic neurons. The effect may be closely associated with the Na⁺ current in thalamic neurons.     

INHIBITORY EFFECTS OF FULLERENE C60 DERIVATIVES ON ENDOTHELIUM-DERIVED RELAXATION IN RABBIT THORACIC AORTA

Inhibitory effects of newly synthesized fullerene C₆₀ derivatives 1 (C₆₀-bis(N,N-dimethylpyrrolidinium iodide)), 2 (C₆₀-proline-N-acetic acid) and 3 (C₆₀-ethylenediamine-N, N'-diacetic acid) on acetylcholine-induced relaxation in endothelium-intact rabbit thoracic aorta precontracted by phenylephrine (10^-6 M) were studied. Fullerene C₆₀ derivative 1 (3 × 10^-6 M), 2 (10^-5 M) and 3 (10^-5 M) reduced the maximum amplitude of the acetylcholine-induced relaxation without significantly changing the pD₂ values obtained from the concentration - response curves. In the presence of fullerene C₆₀ derivative 1 (10^-5 M) the acetylcholine-induced relaxation was eliminated and an acetylcholine-induced contraction was observed. These results suggest that fullerene C₆₀ derivative 1 strongly inhibits endothelium (nitric oxide)-dependent acetylcholine-induced relaxation in thoracic aorta of rabbit.     

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.     

Transport Property of C60 and C70 Single Crystals

Since a few years ago, many studies have been carried out for C₆₀ single crystals in the interest of superconductivity¹⁾ and other physical and chemical properties as a new device material. Recently, such related properties have been also interested for C₇₀ single crystals. In order to clarify the mechanism of superconductivity of C₆₀ or to discover the superconductivity of C₇₀, it is necessary to investigate the fundamental transport properties of the non-doped single crystal. In this work, to compare those transport properties of non-doped C₆₀ and C₇₀ single crystals, temperature dependence of the resistance was measured for the both single crystals prepared by a sublimation method. Each activation energy for C₆₀ or C₇₀ at high temperature was determined and phase transition temperatures for the both were discussed.     

A Study of Fullerene Preparation Technique

A new homemade are fullerene generator used in this experiment is reported. The comparation of yields of fullerenes (C₆₀/C₇₀ mixture) was studied by different power supplies (AC and DC), different gaps of two graphite rods and different He pressure between 0.4×10⁴- 2.8×10⁴ Pa. In our experiment, the highest yield up to 13% was achieved, when DC discharge was used and the optimum He pressure was near 0.8×10⁴ - 1.6×10⁴ Pa.

The mixed fullerene was analyzed by electron impact masa spectnun (EIMS). The relative amount af C₆₀ to C₇₀ was 4.2 to 1. After column chromatography aeperation with hexane on alumina, 99.9% Cso was obtained. FTIR and ^1aC-NMR epectrum were ueed to characterize the pure C₆₀ samples.     

An Invariant of Carbon Arc Synthesis of Fullerenes

The yields of fullerenes C₆₀ and C₇₀ were determined in a wide range of controlled parameters. The total yield of fullerenes varied from 3 to 24%. The molar relative contents C₆₀/C₇₀ appeared to be constant for all samples of toluene extracts of the soot and equal to 5.06 ± 0.1. The accuracy of this constancy (± 2%) was determined by application of a special mathematical processing to the spectra of toluene extracts.