View source for Fullerene

{{short description|Allotrope of carbon}}
{{Use dmy dates|date=February 2015}}
[[File:C60 Molecule.svg|thumb|[[Ball-and-stick model]] of the C<sub>60</sub> fullerene (buckminsterfullerene).|alt=]]
[[File:C20 Fullerene.png|thumb|Ball-and-stick model of the C<sub>20</sub> fullerene.|alt=]]
[[File:Carbon nanotube zigzag povray cropped.PNG|thumb|right|[[Space-filling model]] of a carbon nanotube.]]
[[File:C60-Fulleren-kristallin.JPG|thumb|C<sub>60</sub> fullerite (bulk solid C<sub>60</sub>).|alt=]]
{{Nanomaterials}}
A '''fullerene''' is an [[allotropes of carbon|allotrope of carbon]] whose molecules consist of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with [[fused rings]] of five to six atoms. The molecules may have hollow [[sphere]]- and [[ellipsoid]]-like forms, [[cylinder (geometry)|tube]]s, or other shapes.

Fullerenes with a closed mesh topology are informally denoted by their [[empirical formula]] C<sub>''n''</sub>, often written C''n'', where ''n'' is the number of carbon atoms. However, for some values of ''n'' there may be more than one [[isomer]].

The family is named after [[buckminsterfullerene]] (C<sub>60</sub>), the most famous member, which in turn is named after [[Buckminster Fuller]]. The closed fullerenes, especially C<sub>60</sub>, are also informally called '''buckyballs''' for their resemblance to the standard [[ball (association football)|ball]] of [[association football]]. Nested closed fullerenes have been named '''bucky onions'''. Cylindrical fullerenes are also called [[carbon nanotubes]] or '''buckytubes'''.<ref>{{Cite web |url=https://www.merriam-webster.com/dictionary/buckytube |title=Definition of BUCKYTUBE |website=www.merriam-webster.com}}</ref> The bulk solid form of pure or mixed fullerenes is called '''fullerite'''.<ref>{{Cite web |title=fullerite |url=https://eng.thesaurus.rusnano.com/wiki/article1935 |archive-url=https://web.archive.org/web/20151023072444/http://eng.thesaurus.rusnano.com/wiki/article1935 |archive-date=23 October 2015}}</ref>

Fullerenes had been predicted for some time, but only after their accidental synthesis in 1985 were they detected in nature<ref name="buseck1992">{{Cite journal |last1=Buseck |first1=P.R. |last2=Tsipursky |first2=S.J. |last3=Hettich |first3=R. |year=1992 |title=Fullerenes from the Geological Environment |journal=[[Science (journal)|Science]] |volume=257 |issue=5067 |pages=215–7 |bibcode=1992Sci...257..215B |doi=10.1126/science.257.5067.215 |pmid=17794751 |s2cid=4956299}}</ref><ref name="invWeb2010">{{Cite web |title=The allotropes of carbon |url=http://invsee.asu.edu/nmodules/Carbonmod/everywhere.html |archive-url=https://web.archive.org/web/20100618165649/http://invsee.asu.edu/nmodules/Carbonmod/everywhere.html |archive-date=18 June 2010 |access-date=29 August 2010 |website=Interactive Nano-Visualization in Science & Engineering Education }}</ref> and outer space.<ref name="cami2010">{{Cite journal |last1=Cami |first1=J |last2=Bernard-Salas |first2=J. |last3=Peeters |first3=E. |last4=Malek |first4=S. E. |date=2 September 2010 |title=Detection of {{chem|C|60}} and {{chem|C|70}} in a Young Planetary Nebula |journal=[[Science (journal)|Science]] |volume=329 |issue=5996 |pages=1180–1182 |doi=10.1126/science.1192035 |pmid=20651118 |s2cid=33588270}}</ref><ref name="bbc2010">[https://www.bbc.co.uk/news/science-environment-10730280 Stars reveal carbon 'spaceballs'], BBC, 22 July 2010.</ref> The discovery of fullerenes greatly expanded the number of known [[allotropes of carbon]], which had previously been limited to [[graphite]], <!--not graphene discovered later-->[[diamond]], and [[amorphous solid|amorphous]] carbon such as [[soot]] and [[charcoal]]. They have been the subject of intense research, both for their chemistry and for their technological applications, especially in [[materials science]], [[electronics]], and [[nanotechnology]].<ref>{{Cite journal |last1=Belkin |first1=A. |last2=et. |first2=al. |date=2015 |title=Self-Assembled Wiggling Nano-Structures and the Principle of Maximum Entropy Production |journal=Sci. Rep. |volume=5 |article-number=8323 |bibcode=2015NatSR...5.8323B |doi=10.1038/srep08323 |pmc=4321171 |pmid=25662746}}</ref>

