|
Results for fullerene
|
On this page:
|
Any of various cagelike, hollow molecules composed of hexagonal and pentagonal groups of atoms, and especially those formed from carbon, that constitute the third form of carbon after diamond and graphite.
[After Richard Buckminster FULLER (from the resemblance of their configurations to his geodesic domes) + –ENE.]
A hollow, pure carbon molecule in which the atoms lie at the vertices of a polyhedron with 12 pentagonal faces and any number (other than one) of hexagonal faces. The molecule was named after R. Buckminster Fuller, the inventor of geodesic domes, which conform to the same underlying structural formula.
Buckminsterfullerene (C60 or fullerene-60; Fig. 1) is the archetypal member of the fullerenes. Other stable members of the fullerene family have similar structures (Fig. 2). The fullerenes can be considered, after graphite and diamond, to be the third well-defined allotrope of carbon. Macroscopic amounts of various fullerenes were first isolated in 1990, and since that time it has been discovered that members of this class of spheroidal organic molecules have numerous novel physical and chemical properties. The fullerenes promise to have synthetic, pharmaceutical, and industrial applications. Derivatives have been found to exhibit fascinating electrical and magnetic behavior, in particular superconductivity and ferro-magnetism. See also Carbon; Graphite.
Structure of fullerene-60 (C60).
Some of the more stable members of the fullerene family. (a) C28. (b) C32. (c) C50. (d) C60. (e) C70.
Structures and properties
In the fullerene molecule an even number of carbon atoms are arrayed over the surface of a closed hollow cage. Each atom is trigonally linked to its three near neighbors by bonds that delineate a polyhedral network, consisting of 12 pentagons and n hexagons. (Such structures conform to Euler's theorem for polyhedrons in that n may be any number other than one including zero.) All 60 atoms in fullerene-60 are equivalent and lie on the surface of a sphere distributed with the symmetry of a truncated icosahedron. The 12 pentagons are isolated and interspersed symmetrically among 20 linked hexagons.
In benzene solution, fullerene-60 is magenta and fullerene-70 red. Fullerene-60 forms translucent magenta face-centered cubic (fcc) crystals that sublime. The ionization energy is 7.61 eV and the electron affinity is 2.6–2.8 eV. The strongest absorption bands lie at 213, 257, and 329 nanometers. Studies with nuclear magnetic resonance spectroscopy yield a chemical shift of 142.7 parts per million; this result is commensurate with an aromatic system.
Solid C60 exhibits interesting dynamic behavior in that at room temperature the individual round molecules in the face-centered cubic crystals are rotating isotropically (that is, freely) at around 108 Hz. At around 260 K (8.3°F) there is a phase transition to a simple cubic (sc) lattice accompanied by an abrupt lattice contraction. Rotation is no longer free, and the individual molecules make rotational jumps between two favored (relative) orientational configurations—in the lower-energy one a double bond lies over a pentagon, and in the other it lies over a hexagon. At 90 K (−300°F) the individual molecules stop rotating altogether, freezing into an orientationally disordered crystal involving a mix of the two configurations.
Chemistry and formation
Fullerene-60 behaves as a soft electrophile, a molecule that readily accepts electrons during a primary reaction step. It can readily accept three electrons and perhaps even more. The molecule can be multiply hydrogenated, methylated, ammonated, and fluorinated. It forms exohedral complexes in which an atom (or group) is attached to the outside of the cage, as well as endohedral complexes in which an atom is trapped inside the cage.
The C60 molecule behaves as though it has only a single resonance form—one in which the 30 double bonds are localized in the bonds that interconnect the pentagons. This is a key factor, as addition to these double bonds is the most important reaction as far as the application of C60 in synthesis is concerned.
On exposure of C60 to certain alkali and alkaline earth metals, exohedrally doped crystalline materials are produced that exhibit superconductivity at relatively high temperatures (10 to 33 K or −440 to −400°F). The C60 molecule has a triply degenerate lowest unoccupied molecular orbital (LUMO), which in the superconducting materials is half filled, containing three electrons. Other ionic phases, such as MnC60 (n = 1, 2, 4, 6, where M is the intercalated metal atom), exist but are not superconducting—they appear to be metallic or semiconductor/insulators. See also
Perhaps the most important aspect of the fullerene discovery is that the molecule forms spontaneously. This fact has important implications for understanding the way in which extended carbon materials form, and in particular the mechanism of graphite growth and the synthesis of large polycyclic aromatic molecules. It has become clear that as far as pure carbon aggregates of around 60–1000 atoms are concerned, the most stable species are closed-cage fullerenes.
