Thermochemistry of C60 and C70 fullerene solvates

In an effort to improve understanding of dissolution behaviour of fullerenes and their simple chemical derivatives the binary systems of C₆₀, C₇₀ and the piperazine monoadduct of [60] fullerene C₆₀ N₂C₄H₈ with a series of aromatic solvents have been studied by means of DSC. In certain systems solid solvates have been found to be the thermodynamically stable phases relative to saturated solution at room temperature. Identified solid solvates were characterized by their compositions, temperatures and enthalpies of incongruent melting transitions. The regularities in thermodynamic stability of the solvated crystals have been discussed along with dissolution properties of fullerenes and the derivative. Certain correlations have been observed.     

C60-C70-C6H5CH3 crystal solvates: Structure and thermal stability

Differential scanning calorimetry (DSC) and X-ray diffraction were used to study the thermal stability and structure of C₆₀-C₇₀-C₆H₅CH₃ crystal solvates synthesized at room temperature. The decomposition of the crystal solvates generates C₆₀-C₇₀ solid solutions with hexagonal close-packed (hcp) structure.     

IR-Fourier spectroscopic studies of structural changes in fullerenes C60 and C70-Toluene systems

The C₆₀-toluene and C₇₀-toluene complexes were studied by IR-Fourier spectroscopy. The complexes were obtained by crystallization from a toluene solution at room temperature. The changes in the IR spectra caused by the deformation of toluene molecules in the complexes allowed us to study the phase transitions in the fullerene-aromatic solvent systems.     

Theoretical studies of C60/C70 fullerene derivatives: C60O and C70O

A semiempirical (AM1) calculation on the structures and stabilities of isomers of the fullerene derivatives C₆₀O and C₇₀O is carried out. The ozonolysis reaction mechanism and the thermodynamics of the compounds are studied. The two isomers of C₆₀O (56 bond and 66 bond) formed by an oxygen atom bridging across a C-C bond have an epoxide-like or an annulene-like structure. According to the ozonolysis reaction mechanism and kinetic factor analysis, the possible products of this ozonolysis reaction are C₆₀O with oxygen bridging over the 66 bond (C_2v) as an epoxide-like isomer and that with oxygen bridging over the 56 bond (C_s) as an annulene-like isomer. Further, the sixteen isomers of C₇₀O (both epoxide-like and annulene-like structures) have been studied with respect to the same reaction mechanism. The most possible product in this ozonolysis reaction contains oxygen bridging across in the upper part (66 bond in C₇₀O-2 or C₇₀O-4) as an epoxide-like structure. The other possible product is C₇₀O-8 (annulene-like structure), in which oxygen bridges across an broken equatorial CC bond in C₇₀ (D_5h). The vibrational frequency analysis and the electronic structure of the selected C₆₀O and C₇₀O isomers are generated for experimental characterisation. The experimental results indicate that C₆₀O and C₇₀O may decompose into the odd number fullerenes C₅₉ and C₆₉. We therefore studied the structures of C₅₉ and C₆₉ also.     

Oxidation of C60 and C70 fullerites in air

The oxidation of C₆₀ and C₇₀ fullerites and C₆₀/C₇₀ mixture is accompanied by the decomposition of the carbon frameworks of the molecules at annealing temperatures of 250 and 445°C. Fourier-IR and HPLC studies show that the oxidation/decomposition of C₇₀ molecules is more active than that of C₆₀. The stages of fullerite interaction with oxygen while heating in air were determined.     

Rydberg electron transfer to C60 and C70

Experimental results are reported for the attachment of Ar* * (nl) Rydberg electrons to C₆₀ and C₇₀ over the range n = 19–270. In agreement with other Rydberg work we find that the rate coefficient for C ₆₀ ^? formation remains large (around 2·10^-8 cm³ s^-1) towards high n and is essentially constant for n > 40, thereby indicating the presence of an s-wave attachment process in contrast to interpretations of free electron attachment data postulating p-wave threshold behaviour. The rate coefficients for C ₇₀ ^? formation show a similar n-dependence as those for C ₆₀ ^? , but they are significantly larger. Possible mechanisms for s-wave attachment including formation of polarization-bound negative ion states are discussed. Regarding the threshold behaviour for the attachment of free electrons to C₆₀ we propose — based on an analysis of available free electron data — the presence of an s-wave (possibly resonance type) contribution near zero energy.     

Distribution of C60 and C70 fullerenes in the extraction system (C60 + C70)-α-pinene-ethanol-H2O

The distribution of C₆₀ and C₇₀ fullerenes in the extraction system (C₆₀ + C₇₀)-α-pinene-ethanol-H₂O was studied at constant C₆₀ to C₇₀ ratio and variable total fullerene concentration at 25°C. The relationship between the C₆₀ and C₇₀ content in ethanol (I) and α-pinene (II) phases is nonlinear over the entire fullerene concentration range.     