==Definition==
IUPAC defines fullerenes as "polyhedral closed cages made up entirely of n three-coordinate carbon atoms and having 12 pentagonal and (n/2-10) hexagonal faces, where n ≥ 20."<ref>{{cite journal |last1=Godly |first1=E.W. |last2=Taylor |first2=R. |year=1997 |title=Nomenclature and Terminology of Fullerenes |journal=Pure and Applied Chemistry |volume=69 |issue=7 |pages=1411–1434 |doi=10.1351/pac199769071411 |s2cid=94299129 |url=https://publications.iupac.org/pac/1997/pdf/6907x1411.pdf}}</ref>

==History==
[[Image:Fullerene c540.png|thumb|The [[icosahedron|icosahedral]] fullerene {{chem|C|540}}, another member of the family of fullerenes]]

===Predictions and limited observations===
The icosahedral {{chem|C|60|H|60}} cage was mentioned in 1965 as a possible topological structure.<ref>{{Cite journal |last=Schultz |first=H.P. |year=1965 |title=Topological Organic Chemistry. Polyhedranes and Prismanes |journal=[[Journal of Organic Chemistry]] |volume=30 |issue=5 |pages=1361–1364 |doi=10.1021/jo01016a005}}</ref> [[Eiji Osawa]] predicted the existence of {{chem|C|60}} in 1970.<ref>{{Cite journal |last=Osawa |first=E. |year=1970 |title=Superaromaticity |journal=Kagaku |volume=25 |pages=854–863}}</ref><ref>{{Cite journal |last=Halford |first=B. |date=9 October 2006 |title=The World According to Rick |url=http://pubs.acs.org/cen/coverstory/84/8441cover.html |journal=[[Chemical & Engineering News]] |volume=84 |issue=41 |pages=13–19 |doi=10.1021/cen-v084n041.p013|url-access=subscription }}</ref> He noticed that the structure of a [[corannulene]] molecule was a subset of the shape of a football, and hypothesised that a full ball shape could also exist. Japanese scientific journals reported his idea, but neither it nor any translations of it reached Europe or the Americas.

Also in 1970, [[R. W. Henson]] (former member of the [[United Kingdom|UK]] [[Atomic Energy Research Establishment]]<ref>{{Cite web |title=Bob Henson |url=http://www.solina.demon.co.uk/bob.htm |archive-url=https://web.archive.org/web/20121211051020/http://www.solina.demon.co.uk/bob.htm |archive-date=2012-12-11 |access-date=2025-07-16 |website=www.solina.demon.co.uk}}</ref>) proposed the {{chem|C|60}} structure and made a model of it. Unfortunately, the evidence for that new form of carbon was very weak at the time, so the proposal was met with skepticism, and was never published. It was acknowledged only in 1999.<ref>{{Cite journal |last=Thrower |first=P.A. |author-link=Peter Thrower |year=1999 |title=Editorial |journal=[[Carbon (journal)|Carbon]] |volume=37 |issue=11 |pages=1677–1678 |doi=10.1016/S0008-6223(99)00191-8|bibcode=1999Carbo..37.1677. }}</ref><ref>{{Cite web |last=Henson |first=R.W. |title=The History of Carbon 60 or Buckminsterfullerene |url=http://www.solina.demon.co.uk/c60.htm |archive-url=https://web.archive.org/web/20130615212528/http://www.solina.demon.co.uk/c60.htm |archive-date=15 June 2013}}</ref>

In 1973, independently from Henson, D. A. Bochvar and E. G. Galpern made a quantum-chemical analysis of the stability of {{chem|C|60}} and calculated its electronic structure. The paper was published in 1973,<ref>{{Cite journal |last1=Bochvar |first1=D.A. |last2=Galpern |first2=E.G. |year=1973 |title=О гипотетических системах: карбододекаэдре, s-икосаэдре и карбо-s-икосаэдре |trans-title=On hypothetical systems: carbon dodecahedron, S-icosahedron and carbon-S-icosahedron |journal=[[Proceedings of the USSR Academy of Sciences|Dokl. Akad. Nauk SSSR]] |volume=209 |page=610}}</ref> but the scientific community did not give much importance to this theoretical prediction.

