Structures carbon allotropes

Carbon nanotubes (CNTs) as well as fullerenes are splendid gift brought to the Earth from the red giant carbon stars in the long-distant universe through the spectroscopy. Moreover, those belong to new carbon allotropes of the mesoscopic scale with well-defined structures. In particular, CNTs are considered to be the materials appropriate to realise intriguing characteristics related to the mesoscopic system based on their size and physicochemical properties. 

We can understand the differences in properties between the carbon allotropes by comparing their structures. Graphite consists of planar sheets of sp2 hybridized carbon atoms in a hexagonal network (Fig. 14.29). Electrons are free to move from one carbon atom to another through a delocalized Tr-network formed by the overlap of unhybridized p-orbitals on each carbon atom. This network spreads across the entire plane. Because of the electron delocalization, graphite is a black, lustrous, electrically conducting solid indeed, graphite is used as an electrical conductor in industry and as electrodes in electrochemical cells and batteries. Its... 

In 1985, the story of carbon allotropes took a dramatic turn with the discovery of C60, which resulted in a new type of carbon structure, called the fullerenes (Kroto et al., 1985). This discovery earned the 1996 Nobel Prize in chemistry for Harold Kroto, Robert Curl, and... 

Abstract The past two decades have profoundly changed the view that we have of elemental carbon. The discovery of the fullerenes, spherically-shaped carbon molecules, has permanently altered the dogma that carbon can only exist in its two stable natural allotropes, graphite and diamond. The preparation of molecular and polymeric acetylenic carbon allotropes, as well as carbon-rich nanometer-sized structures, has opened up new avenues in fundamental and technological research at the interface of chemistry and the materials sciences. This article outlines some fascinating perspectives for the organic synthesis of carbon allotropes and their chemistry. Cyclo[n]carbons are the first rationally designed molecular carbon allotropes, and... 

N. Dragoe, S. Tanibayashi, K. Nakahara, S. Nakao, H. Shi-motani, L. Xiao, K. Kitazawa, Y. Achiba, K. Kikuchi, K. Nojima, Carbon Allotropes of Dumbbell Structure Cm and Cm , Chem. Commun. 1999, 85-86. 

Shortly after the discovery of the fullerenes in 1985 (Kroto et al., 1985) and especially after their accessibility in macroscopic quantities (Kraetschmer et al., 1990) these new carbon allotropes raised great interest in the chemical world due to their unique structural and electronic properties. As a direct consequence of the curved conjugated n-systcm fullerenes were predicted to be fairly electronegative with the... 

Besides the practical application, the diversity of nanostructured carbon allotropes makes nanocarbon also an ideal model system for the investigation of structure-function correlations in heterogeneous catalysis. Nanocarbons can be tailored in terms of their hybridization state, curvature, and aspect ratio, i.e., dimensions of stacks of basic structural units (BSU), Chapters 1 and 2. The preferred exposition of two types of surfaces, which strongly differ in their physico-chemical behavior, i.e., the basal plane and prismatic edges, can be controlled. Such controlled diversity is seldom found for other materials giving carbon a unique role in this field of basic research. The focus of this chapter is set on the most prominent representatives of the... 

In C60 fullerene-type carbon allotrope, there is only one structure in which all the pentagons are nonadjacent and this is icosohedral symmetry-I (Fig. 4.11). This structure is often referred to as backyball to reflect on its full name buckminster-fullerene (after Buckminster Fuller who popularized the geodesic dome as an architectural form). 

Though Ceo has not (so far) found any major applications, the influence of C6o is now pervasive in chemistry and beyond.8 C6o is a kind of ideal nanoscale building block that can be picked up and manipulated with nanotechnological tools.9 Importantly, its curved, hollow structure has made us familiar with another view of carbon materials, different and complementary to that of flat sheets of carbon atoms in graphite. Ultimately, all the interest generated around such carbon allotropes has driven the research in the field and introduced the perhaps most notable representatives of the present nanoworld, carbon nanotubes (NTs). 

The different structures of the carbon allotropes lead to widely different properties. Because of its three-dimensional network of strong single bonds that tie all atoms in a crystal together, diamond is the hardest known substance. In addition to its use in jewelry, diamond is widely used industrially for the tips of saw blades... 

Haddon, R. C. Raghavachari, K. 1992 Electronic structure of the fullerenes carbon allotropes of intermediate hybridization, buckminsterfullerenes. VCH. (In the press.)... 

The past decade has led to the detection of new carbon allotropes such as fullerenes26 and carbon nanotubes,27 28 in which the presence of five-mem-bered rings allows planar polycyclic aromatic hydrocarbons to fold into bent structures. One notes at the same time that these structures are not objects of controlled chemical synthesis but result from unse-lective physical processes such as laser ablation or discharge in a light arc.29 It should be noted, on the other hand, that, e.g., pyrolytic graphitization processes, incomplete combustion of hydrocarbon precursors yielding carbon black, and carbon fibers30 are all related to mechanisms of benzene formation and fusion to polycyclic aromatic hydrocarbons. 

One may expect that future work on the electrochemistry of diamond should take two paths, namely, an extensive investigation (search for new processes and applications of the carbon allotropes in the electrochemical science and engineering) and intensive one (elucidation of the reaction mechanisms, revealing the effects of crystal structure and semiconductor properties on the electrochemical behavior of diamond and related materials). It is expected that better insight into these effects will result in the development of standard procedures for thin-film-electrodes growth, their characterization, and surface preparation. 

In the solid state, three allotropes of carbon (diamond, graphite, and fullerene Fig. 1) are well-established. Synthetic approaches to other carbon allotropes, including poly-ynes, cvclo[ ]carbons and other carbon networks have been surveyed.1 The chemistry of fullerenes, the so-called third form of carbon, and of the closely related carbon nanotubes, has been extensively detailed.2 4 The molecule C2o may be the smallest fullerene, although other structures have been suggested (Fig. 2).5 It is highly reactive and has been produced in only miniscule amounts in a mass spectrometer from a highly brominated dodecahedrane. 

Although not a perfect fullerene spheroid, another chiral carbon allotrope, C119, was isolated in the form of a 13C-enriched sample from the thermolysis of Ci2o0.74 On grounds of the obtained 13C NMR spectra as well as molecular modeling, Kratschmer and co-workers proposed a C2-symmetric, peanut-shaped structure consisting of two fullerene-like C58 units bridged by three sp3-C-atoms, two of which are symmetry-equivalent.74... 

Figure 5.17 shows a HREM image of a carbon allotrope having a zerodimensional (point) polymer of carbon observed at tire lower part of postshock sample I. The characteristic of the electron diffraction pattern of this type consists of two-dimensional asymmetric (hk) bands and symmetric (0001) reflections of tlie graphite structure and did not alter with tlie angle of tlie incident electron beam. In general, such patterns can be obtained when llie particle is a spherical shell, tlrat is, a zero-dimensional characteristic. Therefore,... 

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