Fullerene electrochemistry

Yang Y, Arias F, Echegoyen L, Chibante L P F, Flanagan S, Robertson A and Wilson L J 1995 Reversible fullerene electrochemistry correlation with the HOMO-LUMO energy difference for CgQ, C q, Cyg, Cyg and Cg J. Am. Chem. Soc. 117 7801-4... 

While the fullerene electrochemistry was relatively unchanged, a new oxidation peak corresponding to a ferrocene derivation was observed [190]. 

Echegoyen L and Echegoyen L E 1998 Electrochemistry of fullerenes and their derivatives Accou/rfs Chem. Res. 31 593-601 HIrsch A 1994 The Chemistry of the Fuiierenes (Stuttgart Thieme)... 

Electrochemistry of fullerene derivatives with heterocyclic fragments 98ACR593. 

A review9 with more than 37 references includes an examination of symmetry groups and chirality conditions for C60 and C70 bonded to one or two metals in rf and/or rf fashion. Palladium and platinum rf complexes of C6o and C70 are described (novel synthesis, NMR spectra, electrochemistry) as well as first optically active organometallic fullerene derivatives. 

Echegoyen L, Echegoyen LE (1998) Electrochemistry of Fullerenes and Their Derivatives. Acc. Chem. Res. 31 593-601. 

Nagase S, Kobayashi K, Akasaka T, Wakahara T (2000) Endohedral metallofullerenes theory, electrochemistry, and chemical reactions. In Kadish KM, Ruoff RS (eds.) Fullerenes chemistry, physics, and technology. Wiley, New York, pp. 395 136. 

A new class of conjugated hydrocarbons is that of the fullerenes [11], which represent an allotropic modification of graphite. Their electrochemistry has been studied in great detail during the last decade [126]. The basic entity within this series is the Ceo molecule (23). Because of its high electron affinity, it can be reduced up to its hexaanion (Fig. 4) [14,127]. Solid-state measurements indicate that the radical anion of Ceo reversibly dimerizes. NMR measurements confirm a u-bond formation between two radical anion moieties [128,129]. 

Attaching a Ceo cluster to an [Ru(bpy)3] + core has been achieved by 1,3-dipolar cycloaddition of azomethine ylides to the fullerene. The electrochemistry of the complex is complicated a one-electron reversible oxidation of the Ru center, five one-electron reversible reductions associated with the Ceo cage, and five more reversible reductions centered on the bpy ligands. The photophysical properties of the complex have been discussed. ... 

Fig. 5 (a) Electrochemistry of Cgo fullerene, cyclic voltammetry (top) and differential pulse voltammetry (bottom) (Reprinted with permission from [54]). (b) Schematic representation of HOMO and LUMO orbitals after addition of six electrons (red arrows) to the fullerene... 

Similar calculations were made for the only possible isomer of C70 [11-13] that obeys the isolated pentagon rule [4, 6] and for some of the most stable isomers of the higher fullerenes [11, 14-16]. On the basis of their easily accessible LUMOs and high electron affinities, all stable members of the fullerene family were expected to display very rich cathodic electrochemistry. 

Before embarking on a detailed discussion on the electrochemistry of fullerenes, it is important to emphasize that the... 

Cjg, and Cg4 exist as 2, 5, and 24 possible constitutional isomers, respectively a fact that makes separation and purification procedures more difficult. As a result, only a couple of studies have been pubKshed on the electrochemistry of derivatives of the higher fullerenes [44, 54]. 

The discovery of fullerenes in 1985 led to the era of nanomaterials.1 The three-dimensional geometry of these molecules as well as their unique properties distinguishes them from conventional molecules encountered in organic chemistry. Due to recent discoveries in this field, the horizons of this area have broadened to encompass various new molecules such as endohedral fullerenes, nanotubes, carbon nanohorns, and carbon nano-onions. This chapter discusses the electrochemical behavior of some of these carbon nanoparticles with special emphasis on endohedral fullerenes. Since a large number of fullerene derivatives have been prepared and their various electrochemical studies in different solvents and electrolytes have been reported, the electrochemistry of these derivatives is beyond the scope of this text.2 3 Among the other carbon nanoparticles, the electrochemistry of derivatives of carbon nanotubes has been reported. These studies have been highlighted in the final part of the chapter. 

The electrochemistry of C86, C90, and C92 has been reported for isomeric mixtures of individual cages.8 As the cage size of the fullerene increases, the yield of fullerenes decreases significantly. In addition to this, the number of possible isomers also increases, which in turn makes separation of isomers difficult. Thus, no reports appear in the literature indicating the electrochemical behavior of a single isomer of empty... 

The C90 cage has 46 possible constitutional isomers, out of which only five can be isolated. The electrochemistry of C90 shows two oxidations and six reductions. The redox potentials for C90 are given in Table 8.1. The first reduction potential appears at 0.49 V versus ferrocene/ferrocenium, thus making C90 the easiest to reduce among the empty cage fullerenes. 

The biggest fullerene isolated and studied using electrochemistry is C92, which shows eight reversible reductions and one broad irreversible oxidation. The intensities of the eight reduction peaks can be grouped into two distinct sets, thus indicating that the electrochemistry corresponds to a mixture of two isomers The reduction and oxidation potentials are shown in Table 8.1. 

Although carbon nanotubes were discovered soon after fullerenes, not many reports exist in the literature for the solution electrochemistry of these nanoparticles. 

Like the currently popular area, called nanoscience , the field of supramolecular chemistry has rather hazy boundaries. Indeed, both areas now share much common ground in terms of the types of systems that are considered. From the beginning, electrochemistry, which provides a powerful complement to spectroscopic techniques, has played an important role in characterizing such systems and this very useful book goes considerably beyond the volume on this same topic by Kaifer and Gomez-Kaifer that was published about 10 years ago. Some of the classic supramolecular chemistry topics such as rotaxanes, catenanes, host-guest interactions, dendrimers, and self-assembled monolayers remain, but now with important extensions into the realms of fullerenes, carbon nanotubes, and biomolecules, like DNA. 

It is clear that a variety of solvents commonly used in electrochemistry is available for low-temperature studies. Particularly noteworthy are the solvent mixture butyronitrile/ethyl chloride, which can be used down to about 100 K [25,47], and the inclusion of the low-polarity cosolvent, toluene, to enhance the solubility of a substrate that is insoluble in many polar solvents, in this case the fullerene, [50,51]. When low solution resistance is a priority and only moderately low temperatures are needed (above ca. -50°C), polar solvents such as acetonitrile and A Af-dimethylformamide are preferred. 

---