Around 1980, [[Sumio Iijima]] identified the molecule of {{chem|C|60}} from an electron microscope image of [[carbon black]], where it formed the core of a particle with the structure of a "bucky onion".<ref>{{Cite journal |last=Iijima |first=S |year=1980 |title=Direct observation of the tetrahedral bonding in graphitized carbon black by high resolution electron microscopy |journal=Journal of Crystal Growth |volume=50 |issue=3 |pages=675–683 |bibcode=1980JCrGr..50..675I |doi=10.1016/0022-0248(80)90013-5}}</ref>

Also in the 1980s at MIT, [[Mildred Dresselhaus]] and [[Morinobu Endo]], collaborating with T. Venkatesan, directed studies blasting graphite with lasers, producing carbon clusters of atoms, which would be later identified as "fullerenes."<ref>{{Cite web |date=2016-10-05 |title=Mildred S. Dresselhaus |url=https://www.fi.edu/laureates/mildred-s-dresselhaus |access-date=2022-10-08 |website=The Franklin Institute |language=en}}</ref>

===Discovery of {{chem|C|60}}===
In 1985, [[Harold Kroto]] of the [[University of Sussex]], working with [[James R. Heath]], [[Sean O'Brien (scientist)|Sean O'Brien]], [[Robert Curl]] and [[Richard Smalley]] from [[Rice University]], discovered fullerenes in the sooty residue created by vaporising carbon in a [[helium]] atmosphere. In the [[mass spectrometry|mass spectrum]] of the product, discrete peaks appeared corresponding to molecules with the exact mass of sixty or seventy or more carbon atoms, namely {{chem|C|60}} and {{chem|C|70}}. The team identified their structure as the now familiar "buckyballs".<ref name="kroto1985">{{Cite journal |last1=Kroto |first1=H.W. |last2=Heath, J. R. |last3=Obrien |first3=S. C. |last4=Curl |first4=R. F. |last5=Smalley |first5=R. E. |display-authors=3 |year=1985 |title={{chem|C|60}}: Buckminsterfullerene |journal=[[Nature (journal)|Nature]] |volume=318 |issue=6042 |pages=162–163 |bibcode=1985Natur.318..162K |doi=10.1038/318162a0 |s2cid=4314237}}</ref>

The name "buckminsterfullerene" was eventually chosen for {{chem|C|60}} by the discoverers as an homage to [[American people|American]] [[architect]] [[Buckminster Fuller]] for the vague similarity of the structure to the [[geodesic dome]]s which he popularized; which, if they were extended to a full sphere, would also have the icosahedral symmetry group.<ref>[http://www.chm.bris.ac.uk/motm/buckyball/c60a.htm Buckminsterfullerene, {{chem|C|60}}]. Sussex Fullerene Group. chm.bris.ac.uk</ref> The "ene" ending was chosen to indicate that the carbons are [[saturated hydrocarbon|unsaturated]], being connected to only three other atoms instead of the normal four. The shortened name "fullerene" eventually came to be applied to the whole family.

Kroto, Curl, and Smalley were awarded the 1996 [[Nobel Prize in Chemistry]]<ref>{{Cite web |title=The Nobel Prize in Chemistry 1996 |url=https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1996/ |access-date=7 February 2014}}</ref> for their roles in the discovery of this class of molecules.

===Further developments===
Kroto and the Rice team already discovered other fullerenes besides C<sub>60</sub>,<ref name=kroto1985/> and the list was much expanded in the following years. Carbon nanotubes [[Carbon nanotubes#Discovery|were first discovered and synthesized]] in 1991.<ref>{{Cite web |last=Mraz |first=S.J. |date=14 April 2005 |title=A new buckyball bounces into town |website=[[Machine Design]] |url=http://machinedesign.com/ContentItem/60618/Anewbuckyballbouncesintotown.aspx |archive-url=https://web.archive.org/web/20081013233853/http://machinedesign.com/ContentItem/60618/Anewbuckyballbouncesintotown.aspx |archive-date=13 October 2008}}</ref><ref>{{cite journal |last=Iijima |first=Sumio |title=Helical microtubules of graphitic carbon |journal=Nature |volume=354 |issue=6348 |pages=56–58 |year=1991 |bibcode=1991Natur.354...56I |doi=10.1038/354056a0 |s2cid=4302490}}</ref>

After their discovery, minute quantities of fullerenes were found to be produced in [[soot|sooty flames]],<ref>{{Cite journal |last1=Reilly |first1=P. T. A. |last2=Gieray |first2=R. A. |last3=Whitten |first3=W. B. |last4=Ramsey |first4=J. M. |date=2000 |title=Fullerene Evolution in Flame-Generated Soot |journal=Journal of the American Chemical Society |volume=122 |issue=47 |pages=11596–11601 |doi=10.1021/ja003521v |bibcode=2000JAChS.12211596R |issn=0002-7863}}</ref> and by [[lightning]] discharges in the atmosphere.<ref name=invWeb2010/> In 1992, fullerenes were found in a family of mineraloids known as [[shungite]]s in [[Karelia]], Russia.<ref name=buseck1992/>

The production techniques were improved by many scientists, including [[Donald Huffman]], [[Wolfgang Krätschmer]], [[Lowell D. Lamb]], and [[Konstantinos Fostiropoulos]].<ref>{{Cite journal |last1=Krätschmer |first1=W. |last2=Lamb |first2=Lowell D. |last3=Fostiropoulos |first3=K. |last4=Huffman |first4=Donald R. |date=1990 |title=Solid C60: a new form of carbon |url=http://www.nature.com/articles/347354a0 |journal=Nature |language=en |volume=347 |issue=6291 |pages=354–358 |bibcode=1990Natur.347..354K |doi=10.1038/347354a0 |issn=0028-0836 |s2cid=4359360|url-access=subscription }}</ref> Thanks to their efforts, by 1990 it was relatively easy to produce gram-sized samples of fullerene powder. [[Fullerene purification]] remains a challenge to chemists and to a large extent determines fullerene prices.

