Fullerenes separation

Intense efforts in the last decade have exhaustively mapped the electronic and superconducting properties of intercalated alkali fullerides and the occurrence of the metal-antiferromagnetic insulator transition as a function of inter -fullerene separation, orientational order/disorder, valence state, orbital degeneracy, low-symmetry distortions and metal-C60 interactions [6-12]. 

Fullerene separations have been studied extensively [269]. Due to their high molecular weights and nonpolar character, the alkanes and alkylbenzenes have been widely used as the solvents of choice. C o and C70 fullerenes were resolved on a dinitroanilinepropyl column (A = 380 nm) using either a 30/70 dichloromethane/ hexane or a 50/50 hexane/benzene mobile phase [652]. Solutions containing 1 mg/mL of sample were prepared and 5 pL injections were made. The authors note that ethyl ether/hexane solvents generated broad asymmetric peaks most likely due to the precipitation of the sample. 

An example of the application of HPLC is the separation of fullerenes (see Section 14.4). Columns packed with stationary phases designed specifically for preparative-scale fullerene separation are commercially available (e.g. CosmosiF Buckyprep columns). 

One aspect that reflects the electronic configuration of fullerenes relates to the electrochemically induced reduction and oxidation processes in solution. In good agreement with the tlireefold degenerate LUMO, the redox chemistry of [60]fullerene, investigated primarily with cyclic voltammetry and Osteryoung square wave voltammetry, unravels six reversible, one-electron reduction steps with potentials that are equally separated from each other. The separation between any two successive reduction steps is -450 50 mV. The low reduction potential (only -0.44 V versus SCE) of the process, that corresponds to the generation of the rt-radical anion 131,109,110,111 and 1121, deserves special attention. 

This behaviour also stands for functionalized [60]fullerene derivatives, with, however, a few striking differences. The most obvious parameter is the negative shift of the reduction potentials, which typically amounts to -100 mV. Secondly, the separation of the corresponding reduction potentials is clearly different. Wlrile the first two reduction steps follow closely the trend noted for pristine [60]fullerene, the remaining four steps display an enlianced separation. This has, again, a good resemblance to the ITOMO-LUMO calculations, namely, a cancellation of the degeneration for functionalized [60]fullerenes [31, 116, 117]. 

The electrochemical features of the next higher fullerene, namely, [70]fullerene, resemble the prediction of a doubly degenerate LUMO and a LUMO + 1 which are separated by a small energy gap. Specifically, six reversible one-electron reduction steps are noticed with, however, a larger splitting between the fourth and fifth reduction waves. It is important to note that the first reduction potential is less negative than that of [60]fullerene [31]. 

Taylor R, Hare J P, Abdul-Sada A K and Kroto H W 1990 Isolation, separation and oharaoterization of the fullerenes Cgg and C g, the 3rd form of oarbon J. Chem. Soc., Chem. Commun. 1423-5... 

Liddell P A, Kuciauskas D, Sumida J P, Nash B, Nguyen D, Moore A L, Moore T A and Gust D 1997 Photoinduced charge separation and charge recombination to a triplet state in a carotene-porphyrin-fullerene triad J. Am. Chem. Soc. 119 1400-5... 

Carbon soot from resistive heating of a carbon rod in a partial helium atmosphere (0.3bar) under specified conditions is extracted with boiling C H or toluene, filtered and the red-brown soln evapd to give crystalline material in 14% yield which is mainly a mixture of fullerenes C q and C70. Chromatographic filtration of the crude mixture with allows no separation of components, but some separation was observed on silica gel... 

Repeated chromatography on neutral alumina yields minor quantities of solid samples of C76, Cg4, C90 and C94 believed to be higher fullerenes. A stable oxide C70O has been identified. Chromatographic procedures for the separation of these compounds are reported. [Science 2S2 548 7997.]... 

Abstract—Carbon nanotubules were produced in a large amount by catalytic decomposition of acetylene in the presence of various supported transition metal catalysts. The influence of different parameters such as the nature of the support, the size of active metal particles and the reaction conditions on the formation of nanotubules was studied. The process was optimized towards the production of nanotubules having the same diameters as the fullerene tubules obtained from the arc-discharge method. The separation of tubules from the substrate, their purification and opening were also investigated. 

The tremendous burst of excitement which attended the initial isolation in 1990 of weighable amounts of separated fullerenes has been followed by an unparalleled and sustained surge of activity as chemists throughout the world rushed to investigate the chemical reactivity of these novel molecular forms of carbon. 

For multielectron-transfer (reversible) processes, the cyclic voltammogram consists of several distinct peaks if the E° values for the individual steps are successively higher and are well separated. An example of such a mechanism is the six-step reduction of the fullerenes C60 and C70 to yield the hexaanion products and C7q. Such six successive reduction peaks are observed in Figure 2-4. 

Recently, photochemical and photoelectrochemical properties of fullerene (Cto) have been widely studied [60]. Photoinduced electron-transfer reactions of donor-Qo linked molecules have also been reported [61-63]. In a series of donor-Cfio linked systems, some of the compounds show novel properties, which accelerate photoinduced charge separation and decelerate charge recombination [61, 62]. These properties have been explained by the remarkably small reorganization energy in their electron-transfer reactions. The porphyrin-Qo linked compounds, where the porphyrin moieties act as both donors and sensitizers, have been extensively studied [61, 62]. 

The only reported X-ray structure of a it-bonded diiodine exists in the 12/coronene associate [75], which shows the I2 to be located symmetrically between the aromatic planes and to form infinite donor/acceptor chains. -Coordination of diiodine over the outer ring in this associate is similar to that observed in the bromine/arene complexes (vide supra), and the I - C separation of 3.20 A is also significantly contracted relative to the stun of their van der Waals radii [75]. For the highly reactive dichlorine, only X-ray structures of its associates are observed with the n-type coordination to oxygen of 1,4-dioxane [76], and to the chlorinated fullerene [77]. 

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