Capture Of Non-Classical C₆₀ And Studies On Fullerene Formation Mechanism

Since the discovery of C₆₀ in 1985, the fullerenes obeying the isolated pentagon rule(IPR), such as C₆₀ and C₇₀, have been successfully synthesized and characterized, which awakes the wide investigations in basic and applied fields about the fullerenes. The synthesis, separation and characterization of non-IPR fullerenes, i.e. the fullerenes including adjacent pentagons, however, are still of great challenge.Meanwhile, there are many puzzles about the formation mechanism of fullernenes. Introducing the chlorine for the synthesis of the non-IPR fullerenes into plasma system is greatly significant for trapping these new species and in turn of importance for understanding of fullerene formation, as demonstrated by capturing labile C₅₀ as C₅₀Cl10. In this dissertation, the synthesis of fullernes under graphite arc discharged in the presence of chlorine and other halogens was systemically explored, and a series of experiments were carried out involving the capture of metastable intermediates of fullerenes, preparation of C₆₀ isomers chloride, as well as ¹³C-labeled formation mechanism investigation. The main results are summarized as follows.1. The conventional metal apparatuses for the synthesis of fullerenes are gradually mature in their synthesis mechanism and methods, but they somewhat suffer from leakage caused by the erosion of chlorine and other halogens. In order to improve these metal apparatuses, we design a corrosion-proof glass setup, and after 80 times experiments in a period of two years, the proposed equipment is still in good condition. Furthermore, the miniaturized glass apparatus is helpful for the quantification of reactants and products, as well as observation in situ.2. A small amount of chlorine mixed into helium atmosphere remarkably enhanced the yield of C₆₀ and C₇₀ in the graphite arc-discharge reaction, and especially in the atmosphere of 5 Torr chlorine and 300 Torr helium, the yield was promoted to more than a value of 6 folds compared with those without chlorine.Combining with other experimental results, we can predict that carbon clusters around 40 atoms probably prefer to cage structures rather than bowl shaped structures. The coordination effect between chlorine and helium contributes to the raised yield of fullerenes and is of significance for fullerenes synthesis on large scale, and provides valuable clues for the mechanism investigation of fullerenes formation.3. One isomer of C₆₀, in form of C₆₀C₁₈, has been synthesized by introducing chlorine to a graphite arc-discharge process. Analyses with single crystal diffraction, mass spectrum, ¹³C-NMR, infrared absorption, Raman, UV-Vis absorption and matrix-assisted laser desorption ionization time of flight mass spectroscopy, this octochlorofullerene[60] molecule has been characterized to be a quasi-spherical molecule with C2v symmetry which comprises two pairs of adjacent pentagons. It is expected that this species possesses some novel properties.4. The mass and UV-Vis absorption spectra of some chlorinated carbon clusters from C₂₀ to C₆₈ have been obtained. Among them the C₂₀ C₃₀ and C52 C₆₈ clusters are relatively abundant, the former may exist as bowl-shaped, and the latter clusters may adopt closed-cages, while the relatively rare C32 C48 clusters are still under the limitation of detection in our experiments. It can be suggested that the clusters may be the intermediates in the formation process of fullerenes and they are hard to be captured due to instability.5. The arc-dischrage experiments with ¹³C-label electrodes and gas atmosphere were performed to investigation of fullerene formation. We can conclude that C₆₀ and C₇₀ grow from C1 unit. The chlorinate carbon clusters of C6 C₂₀ formed in two different temperature zones. The group formed in high temperature zone was in relation with the formation of C₆₀ as well as other fullerenes, and the other group formed in relatively low temperature had nothing to do with fullerenes. That the hypothesis of C₆₀ and C₆₀C₁₈ sharing the same growth path was also confirmed in our experiments. Finally, the formation mechanism of fullerenes and other smaller carbon clusters in graphite arc system were investigated in this dissertation.