In 2010, the [[spectrum|spectral signatures]] of C<sub>60</sub> and C<sub>70</sub> were observed by NASA's [[Spitzer Space Telescope|Spitzer]] infrared telescope in a cloud of cosmic dust surrounding a star 6500 light years away.<ref name=cami2010/> Kroto commented: "This most exciting breakthrough provides convincing evidence that the buckyball has, as I long suspected, existed since time immemorial in the dark recesses of our galaxy."<ref name=bbc2010/> According to astronomer Letizia Stanghellini, "It's possible that buckyballs from outer space provided seeds for life on Earth."<ref>{{Cite news |last=Atkinson |first=Nancy |date=27 October 2010 |title=Buckyballs Could Be Plentiful in the Universe |work=[[Universe Today]] |url=http://www.universetoday.com/76732/buckyballs-could-be-plentiful-in-the-universe |access-date=28 October 2010}}</ref> In 2019, ionized C<sub>60</sub> molecules were detected with the [[Hubble Space Telescope]] in the space between those stars.<ref name="SA-20190429">{{Cite news |last=Starr |first=Michelle |date=29 April 2019 |title=The Hubble Space Telescope Has Just Found Solid Evidence of Interstellar Buckyballs |work=ScienceAlert.com |url=https://www.sciencealert.com/the-hubble-space-telescope-has-found-evidence-of-interstellar-buckyballs |access-date=29 April 2019}}</ref><ref name="AJL-20190422">{{Cite journal |last=Cordiner, M.A. |display-authors=et al. |date=22 April 2019 |title=Confirming Interstellar C60 + Using the Hubble Space Telescope |journal=[[The Astrophysical Journal Letters]] |volume=875 |pages=L28 |arxiv=1904.08821 |bibcode=2019ApJ...875L..28C |doi=10.3847/2041-8213/ab14e5 |number=2 |s2cid=121292704 |doi-access=free }}</ref>

==Types==
There are two major families of fullerenes, with fairly distinct properties and applications: the closed buckyballs and the open-ended cylindrical carbon nanotubes.<ref name="miess2004">{{Cite book |last1=Miessler |first1=G.L. |url=https://archive.org/details/inorganicchemist03edmies |title=Inorganic Chemistry |last2=Tarr |first2=D.A. |publisher=[[Pearson Education]] |year=2004 |isbn=978-0-13-120198-9 |edition=3rd |url-access=registration}}</ref> However, hybrid structures exist between those two classes, such as [[carbon nanobuds]] — nanotubes capped by [[wikt:hemisphere|hemispherical]] meshes or larger "buckybuds".

===Buckyballs===
[[Image:c60 isosurface.png|thumb|right|{{chem|C|60}} with [[isosurface]] of ground state electron density as calculated with [[density functional theory]] (DFT)]]
[[Image:C60 Buckyball.gif|thumb|right|Rotating view of {{chem|C|60}}, one kind of fullerene]]

====Buckminsterfullerene====
{{main|Buckminsterfullerene}}
Buckminsterfullerene is the smallest fullerene molecule containing pentagonal and hexagonal rings in which no two pentagons share an edge (which can be destabilizing, as in [[pentalene]]). It is also most common in terms of natural occurrence, as it can often be found in [[soot]].

The empirical formula of buckminsterfullerene is {{chem|C|60}} and its structure is a [[truncated icosahedron]], which resembles an [[Association football (ball)|association football ball]] of the type made of twenty(20) hexagons and twelve (12) 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 buckminsterfullerene molecule is about 1.1 [[nanometer]]s (nm).<ref>{{Cite journal |last1=Qiao |first1=Rui |last2=Roberts |first2=Aaron P. |last3=Mount |first3=Andrew S. |last4=Klaine |first4=Stephen J. |last5=Ke |first5=Pu Chun |display-authors=3 |year=2007 |title=Translocation of {{chem|C|60}} and Its Derivatives Across a Lipid Bilayer |journal=Nano Letters |volume=7 |issue=3 |pages=614–9 |bibcode=2007NanoL...7..614Q |citeseerx=10.1.1.725.7141 |doi=10.1021/nl062515f |pmid=17316055}}</ref> The nucleus to nucleus diameter of a buckminsterfullerene molecule is about 0.71&nbsp;nm.

