Fullerenes - Carbon Soccer Balls

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. 

This molecular soccer ball was discovered in 1985, as a result of studies into the structures formed by carbon atoms in space, which were in turn prompted by unexplained features in interstellar spectra. 

Harold Kroto expected that chained carbon atoms were present near red giant stars. In order to experimentally demonstrate this hypothesis, he suggested to Richard Smalley, who was investigating clusters generated by irradiating solid materials with laser beams, that they might perform some joint research. Smalley was said to be somewhat reluctant to do so at first, because silicon and germanium were more attractive materials for research than carbon at that time. 

However, mass spectral analysis on some products obtained from irradiating graphite with a powerful laser indicated the presence of an unknown allotrope 

The name buckminsterfullerene was given to this molecule by Kroto due to his knowledge of art and architecture, he noticed that the structure of the molecule was the same as that of the geodesic domes popularized by the famous architect Richard Buckminster Fuller. Over the years, a simphfied version of this name - fullerene - became popular. 

---

Fullerenes - Carbon Soccer Balls As described above, fullerenes are closed structures constructed from pentagonal and hexagonal carbon units. The fullerene consisting of sixty carbon atoms has a structure similar to a soccer ball. Fullerenes possess very different properties to diamond and graphite some of their electronic properties are somewhat similar to those of a semiconductor. 

Feynman s vision of miniaturization and the Drexler-versus-Smalley debate on feasibility of mechanosynthetic reactions using molecular assemblers were discussed. Fullerenes are the third allotropic form of carbon. Soccer-ball-structured Cgo with a surface filled with hexagons and pentagons satisfies Euler s law. Howard patented the first generation combustion synthesis method for fullerene production. The projected price of the fullerenes has decreased from 165,000 per kg to 200 per kg in the second-generation process. Fullerenes can also be synthesized using chemical methods, a supercritical extraction method, and the electric arc process. Applications of fullerenes include high temperature superconductors, bucky onion catalysts, advanced composites and electromechanical systems, synthetic diamonds. 

Fullerenes are described in detail in Chapter 2 and therefore only a brief outline of their structure is presented here to provide a comparison with the other forms of carbon. The C o molecule, Buckminsterfullerene, was discovered in the mass spectrum of laser-ablated graphite in 1985 [37] and crystals of C o were fust isolated from soot formed from graphite arc electrodes in 1990 [38]. Although these events are relatively recent, the C o molecule has become one of the most widely-recognised molecular structures in science and in 1996 the codiscoverers Curl, Kroto and Smalley were awarded the Nobel prize for chemistry. Part of the appeal of this molecule lies in its beautiful icosahedral symmetry - a truncated icosahedron, or a molecular soccer ball, Fig. 4A. 

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. 

Solid carbon materials are available in a variety of crystallographic forms, typically classified as diamond, graphite, and amorphous carbon. More recently another structure of carbon was identified—namely the fullerenes which resemble a soccer ball... 

Fullerenes (originally buckminsterfullerenes) are a new class of carbon-only molecules the first example discovered in 1985 (Kroto et al., 1985), being composed of 60 carbon atoms arranged in a soccer ball structure (C60). The condensed aromatic... 

The 1996 Nobel Prize in chemistry was awarded to three American scientists for their identification of a new allotrope of aromatic carbon molecules called fullerenes. These unusual carbon molecules form a closed-cage structure of joined carbon atoms. The original soccer ball-shaped carbon molecule called buckminsterfullerene contained 60 carbon atoms and was nicknamed Bucky Ball in honor of Buckminster Fuller (1859—1983), who used similar shapes in some of his architectural structures. Since then additional organic pentagon structures beyond the original icosahedral fullerene (C ) have been developed, all with an even... 

The soccer ball shaped framework of Cgg was confirmed for the first time by the X-ray crystal structure of 13 [52]. The bridging of the OSO4 unit occurs in the characteristic 1,2-mode to a [6,6] double bond of the fullerene core. The 17 sets of carbons in the C2v-symmetric 13 were assigned using the 2D NMR INADEQUATE technique on the basis of their connectivities [53]. In these experiments C-enriched material was used. The coupling constants fall into three categories, 48, 54—57 and 65-71 Hz. These values can be attributed to the three types of C-C bonds present in 13, namely C(sp )-C(sp ), the longer [5,6], and the shorter [6,6] bonds, respectively [53]. 

Buckminsterfullerene, or buckyball The simplest form of a fullerene resembles a miniature soccer ball made of 60 carbon atoms stuck together. 

In 1991, scientists at AT T Bell Laboratories discovered a new class of high-temperature superconductors based on fullerene, the allotrope of carbon that contains Cgo molecules (Sections 10.10 and 19.6). Called "buckyballs," after the architect R. Buckminster Fuller, these soccer ball-shaped Cgo molecules react with potassium to give K3C6o- This stable crystalline solid contains a face-centered cubic array of buckyballs, with K+ ions in the cavities between the Cgo molecules (Figure 21.16). At room temperature, K3Q,o is a metallic conductor, but it becomes a superconductor at 18 K. The rubidium fulleride, Rb C o, and a rubidium— thallium-Cfio compound of unknown stoichiometry have higher Tc values of 30 K and 45M8 K, respectively. 

Fullerenes are large molecular carbon cages that are isolated by extraction of specially prepared soot with organic solvents such as benzene. A rich source of fiillerene is soot made by arcing graphite rods in a hehum atmosphere at 200 Torr pressure. The most coimnon fiiUerene is Ceo, which has a truncated icosahedral soccer ball stmcture with icosahedral (4) synunetry. Less synunetrical fiiUerenes with larger numbers of carbon atoms are known. C70 is the next most abundant after Ceo C76 and Cg4 are also known (see Carbon Fullerenes). 

---