For more information on fullerene, visit Britannica.com.
The most common and most stable fullerene is buckminsterfullerene, a spheroidal molecule, resembling a soccer ball, consisting of 60 carbon atoms. Buckminsterfullerene is the most abundant cluster of carbon atoms found in carbon soot. It is also the smallest carbon molecule whose pentagonal faces are isolated from each other. Other fullerenes that have been produced in macroscopic amounts have 70, 76, 84, 90, and 96 carbon atoms, and much larger fullerenes have been found, such as those that contain 180, 190, 240, and 540 carbon atoms.
Fullerenes were first identified in 1985 as products of experiments in which graphite was vaporized using a laser, work for which R. F. Curl, Jr., R. E. Smally, and H. W. Kroto shared the 1996 Nobel Prize in Chemistry. Fullerenes have since been discovered in nature as a result of lightning strikes, in the residue produced by carbon arc lamps, in interstellar dust, and in meteorites.
Fullerene chemistry involves substituting metal atoms for one or more carbon atoms in the molecule to produce compounds called fullerides. Among these are conducting films of alkali metal-doped fullerenes and superconductors (potassium-doped Tc 18K, rubidium-doped Tc 30K). Fullerenes also have been used to produce tiny diamonds and thin diamond films. Fullerene research is expected to lead to new materials, lubricants, coatings, catalysts, electro-optical devices, and medical applications.
Bibliography
See M. S. Dresselhaus et al., Science of Fullerenes and Carbon Nanotubes (1996); H. W. Kroto, The Fullerenes: New Horizons for the Chemistry, Physics, and Astrophysics of Carbon (1997); R. Taylor, ed., Lecture Notes on Fullerene Chemistry (1999).
 |
| Topics |
|---|
| History · Implications Applications · Organizations Popular culture · List of topics |
| Subfields and related fields |
| Nanomedicine Molecular self-assembly Molecular electronics Scanning probe microscopy Nanolithography Molecular nanotechnology |
| Nanomaterials |
| Nanomaterials · Fullerene Carbon nanotubes Nanotube membranes Fullerene chemistry Applications · Popular culture Timeline · Carbon allotropes Nanoparticles · Quantum dots Colloidal gold · Colloidal silver |
| Molecular nanotechnology |
| Molecular assembler Mechanosynthesis Nanorobotics · Grey goo K. Eric Drexler Engines of Creation |
|
|
The fullerenes, discovered in 1985 by Robert Curl, Harold Kroto and Richard Smalley at the University of Sussex and Rice University, are a family of carbon allotropes named after Richard Buckminster Fuller and are sometimes called buckyballs. They are molecules composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Cylindrical fullerenes are called carbon nanotubes or buckytubes. Fullerenes are similar in structure to graphite, which is composed of a sheet of linked hexagonal rings, but they contain also pentagonal (or sometimes heptagonal) rings that prevent the sheet from being planar.
In molecular beam experiments, discrete peaks were observed corresponding to molecules with the exact mass of sixty or seventy or more carbon atoms. In 1985, Harold Kroto (then of the University of Sussex, now of Florida State University), James R. Heath, Sean O'Brien, Robert Curl and Richard Smalley, from Rice University, discovered C60, and shortly thereafter came to discover the fullerenes. Kroto, Curl, and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of this class of compounds. C60 and other fullerenes were later noticed occurring outside the laboratory (e.g., in normal candle soot). By 1991, it was relatively easy to produce gram-sized samples of fullerene powder using the techniques of Donald Huffman and Wolfgang Krätschmer. Fullerene purification remains a challenge to chemists and to a large extent determines fullerene prices. So-called endohedral fullerenes have ions or small molecules incorporated inside the cage atoms. Fullerene is an unusual reactant in many organic reactions such as the Bingel reaction discovered in 1993.
The existence of C60 was predicted in 1970 by Eiji Osawa of Toyohashi University of Technology. He noticed that the structure of a corannulene molecule was a subset of a soccer-ball shape, and he made the hypothesis that a full ball shape could also exist. His idea was reported in Japanese magazines, but did not reach Europe or America.
Buckminsterfullerene (C60) was named after Richard Buckminster Fuller, a noted architect who popularized the geodesic dome. Since buckminsterfullerenes have a similar shape to that sort of dome, the name was thought to be appropriate. As the discovery of the fullerene family came after buckminsterfullerene, the name was shortened to illustrate that the latter is a type of the former.
For illustrations of geodesic dome structures, see Montreal Biosphere, Eden Project, Missouri Botanical Gardens, Science World at TELUS World of Science, Mitchell Park Horticultural Conservatory, Gold Dome, Tacoma Dome, and Spaceship Earth (Disney).