The buckminsterfullerene molecule has two bond lengths. The 6:6 ring bonds (between two hexagons) can be considered "[[double bond]]s" and are shorter  (1.401 Å) than the 6:5 bonds (1.458 Å, between a hexagon and a pentagon). The weighted average bond length is 1.44 Å.<ref>{{Cite journal |last1=Hedberg |first1=Kenneth |last2=Hedberg |first2=Lise |last3=Bethune |first3=Donald S. |last4=Brown |first4=C. A. |last5=Dorn |first5=H. C. |last6=Johnson |first6=Robert D. |last7=De Vries |first7=M. |date=1991-10-18 |title=Bond Lengths in Free Molecules of Buckminsterfullerene, C 60, from Gas-Phase Electron Diffraction |url=https://www.science.org/doi/10.1126/science.254.5030.410 |journal=Science |language=en |volume=254 |issue=5030 |pages=410–412 |doi=10.1126/science.254.5030.410 |pmid=17742230 |issn=0036-8075|url-access=subscription }}</ref>

====Other fullerenes====
[[File:Fullerene_C70.png|thumb|{{chem|C|70}} has 10 additional atoms (shown in red) added to {{chem|C|60}} and a hemisphere rotated to fit]]
Another fairly common fullerene has empirical formula {{chem|C|70}},<ref>{{Cite web |last=Locke |first=W. |date=13 October 1996 |title=Buckminsterfullerene: Molecule of the Month |url=http://www.bristol.ac.uk/Depts/Chemistry/MOTM/buckyball/c60a.htm |access-date=4 July 2010 |publisher=[[Imperial College]]}}</ref> but fullerenes with 72, 76, 84 and even up to 100 carbon atoms are commonly obtained.

The smallest possible fullerene is the [[Dodecahedron|dodecahedral]] {{chem|C|20}}. There are no fullerenes with 22 vertices.<ref>{{Cite journal |last=Meija |first=Juris |year=2006 |title=Goldberg Variations Challenge |url=https://www.springer.com/cda/content/document/cda_downloaddocument.pdf?SGWID=0-0-45-275900-0 |journal=[[Analytical and Bioanalytical Chemistry]] |volume=385 |issue=1 |pages=6–7 |doi=10.1007/s00216-006-0358-9 |pmid=16598460 |s2cid=95413107}}</ref> The number of different fullerenes C<sub>2n</sub> grows with increasing ''n''&nbsp;=&nbsp;12,&nbsp;13,&nbsp;14,&nbsp;..., roughly in proportion to ''n''<sup>9</sup> {{OEIS|id=A007894}}. For instance, there are 1812 non-isomorphic fullerenes {{chem|C|60}}. Note that only one form of {{chem|C|60}}, buckminsterfullerene, has no pair of adjacent pentagons (the smallest such fullerene). To further illustrate the growth, there are 214,127,713 non-isomorphic fullerenes {{chem|C|200}}, 15,655,672 of which have no adjacent pentagons. Optimized structures of many fullerene isomers are published and listed on the web.<ref>Fowler, P. W. and Manolopoulos, D. E. [https://web.archive.org/web/20150109011908/http://www.nanotube.msu.edu/fullerene/fullerene-isomers.html {{chem|C|''n''}} Fullerenes]. nanotube.msu.edu</ref>

[[Heterofullerene]]s have heteroatoms substituting carbons in cage or tube-shaped structures. They were discovered in 1993<ref>Harris, D.J. "Discovery of Nitroballs: Research in Fullerene Chemistry" http://www.usc.edu/CSSF/History/1993/CatWin_S05.html {{Webarchive|url=https://web.archive.org/web/20151129202804/http://www.usc.edu/CSSF/History/1993/CatWin_S05.html |date=29 November 2015 }}</ref> and greatly expand the overall fullerene class of compounds and can have dangling bonds on their surfaces. Notable examples include boron, nitrogen ([[azafullerene]]), oxygen, and phosphorus derivatives.

