Clusters carbon allotropes

A carbon allotrope that contains clusters of 60 carbon atoms bound in a highly symmetrical polyhedral structure... 

The existence of a form of solid carbon where carbynoid species can coexist with sp hybridization has important implications for the achievement of a deeper understanding of the processes leading to the formation of carbon clusters [46], for the synthesis of novel carbon allotropic forms and nanomaterials [1], and for the chemistry of the interstellar medium [12]. 

Another set of carbon allotropes, the fullerenes, consist of carbon atom clusters. These molecules are unusually stable and are an exciting area of research for chemists because of their potential use as superconductors. 

Fullerenes are carbon allotropes discovered in 1985 by Harold W. Kroto, Robert E Curl and Richard E. Smalley. These carbon nanostructures possess icosahedral symmetry and are sp hybridized. Fullerenes have a closed cage-like structure and are examples for zero-dimensional CNMs. Depending on the number of carbon atoms that a cluster possesses, these are named (contains 60 carbon atoms), C (contains 70 carbon atoms), Cg (contains 84 carbon atoms), etc. The unique morphology of these CNMs possess large surface area to volume ratio and is suitable for a wide variety of applications. Synthesis methods of fullerenes are well developed [7-9]. 

Quite apart from the fullerene cluster molecules, numerous other molecular allotropes of carbon, C , have been discovered in the gases formed by the laser vaporization/supersonic expansion of graphite. The products are detected by mass... 

Elementary carbon exists as the allotropes diamond, graphite and the recently characterized series of cluster molecules known as fullerenes, e.g. 

As stated by Smalley, the name [fullerene] was bom in the dimmest early thinking of how a pure carbon cluster of 60 atoms could eliminate its dangling bonds (Billups and Ciufolini, 1993, foreword vi). In an effort to make clear the shape of the cluster, Smalley asked Kroto the name of the architect who worked with big domes. The answer was Buckminister Fuller. Carbon clusters of all sizes were subsequently named Buckminsterfullerenes, fullerenes, or sometimes buckyballs. A third allotrope of carbon had thus been added to the two (graphite and diamond) already known (see Figure 1). 

Buckminsterfullerenes are, by now, well-known allotropes of carbon, especially since they were at the centre of the 1996 Nobel Prize in Chemistry attributed to the British chemist Harold Kroto (1939- ) and to the American chemists Robert Curl (1933- ) and Richard Smalley (1943- ). The Ceo molecule is the best representative of this new class of stable clusters of carbon having the shape of a football ... 

Other recently discovered allotropes include a nanofoam—z web of light magnetic carbon clusters, lonsdaleite—a sort of disfigured hexagonal diamond lattice, and an aggregated diamond nanorod. 

A new trend emerged. The production of intentionally diverse composite carbon films, rich in a variety of graphitic nanostructures, became commonplace. These films contained wide assortments of naturally occurring carbonaceous nanostructures, including but certainly not limited to carbon particles, onions, clusters, fullerenes, nanotubes, and nanofibers. These nanostructured carbon films performed significantly better than both the planar carbon and Spindt metallic emitters with tum-on fields as low as l-5V/pm. Moreover, it was determined that carbon has one of the lowest sputter coefficients [287], making its allotropes extremely stable when bombarded by positive ions associated with local liberated ionized gas species. 

This procedure also produces less stable carbon clusters, such as C70. Buckminsterfullerene can be produced more conveniently using an electric arc between graphite electrodes in an inert gas. The allotrope is soluble in benzene, from which it can be crystallized to give yellow crystals. This solid form is known as fullerite. 

Carbon, nitrogen, oxygen, phosphorus, and sulfur—a cluster of nonmetals in the periodic table (Figure 5.5)—are extremely important elements. Carbon is important because it is the element upon which all life is based. All organic compounds, which encompasses nearly all 13 million compounds that exist (see Chapter 14), contain carbon. Elemental carbon exists as several different allotropes, or different forms of the same element. These include diamond, graphite, and buckminsterfullerene, which is a form more recently synthesized. Inorganic compounds of carbon are also important. These include... 

Most main group elements build solids that are either infinite arrangements or species of low dimensionality-chains or rings-packed in molecular solids. Exceptions to this behavior are carbon and phosphorus which lead to allotropic forms made up of cluster species. The best known of them is the elementary white phosphorus P4 which has a cluster structure itself and retains its shape in solution and in the gas phase. In the case of carbon a new allotropic form consisting of molecular clusters C, the fullerenes, has been discovered recently. These species are giant carbon cages with spherically shaped structures which lead to molecular solids and that are also stable in solution. 

The Discovery of the Fullerenes. In experiments carried out at Rice University in 1985 associated with the presence of carbon in stars and space [Kroto HW, Heath JR, O Brien SC, Curl RF, Smalley RE (1985) Nature 318 162], the Ceo molecule was discovered. This species is one of the many carbon clusters which can be generated when a plasma of carbon vapor produced in the surface of graphite by laser irradiation is cooled by an inert gas jet. The detection of this type of carbon aggregate which appears to constitute a third allotropic and the first molecular form of carbon by mass spectroscopy is illustrated in Fig. 4.18. 

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