Fullerenes chemical reactivity

Due to its rich electronic and electrochemical behavior, and to its versatile chemical reactivity, fullerene Cgo has been considered as the ideal partner in photo-induced processes [28, 111, 112]. Cgo>in fact, is a good electron-acceptor, and has a low reorganization energy [113]. For these reasons, an increasingly high number of donors have been covalently linked to Cgo > for potential use as novel electronic materials and for applications in artificial photosynthesis. Many classes of donor units have been attached to Cgo > including aromatics [ 12, 13, 114-118], porphyrins [11, 119-125] and phthalocyanins [126, 127], rota-xanes [128,129],tetrathiafulvalenes [130-133],carotenes [125],Ru-bipy- [134, 135] and Ru-terpy- [135,136] complexes, as well as ferrocene [130,137]. 

The scope of tire following article is to survey the physical and chemical properties of tire tliird modification of carbon, namely [60]fullerene and its higher analogues. The entluisiasm tliat was triggered by tliese spherical carbon allotropes resulted in an epidemic-like number of publications in tire early to mid-1990s. In more recent years tire field of fullerene chemistry is, however, dominated by tire organic functionalization of tire highly reactive fullerene... 

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. 

From an atomic configuration point of view, a nanotube can be divided into two parts that are generated by curvatures the end caps and sidewall. The end caps are close to the hemispherical fullerene and are curved in 2D, and the sidewall contains less-distorted carbon atoms and is curved in ID (Polizu et al., 2006). Owing to their specific curvatures, the chemical reactivity at the sidewall is significantly lower than that at the end caps The sidewall is thought to be inert and highly reactive agents are required for the covalent functionalization of CNT sidewalls (Wei et al., 2007). 

To separate fuUerene derivatives containing covalently bound groups, HPLC methods are also very important. Addends on the fullerene core have a dramahc influence on the solubility properties and the retenhon behavior. Often, more polar eluents in mixtures or in a pure form can be used and efficient separations on silica gel or several reversed phases (medium polarity), even of different regioisomers of addition products, are possible [220-228], A separahon of Cgg from C70 has also been achieved on the basis of the small difference in their chemical reactivity [229],... 

The UV/Vis spectra (Figure 3.2) of the chestnut brown solutions of the monoadducts CjqHR, particularly the intensive bands at = 213, 257 and 326 nm, are close to those of Cjq, demonstrating their electronic similarity [4]. The biggest changes in the spectra compared with Cjq appear in the visible region. The typical features of Cjq between X = 400 and 700 nm are lost, and a new and very characteristic band at X = 435 nm appears, which is independent of the nature of R. Also, the electrochemical properties of CjqHR are comparable with those of Cjq [5, 19]. The first three reversible reduction waves shift about 100 mV to more negative potentials. Therefore, the fullerene core in these monoadducts still exhibits remarkable electron-acceptor properties, which is one reason for almost the identical chemical reactivity compared with CgQ. 

Fullerenes have potential applications in the preparation of carbon support catalyts and diamond films. They have high electrical conductivity and chemical reactivity. 

Overall, fullerenes and especially Ceo show a chemical reactivity very similar to that of bulky electron-deficient alkenes. They readily react with many electron-rich metal centers to form stable or a complexes. With either bulky or less electron-rich centers, they show a reduced reactivity and form much less stable complexes. 

As a result, the following rules regarding the chemical reactivity mainly of C60, and to a lesser extent to the rest of the family of fullerenes, can be deduced ... 

Cso and its derivatives are also easily excited by low-energy light [x]. Thus, a rational combination of electronic properties with chemical reactivity and/or photoactivity has resulted in the preparation of numerous fullerene-derived materials, including low temperature superconducting salts [xi], radical scavengers [xii], materials for - photovoltaic devices and -> conducting polymers [xiii]. 

Amorphous carbons, carbon black, soot, charcoals, and so on, are forms of graphite or fullerenes. The physical properties depend on the nature and magnitude of the surface area. They show electrical conductivity, have high chemical reactivity due to oxygenated groups on the surface, and readily intercalate other molecules (see later). Graphite and amorphous carbons as supports for Pd, Pt, and other metals are widely used in catalysis and for the preparation of diamond films.18... 

At present, it is still not known why the M C6o-type metallofullerenes behave quite differently from the conventional M C82 type fullerenes in terms, for example, of the solubility property. This may correlate to high reactivity of M C6o toward moisture and/or air M C6o can possibly form weak complexes to stabilize themselves only with pyridine or aniline through their nonbonding electrons. Another possible rationale is that the carbon cage structures of the M C6o so far produced somehow do not satisfy the IPR, which again leads to high chemical reactivity of the species. To fully imderstand "the M C6o mystery" future studies on structural and electronic properties of these elusive metallofullerenes are definitely needed. 

As clarified later, such a classification is reasonable and useful because electron transfers exist from the encaged metallic species to the fullerene cages so that the structures and properties depend strongly on the encapsulated atom(s). Particularly, cluster metallofullerenes show different properties from those containing only metals (mono-metallofullerenes and di-metallofullerenes), which, in return, strongly affects the synthesis and extraction processes, structures, chemical reactivities, and their applications. Consequently, we must, to a certain degree, address cluster metallofullerenes separately in the following text. 

The fullerenes, parttCulabiy Qq, have been well characterized (1-3), but few reports about their chemical reactivity appeared 4-6). It has been proposed that the relatively high electronegativity of this carbon cluster was due to its pyracylene character (2). Further, the inter-five-membered ring bonds are fulvenoid and are potent electrophilic as well as dienophilic and dipolarophilic sites 5, 7). 

Chapter 10, in relation to classical bond orders and bond energies. In the meantime, Chapter 9 deals with the molecular orbital separation, conjugated systems, non-localizable tt molecular orbitals and resonance. In Chapter 11 a brief extension of molecular orbital theory is made to include three categories of systems fullerenes, transition metal complexes, solid aggregates (and band theory). Finally, Chapter 12 mainly illustrates the direct relations between orbitals and chemical reactivity and between orbitals and spectroscopy, with emphasis on electronic transitions and on spectral parameters in NMR spectroscopy. 

Cataldo F. Polyynes production in a solvent-submerged electric arc between graphite electrodes. 3. Chemical reactivity and stability toward air, ozone and light. Fullerenes, Nanotubes and Carbon Nanostructures 2004, 12, 633. 

Except for the fullerenes, carbon nanotubes, nanohoms, and schwarzites, porous carbons are usually disordered materials, and cannot at present be completely characterized experimentally. Methods such as X-ray and neutron scattering and high-resolution transmission electron microscopy (HRTEM) give partial structural information, but are not yet able to provide a complete description of the atomic structure. Nevertheless, atomistic models of carbons are needed in order to interpret experimental characterization data (adsorption isotherms, heats of adsorption, etc.). They are also a necessary ingredient of any theory or molecular simulation for the prediction of the behavior of adsorbed phases within carbons - including diffusion, adsorption, heat effects, phase transitions, and chemical reactivity. 

Babic D, Doslic T, Klein DJ, Misra A (2004) Kekulenoid Addition Patterns for Fullerenes and some Lower Homologs. Bull Chem Soc Japan 77 2003-2010 Balaban AT (1994) Reaction graphs. Graph Theoretical Approaches to Chemical Reactivity. Ed. D. Bonchev O. Mekenyan, Kluwer Academic Publishers Dordrecht pp 137-180... 

ORGANOMETALLIC COMPLEXES OF FULLERENES VI. Physical Properties and Chemical Reactivity... 

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