===Carbon nanotubes===
[[Image:Kohlenstoffnanoroehre Animation.gif|frame|This rotating model of a [[carbon nanotube]] shows its 3D structure.]]
[[Carbon nanotubes]] are cylindrical fullerenes. These tubes of carbon are usually only a few nanometres wide, but they can range from less than a micrometer to several millimeters 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 [[Ultimate tensile strength|tensile strength]], high [[electrical conductivity]], high [[ductility]], high [[Thermal conductivity|heat conductivity]], and relative [[Chemically inert|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 battery|paper batteries]], developed in 2007 by researchers at [[Rensselaer Polytechnic Institute]].<ref>{{Cite journal |last1=Pushparaj |first1=V.L. |last2=Shaijumon, Manikoth M. |last3=Kumar |first3=A. |last4=Murugesan |first4=S. |last5=Ci |first5=L. |last6=Vajtai |first6=R. |last7=Linhardt |first7=R. J. |last8=Nalamasu |first8=O. |last9=Ajayan |first9=P. M. |display-authors=3 |year=2007 |title=Flexible energy storage devices based on nanocomposite paper |journal=[[Proceedings of the National Academy of Sciences]] |volume=104 |issue=34 |pages=13574–7 |bibcode=2007PNAS..10413574P |doi=10.1073/pnas.0706508104 |pmc=1959422 |pmid=17699622 |doi-access=free}}</ref> Another highly speculative proposed use in the field of space technologies is to produce high-tensile carbon cables required by a [[space elevator]].

==Derivatives==
Buckyballs and carbon nanotubes have been used as building blocks for a great variety of derivatives and larger structures, such as<ref name=miess2004/>
*Nested buckyballs ("carbon nano-onions" or "buckyonions")<ref>{{Cite journal |last=Ugarte |first=D. |year=1992 |title=Curling and closure of graphitic networks under electron-beam irradiation |journal=[[Nature (journal)|Nature]] |volume=359 |issue=6397 |pages=707–709 |bibcode=1992Natur.359..707U |doi=10.1038/359707a0 |pmid=11536508 |s2cid=2695746}}</ref> proposed for [[Lubricant|lubricants]];<ref>{{Cite journal |last1=Sano |first1=N. |last2=Wang, H. |last3=Chhowalla |first3=M. |last4=Alexandrou |first4=I. |last5=Amaratunga |first5=G. A. J. |display-authors=3 |year=2001 |title=Synthesis of carbon 'onions' in water |journal=[[Nature (journal)|Nature]] |volume=414 |issue=6863 |pages=506–7 |bibcode=2001Natur.414..506S |doi=10.1038/35107141 |pmid=11734841 |s2cid=4431690}}</ref>
*Nested carbon nanotubes ("carbon megatubes")<ref>{{Cite journal |last1=Mitchel |first1=D.R. |last2=Brown, R. Malcolm Jr. |year=2001 |title=The Synthesis of Megatubes: New Dimensions in Carbon Materials |journal=[[Inorganic Chemistry (journal)|Inorganic Chemistry]] |volume=40 |issue=12 |pages=2751–5 |doi=10.1021/ic000551q |pmid=11375691}}</ref>
*Linked "ball-and-chain" dimers (two buckyballs linked by a carbon chain)<ref>{{Cite journal |last1=Shvartsburg |first1=A.A. |last2=Hudgins, R. R. |last3=Gutierrez |first3=Rafael |last4=Jungnickel |first4=Gerd |last5=Frauenheim |first5=Thomas |last6=Jackson |first6=Koblar A. |last7=Jarrold |first7=Martin F. |display-authors=3 |year=1999 |title=Ball-and-Chain Dimers from a Hot Fullerene Plasma |url=http://www.indiana.edu/~nano/publications/1999/Ball_and_Chain_Dimers_from_a_Hot_Fullerene_Plasma.pdf |journal=[[Journal of Physical Chemistry A]] |volume=103 |issue=27 |pages=5275–5284 |bibcode=1999JPCA..103.5275S |doi=10.1021/jp9906379}}</ref>
*Rings of buckyballs linked together.<ref>{{Cite journal |last1=Li |first1=Y. |last2=Huang, Y. |last3=Du |first3=Shixuan |last4=Liu |first4=Ruozhuang |year=2001 |title=Structures and stabilities of {{chem|C|60}}-rings |journal=[[Chemical Physics Letters]] |volume=335 |issue=5–6 |pages=524–532 |bibcode=2001CPL...335..524L |doi=10.1016/S0009-2614(01)00064-1}}</ref>

==Heterofullerenes and non-carbon fullerenes==
After the discovery of C60, many fullerenes have been synthesized (or studied theoretically by [[molecular modeling]] methods) in which some or all the carbon atoms are replaced by other elements. [[Non-carbon nanotube]]s, in particular, have attracted much attention.