Buckminsterfullerene (IUPAC name (C60-Ih)[5,6]fullerene) is the smallest fullerene molecule in which no two pentagons share an edge (which can be destabilizing; see pentalene). It is also the most common in terms of natural occurrence, as it can often be found in soot.
The structure of C60 is a truncated (T = 3) icosahedron, which resembles a soccer ball of the type made of hexagons and pentagons, with a carbon atom at the vertices of each polygon and a bond along each polygon edge.
The van der Waals diameter of a C60 molecule is about 1 nanometer (nm). The nucleus to nucleus diameter of a C60 molecule is about 0.7 nm.
The C60 molecule has two bond lengths. The 6:6 ring bonds (between two hexagons) can be considered "double bonds" and are shorter than the 6:5 bonds (between a hexagon and a pentagon).
Nanotubes are cylindrical fullerenes. These tubes of carbon are usually only a few nanometres wide, but they can range from less than a micrometre to several millimetres in length. They often have closed ends, but can be open-ended as well. There are also cases in which the tube reduces in diameter before closing off. Their unique molecular structure results in extraordinary macroscopic properties, including high tensile strength, high electrical conductivity, high ductility, high resistance to heat, and relative chemical inactivity (as it is cylindrical and 'planar' — that is, it has no 'exposed' atoms that can be easily displaced). One proposed use of carbon nanotubes is in paper batteries , developed in 2007 by researchers at Rensselaer Polytechnic Institute.
A new type of buckyball utilizing boron atoms instead of the usual carbon has been predicted and described by researchers at Rice University. The B-80 structure is predicted to be more stable than the C-60 buckyball. [1] One reason for this given by the researchers is that the B-80 is actually more like the original geodesic dome structure popularized by Buckminster Fuller which utilizes triangles rather than hexagons.
In mathematical terms, the structure of a fullerene is a trivalent convex polyhedron with pentagonal and hexagonal faces. In graph theory, the term fullerene refers to any 3-regular, planar graph with all faces of size 5 or 6 (including the external face). It follows from Euler's polyhedron formula, |V|-|E|+|F| = 2, (where |V|, |E|, |F| indicate the number of vertices, edges, and faces), that there are exactly 12 pentagons in a fullerene and |V|/2-10 hexagons.
The smallest fullerene is the dodecahedron--the unique C20, dodecahedrane. There are no fullerenes with 22 vertices. The number of fullerenes C2n grows with increasing n = 12,13,14..., roughly in proportion to n9. For instance, there are 1812 non-isomorphic fullerenes C60. Note that only one form of C60, the buckminsterfullerene alias truncated icosahedron, has no pair of adjacent pentagons (the smallest such fullerene). To further illustrate the growth, there are 214,127,713 non-isomorphic fullerenes C200, 15,655,672 of which have no adjacent pentagons.
For the past decade, the chemical and physical properties of fullerenes have been a hot topic in the field of research and development, and are likely to continue to be for a long time. Popular Science has published articles about the possible uses of fullerenes in armor.[citation needed] In April 2003, fullerenes were under study for potential medicinal use: binding specific antibiotics to the structure to target resistant bacteria and even target certain cancer cells such as melanoma. The October 2005 issue of Chemistry and Biology contains an article describing the use of fullerenes as light-activated antimicrobial agents.[2]
In the field of nanotechnology, heat resistance and superconductivity are some of the more heavily studied properties.
A common method used to produce fullerenes is to send a large current between two nearby graphite electrodes in an inert atmosphere. The resulting carbon plasma arc between the electrodes cools into sooty residue from which many fullerenes can be isolated.
There are many calculations that have been done using ab-initio Quantum Methods applied to fullerenes. By DFT and TDDFT methods one can obtain IR, Raman and UV spectra. Results of such calculations can be compared with experimental results.
Researchers have been able to increase the reactivity of fullerenes by attaching active groups to their surfaces. Buckminsterfullerene does not exhibit "superaromaticity": that is, the electrons in the hexagonal rings do not delocalize over the whole molecule.
A spherical fullerene of n carbon atoms has n pi-bonding electrons. These should try to delocalize over the whole molecule. The quantum mechanics of such an arrangement should be like one shell only of the well-known quantum mechanical structure of a single atom, with a stable filled shell for n = 2, 8, 18, 32, 50, 72, 98, 128, etc, i.e. twice a perfect square; but this series does not include 60. As a result, C60 in water tends to pick up two more electrons and become an anion. The nC60 described below may be the result of C60's trying to form a metallic bonding type loose combination.