富勒烯C60、C70的超分子化学

介绍了富勒烯Ｃ６０、Ｃ７０与环糊精、冠醚、杯芳烃等主体形成超分子的进展和一些潜在的应用前景。     

The vibrational Raman spectra of C60 and C70

Vibrational Raman spectra have been obtained at 1 cm⁻¹ resolution, for C₆₀ and C₇₀. For C₆₀ the positions of the bands were in good agreement with theoretical predictions. For C₇₀ 27 bands were observed out of the total of 53 that were theoretically predicted. These data will permit refinement of calculations of vibrational lines appropriate to closed-cage carbon clusters. The technique for producing appreciable quantities of high purity C₇₀ is described.     

活性碳分离碳—60和碳—70

活性碳用苯胺处理后，可以减少对Ｃ６０和Ｃ７０的不可逆吸附，从而增加Ｃ６０和Ｃ７０的分离收率，同时提高了Ｃ７０的纯度。     

Semiempirical vibrational and electronic structures of C60 and C70

The electronic and vibrational structures of C₆₀ and C₇₀ have been calculated at the PM3 semiempirical level. C₆₀ has a partially delocalized structure, while C₇₀ has both a localized set and a delocalized set of MOs. As with AM1 and MNDO, PM3 predicts the heat of formation of C₇₀ to be greater than that of C₆₀, and that C₇₀ is the thermodynamically more stable species. Calculation of the normal modes was accelerated over 40 times by limited use of symmetry theory.     

Synthesis and structural characterization of highly chlorinated C70, C70Cl28

Chlorination of [70]fullerene with SbCl(5), VCl(4) or PCl(5) yielded C(70)Cl(28) comprising three isomers, all containing four isolated benzenoid rings in the fullerene cage. This demonstrates, for the first time for C(70) derivatives, a stabilization effect due to planar aromaticity.     

浅谈富勒烯C60、C70发现的偶然性与必然性

1985年英国萨塞克斯大学(University of Sussex)的波谱学家H.W.Kroto与美国莱斯大学(Rice University)两名教授R.E.Smalley和R.F.Curl合作研究,发现碳元素可以形成由60个或70个碳原子构成的有笼状结构的C60和C70分子[1],这一发现引起科学界特别是物理学和化学界的强烈反响,成为本世纪后半叶的重大科学发现之一.11年后,三位科学家因为发现C60并提出其分子结构模型而荣获1996年诺贝尔化学奖.回顾C60的发现过程,应当承认,确有偶然性的一面,但从人类的认识规律和科学技术发展背景分析,C60的发现又有着历史的必然性.     

Microscopic structure of collective density oscillations C60 and C70

The microscopic structure of the photo-excited plasmon excitation in C₆₀ and C₇₀ is investigated using linear response theory. One finds that Landau damping provides the main contribution to the lineshape and the linewidth of the Mie-type plasmon being able, in the case of C₇₀, to mask the deformation splitting effect associated with the low equilibrium symmetry (D_5h) of this fullerene. Furthermore, it is found that the coupling of the plasmon to the normal modes of vibration of the fullerenes provides a sizeable contribution to the lineshape, without significantly affecting the linewidth. This coupling is found to be active already atT=0, exhibiting a weak temperature dependence.We would like to dedicate this work to Michael Hansen, who actively participated in most of the work and studies carried out in this paper, and who is not among us anymore     

The electrochemical reduction of fullerenes, C60 and C70

The hexaanion of fullerene, C(60)(6-), was obtained in 1:5 (v/v) acetonitrile-toluene mixture with a mercury hemispherical ultramicroelectrode as a working electrode at a temperature of up to 30 degrees C. The C(70)(6-) ion also can be observed under the same conditions. The differences between the redox potentials of C(60) relative to C(70) indicate that it is easier to add electrons to C(70) and its anions compared to the counterparts of C(60). The results show that the mercury electrode is very suitable for investigation of the properties of the electrochemical reduction for the fullerenes, particularly C(60), at room temperature.     

Inclusion properties of 3-fluoromesotetraphenylporphyrin with C60 and C70

To improve the selectivity ratio of C70 over C60, a new designer molecule, viz., 3-fluoromesotetraphenylporphyrin (1) has been reported in the present investigations. Fluorescence studies reveal that the Q-absorption band of 1 gets sufficient quenching effect upon addition of both C60 and C70. Binding constants (K) of the C60/1 and C70/1 complexes are estimated to be 580 and 10,800 dm3 mol(-1), respectively. Thus, K(C70)/K(C60) is approximately 19 which is very large and even comparable with other macrocyclic host molecules like calix[5]arene, azacalix[m]arene[n]pyridine, cyclotriveratrylenophane and calixarene bisporphyrin. 1H NMR chemical shift measurements show that the -NH- proton of 1 suffers more shifts in presence of C70 compared to C60. This finding also offers a good support in favor of high K value for C70/1 complex as well as large selectivity ratio of C70 over C60.