===Boron===
A type of buckyball which uses [[boron]] atoms, instead of the usual carbon, was predicted and described in 2007. The {{chem|B|80}} structure, with each atom forming 5 or 6 bonds, was predicted to be more stable than the {{chem|C|60}} buckyball.<ref>{{Cite journal |last1=Gonzalez Szwacki |first1=N. |last2=Sadrzadeh |first2=A. |last3=Yakobson |first3=B. |year=2007 |title={{chem|B|80}} Fullerene: An Ab Initio Prediction of Geometry, Stability, and Electronic Structure |journal=[[Physical Review Letters]] |volume=98 |issue=16 |article-number=166804 |bibcode=2007PhRvL..98p6804G |doi=10.1103/PhysRevLett.98.166804 |pmid=17501448}}</ref> However, subsequent analysis found that the predicted I<sub>h</sub> symmetric structure was vibrationally unstable and the resulting cage would undergo a spontaneous symmetry break, yielding a puckered cage with rare T<sub>h</sub> symmetry (symmetry of a [[volleyball (ball)|volleyball]]).<ref>{{Cite journal |last1=Gopakumar |first1=G. |last2=Nguyen |first2=M.T. |last3=Ceulemans |first3=A. |year=2008 |title=The boron buckyball has an unexpected Th symmetry |journal=[[Chemical Physics Letters]] |volume=450 |issue=4–6 |pages=175–177 |arxiv=0708.2331 |bibcode=2008CPL...450..175G |doi=10.1016/j.cplett.2007.11.030 |s2cid=97264790}}</ref> The number of six-member rings in this molecule is 20 and number of five-member rings is 12. There is an additional atom in the center of each six-member ring, bonded to each atom surrounding it. By employing a systematic global search algorithm, it was later found that the previously proposed {{chem|B|80}} fullerene is not a global maximum for 80-atom boron clusters and hence can not be found in nature; the most stable configurations have complex geometries.<ref name="de2011">{{Cite journal |last1=De |first1=S. |last2=Willand |first2=A. |last3=Amsler |first3=M. |last4=Pochet |first4=P. |last5=Genovese |first5=L. |last6=Goedecker |first6=S. |display-authors=3 |year=2011 |title=Energy Landscape of Fullerene Materials: A Comparison of Boron to Boron Nitride and Carbon |journal=Physical Review Letters |volume=106 |issue=22 |article-number=225502 |arxiv=1012.3076 |bibcode=2011PhRvL.106v5502D |doi=10.1103/PhysRevLett.106.225502 |pmid=21702613 |s2cid=16414023}}</ref> The same paper concluded that boron's energy landscape, unlike others, has many disordered low-energy structures, hence pure boron fullerenes are unlikely to exist in nature.<ref name=de2011/>

However, an irregular {{chem|B|40}} complex dubbed [[borospherene]] was prepared in 2014. This complex has two hexagonal faces and four heptagonal faces with in D<sub>2d</sub> symmetry interleaved with a network of 48 triangles.<ref>{{Cite journal |last1=Zhai |first1=Hua-Jin |last2=Ya-Fan Zhao |last3=Wei-Li Li |last4=Qiang Chen |last5=Hui Bai |last6=Han-Shi Hu |last7=Zachary A. Piazza |last8=Wen-Juan Tian |last9=Hai-Gang Lu |last10=Yan-Bo Wu |last11=Yue-Wen Mu |display-authors=3 |date=2014-07-13 |title=Observation of an all-boron fullerene |journal=Nature Chemistry |volume=6 |issue=8 |pages=727–731 |bibcode=2014NatCh...6..727Z |doi=10.1038/nchem.1999 |issn=1755-4349 |pmid=25054944 |author12=Guang-Feng Wei |author13=Zhi-Pan Liu |author14=Jun Li |author15=Si-Dian Li |author16=Lai-Sheng Wang}}</ref>

{{chem|B|80}} was experimentally obtained in 2024, i.e. 17 years after theoretical prediction by Gonzalez Szwacki ''et al.''.<ref>{{Cite journal |last1 = Choi |first1 = Hyun Wook |last2 = Zhang |first2 = Yang-Yang |last3 = Kahraman |first3 = Deniz |last4 = Xu |first4 = Cong-Qiao |last5 = Li |first5 = Jun |last6 = Wang |first6 = Lai-Sheng |title = Boron Buckminsterfullerene |year = 2024 |journal = ChemRxiv |doi = 10.26434/chemrxiv-2024-2xnxl|doi-access = free }}</ref>

===Other elements===
Inorganic (carbon-free) fullerene-type structures have been built with the [[molybdenum(IV) sulfide]] (MoS<sub>2</sub>), long used as a graphite-like lubricant, [[tungsten(IV) sulfide|tungsten (WS<sub>2</sub>)]], [[titanium(IV) sulfide|titanium (TiS<sub>2</sub>)]] and [[niobium(IV) sulfide|niobium (NbS<sub>2</sub>)]]. These materials were found to be stable up to at least 350 tons/cm<sup>2</sup> (34.3 [[gigapascal|GPa]]).<ref>{{Cite news |last1=Genuth |first1=Iddo |last2=Yaffe |first2=Tomer |date=February 15, 2006 |title=Protecting the soldiers of tomorrow |work=IsraCast |url=http://www.isracast.com/article.aspx?id=28 |archive-url=https://web.archive.org/web/20080326231723/http://www.isracast.com/article.aspx?id=28 |archive-date=March 26, 2008}}</ref>

