Allotropic forms of carbon

If you re a sports fan, you ve almost certainly seen this structure before. It is that of a soccer ball with a carbon atom at each vertex. Smalley and his colleagues could have named this allotropic form of carbon "carbosoccer" or "soc-cerene," but they didn t. Instead they called it "buckminster fullerene" after the architect R. Buckminster Fuller, whose geodesic domes vaguely resembled truncated soccer balls. 

The state of research on the two classes of acetylenic compounds described in this article, the cyclo[ ]carbons and tetraethynylethene derivatives, differs drastically. The synthesis of bulk quantities of a cyclocarbon remains a fascinating challenge in view of the expected instability of these compounds. These compounds would represent a fourth allotropic form of carbon, in addition to diamond, graphite, and the fullerenes. The full spectral characterization of macroscopic quantities of cyclo-C should provide a unique experimental calibration for the power of theoretical predictions dealing with the electronic and structural properties of conjugated n-chromophores of substantial size and number of heavy atoms. We believe that access to bulk cyclocarbon quantities will eventually be accomplished by controlled thermal or photochemical cycloreversion reactions of structurally defined, stable precursor molecules similar to those described in this review. 

The Nobel prize in Chemistry for the year 1996 was awarded for the discovery of the fullerenes, the third allotropic form of carbon, with Cgo and C70 as the two most prominent representatives. While the fullerenes of course are the epitome of carbon-rich molecular compounds, it is an irony that their synthesis is more of a physical phase transition, taking place under drastic conditions [1]. 

There are other allotropic forms of carbon, including graphite, Wurzite carbon... 

Fullerenes, the third allotropic form of carbon along with graphite and diamond, are a novel class of spheroidally shaped molecules made exclusively of carbon atoms. They have generated much enthusiasm and numerous research efforts during the past few years.206 Hence, the chemical and physical features of C6o, also named... 

In 1985, another allotropic form of carbon, fullerenes, were discovered. Two important fullerenes are C60 and C70. 

V.I. Sokolov, I.V. Stankevich. Fullerenes - new allotropic forms of carbon structure, electron structure and chemical properties. // Success in chemistry, 1993, v.62, N°5, p.455-473. 

The toxicity of this third allotropic form of carbon is an aspect related to application in medicine and biology, while the concern about the environmental impact is due to the industrial production of fullerenes. Many studies are dedicated to both aspects and, so far, it is not possible to have a definitive answer although the current findings allow some optimistic vision. 

Once upon a time there were three brilliant researchers who isolated and identified the third allotropic form of carbon. C60 fulleiene is the most common compound of this family and, since its discovery it has attracted glances and attentions from the scientific community for its biological potentialities (Fig. 1.5). 

The emerging field of nanotechnology is affirming its increasing importance day by day. In this context fullerenes and carbon nano tubes (CNTs) play an important role. These new allotropic forms of carbon have been discovered in the last two decades, and, since then, they have stimulated the curiosity and interest of physicists and chemists. 

Figure 4.19 shows four allotropic forms of carbon. Allotropes are different crystalline or molecular forms of the same element that differ in physical and chemical properties. 

In 1799 Guyton de Morveau converted the diamond first into graphite and finally into carbonic acid (carbon dioxide). He did not realize, however, that graphite is merely another allotropic form of carbon, but regarded it as partially oxidized carbon (263, 264). 

No other allotropic forms of carbon were known until ten years ago then arising from studies of interstellar carbonaceous molecules, a new form of carbon, namely fullerene or buckyballs , was discovered (Kroto et al 1985), for which the authors received the 1996 Nobel Prize for Chemistry. Its structure is basically a ball or spherically shaped cage consisting of pure carbon. The most stable... 

Sladkov AM (2003) Carbyne the third allotropic form of carbon. Nauka, Moscow [in Russian]... 

As allotropic forms of carbon, graphite is gray and slippery, while diamond is clear, hard, and an excellent conductor of heat. 

El Goresy, A. Donnay, G. 1968 A new allotropic form of carbon from the Ries crater. Science, Wash. 161, 363-364. 

The fee unit cell can be thought of as having holes in which other atoms or ions can be placed. For example, the Na + ions occupy octahedral holes in the fee CF lattice (connecting the six CF ions surrounding a Na+ by lines defines an octahedron). The fee lattice also has tetrahedral holes if we divide the unit cell into 8 smaller cubes, the centers of these little cubes are surrounded by 4 lattice points which define a tetrahedron. The diamond allotropic form of carbon has a fee structure with C atoms in 4 of these tetrahedral sites each C atom is surrounded by (covalently bound to) 4 other C s. 

Allotropic forms of carbon. In the solid state, the element carbon exists in three different allotropic modifications—amorphous carbon and the two crystalline forms known as diamond and graphite. Amorphous carbon includes numerous common products such as wood charcoal, bone black, coke, lamp black, and carbon black. Each of these varieties of crystalline and amorphous carbon possesses properties that render it useful for a variety of purposes. 

Fullerenes were first identified by Smalley and coworkers in 1985. Although a later section in this chapter will be devoted to this topic, it is briefly mentioned here because C60 is an allotropic form of carbon. The structure of this form of carbon is shown in Figure 10.4. 

We used to believe that there are three allotropic forms of carbon graphite, diamond, and amorphous carbon. However, an important new carbon al-lotrope, the fullerenes, was discovered as recently as the 1980s. The most famous fullerene is buckminsterfullerene, Ceo, which is depicted in Fig. 3.1. The structure of this soccer ball-shaped molecule consists of a sphere of sixty carbon atoms arranged in pentagons and hexagons each carbon pentagon is surrounded by five carbon hexagons. 

Carbon materials liave particular characteristics due to differences in chemical bond formation. Allotropic forms of carbon drat luive been discovered can be categorized into five types from file standpoint of the type of hybridization of the valence orbitals (1) sp -hybridization (2) sp -hybridization (3) sp-hybrid-ization (4) mixed hybridization (sp + sp ) and (5) a valance state characterized by a fractional degree of hybridization (sp , where 1 diamond-like carbon, and fullcrcnes correspond to groups (1), (3), (4), and (5), respectively. 

A LONG search for molecular allotropic forms of carbon culminated in the discovery of a method for preparing large quantities of the C o molecule and the subsequent confirmation of its cage-like truncated-icosahedral structure. The 70 molecule prepared by the same method was later also isolated and found to have the predicted cylindrical structure. Incomplete... 

The fullerenes, which contain only carbon, are an allotropic form of carbon discovered in 1985. All the fullerenes have even numbers of atoms, with formulas ranging up to C400 and higher. Their tt bonds are conjugated tr electron systems. 

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