Fullerenes are stable, but not totally nonreactive. The sp2-hybridized carbon atoms, which are at their energy minimum in planar graphite, must be bent to form the closed sphere or tube, which produces angle strain. The characteristic reaction of fullerenes is electrophilic addition at 6,6-double bonds, which reduces angle strain by changing sp2-hybridized carbons into sp3-hybridized ones.[1] The change in hybridized orbitals causes the bond angles to decrease from about 120 degrees in the sp2 orbitals to about 109.5 degrees in the sp3 orbitals. This decrease in bond angles allows for the bonds to bend less when closing the sphere or tube, and thus, the molecule becomes more stable.
Other atoms can be trapped inside fullerenes to form inclusion compounds known as endohedral fullerenes. An unusual example is the egg shaped fullerene Tb3N@C84, which violates the isolated pentagon rule [3] Recent evidence for a meteor impact at the end of the Permian period was found by analysing noble gases so preserved.[4] Metallofullerene-based inoculates using the rhonditic steel process are beginning production as one of the first commercially-viable uses of buckyballs.
Fullerenes are sparingly soluble in many solvents. Common solvents for the fullerenes include aromatics such as toluene and carbon disulfide. Solutions of pure Buckminsterfullerene have a deep purple color. Solutions of C70 are a reddish brown. The higher fullerenes C76 to C84 have a variety of colors. C76 has two optical forms, while other higher fullerenes have several structural isomers. Fullerenes are the only known allotrope of carbon that can be dissolved in common solvents at room temperature.
Some fullerene structures are not soluble because they have a small bandgap between the ground and excited states. These include the small fullerenes C36 and C50. The C72 structure is also in this class, but the endohedral version with a trapped lanthanide-group atom is soluble due to the interaction of the metal atom and the electronic states of the fullerene. Researchers had originally been puzzled by C72 being absent in fullerene plasma-generated soot extract, but found in endohedral samples. Small band gap fullerenes are highly reactive and bind to other fullerenes or to soot particles.
Solvents that are able to dissolve a fullerene extract mixture (C60 / C70) are listed below in order from highest solubility. The value in parentheses is the approximate saturated concentration.
In 1999, researchers from the University of Vienna demonstrated that the wave-particle duality applied to molecules such as fullerene[5]. One of the co-authors of this research, Julian Voss-Andreae became an artist and has since created several sculptures symbolizing wave-particle duality in Buckminsterfullerenes.
Science writer Marcus Chown made a reference on the CBC radio show "Quirks And Quarks" in May 2006 that there is a scientist working on having buckyballs follow the quantum behavior of atoms of appearing to be in two places at once. The work is continuing on this phenomenon.[6].
Although fullerene C60 had been previously shown to be non-toxic, a presentation given to the American Chemical Society in March 2004 and described in an article in New Scientist on April 3 2004, suggested the molecule may have cytotoxic properties. An experiment by Eva Oberdörster at Southern Methodist University, which introduced a water soluble suspension of nanoparticles (25 nm - 100 nm) of fullerenes (which they termed nano-C60, or nC60) into water at concentrations of 0.5 parts per million, found that largemouth bass suffered a 17-fold increase in cellular damage in the brain tissue after 48 hours. This work gained much attention, but it was later shown by several groups that the toxicity observed was most likely due to the use of tetrahydrafuran (THF) to prepare the "nano-C60" water soluble solution used in the tests. See for example Isakovic, et al., Biomaterials, 27, 5049-5058, 2006, where this phenomenon is reviewed, and which gives results showing that removal of THF resulted in a loss of toxicity. Moussa et al., also provide a comprehensive review of fullerene toxicity in "Toxicity Studies of Fullerenes and Derivatives," a chapter from the book "Bio-applications of Nanoparticles" (Chan ed., Landes Bioscience, 2007). In this review, the authors review the work on fullerene toxicity beginning in the early 1990's to present, including the work of Oberdorster, Colvin and others that gave rise to questions on the toxicity of C60, and conclude that the evidence gathered since the discovery of fullerenes overwhelmingly points to C60 being non-toxic.
Examples of fullerenes in popular culture are numerous. In fact, fullerenes appeared in fiction well before science started to take serious interest in them.
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Join the WikiAnswers Q&A community. Post a question or answer questions about "fullerene" at WikiAnswers.
Copyrights:
 |
 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
 |
| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
 |
| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more |
 |
| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/ Read more |
 |
| Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Fullerene". Read more |
Search for answers directly from your browser with the FREE Answers.com Toolbar!
Click here to download now. 
Get Answers your way! Check out all our free tools and products.
Mentioned In:
