Buckminsterfullerene

In a treatise entitled New Dimensions in Polynudear Aromatic Compounds , Herndon (1988) has described a number of polycyclic conjugated compounds, induding corannulene, a cydacene and CgQ buckminsterfullerene (Osawa 1970 Kroto et al. 1985 Kratschmer et al. 1990) see Fig. 10. The reader understands presumably very well that a full survey of the literature on this interesting molecule (and other fullerenes) is too voluminous (counting thousands of references) to be induded here. In the following small extract the number of Kekule structures K = 12500) for C q is reported (not necessarily as an original finding). 

Schmalz et al. (1986) Hosoya (1986a) Trinajstid, Klein and Randi6 (1986) Klein, Schmalz et al. (1986) Klein, Seitz and Schmalz (1986) Randid, Nikolid and Trinajstid (1987) Aihara and Hosoya (1988) Schmalz et al. (1988) Brendsdal and Cyyin (1989) Klein, Seitz and Schmalz 

The corannulene skeleton (C2q) is recognized as a fragment of CgQ buckminsterfuUerene. This feature has been pointed out several times and is implied, for instance, in a most detailed account of Elemental Carbon Cages by Schmalz et al. (1988). More recent works of rdevance are Diederich and Whetten (1992) Fukushima (1992). Here the former work (Diederich and Whetten 1992) is mentioned particularly because it also includes a comment on [9]cyclacene in connection with higher fullerenes. The work of Feng et al. (1990), which was mentioned under corannulene (Sect. 1.6), has the investigation of C q buckminsterfuUerene as one of its main topics. 

Rice Quantum Institute and Departments of Chemistry and Electrical Engineering, Rice University, Houston, Texas 77251, USA 

The vaporization of carbon has been studied previously in a very similar apparatus. In that work clusters of up to 190 carbon atoms were observed and it was noted that for clusters of more than 40 atoms, only those containing an even number of atoms were observed. In the mass spectra displayed in ref. 6, the Cso peak is the largest for cluster sizes of 40 atoms, but it is not completely dominant. We have recently re-examined this system and found that under certain clustering conditions the C o peak can be made about 40 times larger than neighbouring clusters. 

Our rationalization of these results is that in the laser vaporization, fragments are torn from the surface as pieces of the planar 

When one thinks in terms of the many fused-ring isomers with unsatisfied valences at the edges that would naturally arise from a graphite fragmentation, this result seems impossible there is not much to choose between such isomers in terms of stability. If one tries to shift to a tetrahedral diamond structure, the entire surface of the cluster will be covered with unsatisfied valences. Thus a search was made for some other plausible structure which would satisfy all sp valences. Only a spheroidal structure appears likely to satisfy this criterion, and thus Buckminster Fuller s studies were consulted (see, for example, ref. 7). An unusually beautiful (and probably unique) choice is the truncated icosahedron depicted in Fig. 1. As mentioned above, all valences are satisfied with this structure, and the molecule appears to be aromatic. The structure has the symmetry of the icosahedral group. The inner and outer surfaces are covered with a sea of v electrons. The diameter of this C o molecule is 7 A, providing an inner cavity which appears to be capable of holding a variety of atoms.  

Assuming that our somewhat speculative structure is correct, there are a number of important ramifications arising from the existence of such a species. Because of its stability when formed under the most violent conditions, it may be widely distributed in the Universe. For example, it may be a major constituent of circumstellar shells with high carbon content. It is a feasible constituent of interstellar dust and a possible major site for 

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Sun Y-P, Wang P and Hamilton N B 1993 Fluorescence spectra and quantum yields of Buckminsterfullerene (Cgg) in room-temperature solutions. No excitation wavelength dependence J. Am. Chem. Soc. 115 6378-81... 

FIGURE 11 6 Buckminsterfullerene (Cgo) All carbons are equivalent and no five membered rings are adjacent to one another... 

Speculation about the stability of Ceo centered on the extent to which the aromaticity associated with its 20 benzene rings is degraded by their non planarity and the accompanying angle strain It is now clear that Ceo is a relatively reactive substance reacting with many substances toward which ben zene itself is inert Many of these reactions are char acterized by addition to buckminsterfullerene converting sp hybridized carbons to sp hybridized ones and reducing the overall strain... 

Thus far the importance of carbon cluster chemistry has been in the discovery of new knowl edge Many scientists feel that the earliest industrial applications of the fullerenes will be based on their novel electrical properties Buckminsterfullerene is an insulator but has a high electron affinity and is a superconductor in its reduced form Nanotubes have aroused a great deal of interest for their electrical properties and as potential sources of carbon fibers of great strength... 

Buckminsterfullerene (Chapter 11 essay Carbon Clusters Fullerenes and Nanotubes ) Name given to the Cgo cluster with structure resembling the geodesic domes of R Buck minster Fuller see front cover... 

Ecample Suzuki et. al. used a reaction strategy to expand the Cgo molecule, buckminsterfullerene, by adding divalent carbon equivalents. Adding phenyl diazomethane to Cgo. (I)> followed by the loss of molecular nitrogen, results in a Cgi compound. 

Suzuki, T. Li, Q. Khemani, KC. Wudl, F. Almarsson, O. Systematic Inflation of Buckminsterfullerene CgQi Synthesis of Diphenyl Fulleroids Cgj to Cgg Science, 254 1186-1188, 1991. 

G q Conversion. Buckminsterfullerene can be cmshed to diamond by high pressure appHed at room temperature (40). The process is highly efficient and fast at room temperature, suggesting iadustrial potential. 

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. 

Confirming its structure required isolating enough Cgo to apply modern techniques of structure determination. A quantum leap in fullerene research came in 1990 when a team led by Wolfgang Kratschmer of the Max Planck Institute for Nuclear Physics in Heidelberg and Donald Huffman of the University of Arizona successfully prepared buckmin-sterfullerene in amounts sufficient for its isolation, purification, and detailed study. Not only was the buckminsterfullerene structure shown to be correct. 

Buckminsterfullerene (Cm or Buckyball ) is structurally related to corannulene. In which molecule would you expect 7U-orbital overlap be more effective Explain. How many chemically unique carbons are there in C6o Measure CC bond distances. How many unique distances are there Is each benzene fully delocalized or is one resonance contributor more important than the other ... 

Since the discovery of buckminsterfullerene (C o) [85NAT(318)162] and other fullerenes (Cig. C70), these molecules have been intensely studied, both experimentally and theoretically. Likewise, several reports on heterofullerenes containing heteroatoms such as nitrogen and boron have appeared (91JPC4948 91JPC10564). The incorporation of heteroatoms is expected to modify the structural and electronic features of these structures, and have thus attracted some interest. 

A striking example of the ability of 0s04 to add to unsaturated C-C linkages is provided by its reaction with Qo> buckminsterfullerene (Figure 1.72) [184]... 

Bronsted acid/base catalysis (equation, a, p) 113, 210, 355ff.,360ff., 392 Buckminsterfullerene, reaction with ArN 188... 

Buckminsterfullerene is an allotrope of carbon in which the carbon atoms form spheres of 60 atoms each (see Section 14.16). In the pure compound the spheres pack in a cubic close-packed array, (a) The length of a side of the face-centered cubic cell formed by buckminsterfullerene is 142 pm. Use this information to calculate the radius of the buckminsterfullerene molecule treated as a hard sphere, (b) The compound K3C60 is a superconductor at low temperatures. In this compound the K+ ions lie in holes in the C60 face-centered cubic lattice. Considering the radius of the K+ ion and assuming that the radius of Q,0 is the same as for the Cft0 molecule, predict in what type of holes the K ions lie (tetrahedral, octahedral, or both) and indicate what percentage of those holes are filled. 

Chemists were greatly surprised when soccer-ball-shaped carbon molecules were first identified in 1985, particularly because they might be even more abundant than graphite and diamond The C60 molecule (10) is named buckminsterfullerene after the American architect R. Buckminster Fuller, whose geodesic domes it resembles. Within 2 years, scientists had succeeded in making crystals of buckminsterfullerene the solid samples are called fullerite (Fig. 14.32). The discovery of this molecule and others with similar structures, such as C70, opened up the prospect of a whole new field of chemistry. For instance, the interior of a C60 molecule is big enough to hold an atom of another element, and chemists are now busily preparing a whole new periodic table of these shrink-wrapped atoms. 

FIGURE 14.32 These small crystals are fullerite, in which buckminsterfullerene molecules are packed together in a close-packed lattice. 

Scientists identified the first carbon nanotubes in 1991. They sealed two graphite rods inside a container of helium gas and sent an electric discharge from one rod to the other. Much of one rod evaporated, but out of the inferno some amazing structures emerged (see illustrations). As well as the tiny 60-atom carbon spheres known as buckminsterfullerene—which had been known since 1985—long, hollow, perfectly straight carbon nanotubes were detected. 

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