Icosahedral or distorted-icosahedral fullerene-like complexes have also been prepared for [[germanium]], [[tin]], and [[lead]]; some of these complexes are spacious enough to hold most transition metal atoms.<ref>{{Cite journal |last1=Cui |first1=Li-Feng |last2=Xin Huang |last3=Lei-Ming Wang |last4=Dmitry Yu. Zubarev |last5=Alexander I. Boldyrev |last6=Jun Li |last7=Lai-Sheng Wang |display-authors=3 |date=2006-07-01 |title=Sn122-: Stannaspherene |journal=Journal of the American Chemical Society |volume=128 |issue=26 |pages=8390–8391 |doi=10.1021/ja062052f |issn=0002-7863 |pmid=16802791|bibcode=2006JAChS.128.8390C }}</ref><ref>{{Cite journal |last1=Cui |first1=Li-Feng |last2=Xin Huang |last3=Lei-Ming Wang |last4=Jun Li |last5=Lai-Sheng Wang |display-authors=3 |date=2006-08-01 |title=Pb122-: Plumbaspherene |journal=The Journal of Physical Chemistry A |volume=110 |issue=34 |pages=10169–10172 |bibcode=2006JPCA..11010169C |doi=10.1021/jp063617x |issn=1089-5639 |pmid=16928103}}</ref>
{{clear}}

==Main fullerenes==
Below is a table of main closed carbon fullerenes synthesized and characterized so far, with their [[Chemical Abstract Service|CAS]] number when known.<ref>{{Cite book |last1=W. L. F. Armarego |url=https://books.google.com/books?id=PTXyS7Yj6zUC&pg=PA214 |title=Purification of laboratory chemicals |last2=Christina Li Lin Chai |date=11 May 2009 |publisher=Butterworth-Heinemann |isbn=978-1-85617-567-8 |pages=214– |access-date=26 December 2011}}</ref> Fullerenes with fewer than 60 carbon atoms have been called "lower fullerenes",<ref>{{cite journal |last1=Sun |first1=Marc C. Nicklaus |last2=Rui-hua |first2=Xie |title=Structure, Stability, and NMR Properties of Lower Fullerenes C38−C50 and Azafullerene C44N6 |journal=J. Phys. Chem. |date=2005 |volume=109 |issue=20 |pages=4617–4622 |doi=10.1021/jp0450181|pmid=16833800 |bibcode=2005JPCA..109.4617S }}</ref> and those with more than 70 atoms "higher fullerenes".<ref>{{cite journal |last1=Thilgen |first1=Carlo |last2=Herrmann |first2=Andreas |last3=Diederich |first3=François |title=The Covalent Chemistry of Higher Fullerenes: C70 and Beyond |journal=Angewandte Chemie International Edition in English |date=14 November 1997 |volume=36 |issue=21 |pages=2268–2280 |doi=10.1002/anie.199722681}}</ref>
{|class="wikitable" style="text-align:center"
!Formula <!--!![[CAS number]]--> !! Num.<br/>Isom.[http://www.nanotube.msu.edu/fullerene/fullerene-isomers.html]||Mol.<br/>Symm.!! Cryst.<br/>Symm. !![[Space group]]!! No !! Pearson <br/>symbol!!''a'' (nm)!!''b'' (nm)!!''c'' (nm)!!β°!!''Z''!! ρ<br/>(g/cm<sup>3</sup>)
|-
|{{chem|C|20}}<!--||	           -->||1 || I<sub>h</sub> || || || || || || || || || ||
|-
|{{chem|link=Buckminsterfullerene|C|60}}<!--||	99685-96-8 -->||1 || I<sub>h</sub> || || || || || || || || || ||
|-
|[[C70 fullerene|{{chem|C|70}}]]<!--||	115383-22-7 -->||1|| D<sub>5h</sub> || || || || || || || || || ||
|-
|{{chem|C|72}}<!--|| -->||1 || D<sub>6h</sub> || || || || || || || || || ||
|-
|{{chem|C|74}}<!--|| -->||1 || D<sub>3h</sub> || || || || || || || || || ||
|-
| rowspan=2 | {{chem|C|76}}<!--||135113-15-4 -->
| rowspan=2 | 2 
| rowspan=2 | D<sub>2</sub>* 
| [[Monoclinic crystal system|Monoclinic]] ||P2<sub>1</sub> ||4 || mP2 || 1.102|| 1.108||1.768||108.10||2 || 1.48
|-
|            <!--|| -->[[Cubic crystal system|Cubic]] ||Fm{{overline|3}}m|| 225 ||cF4 || 1.5475|| 1.5475|| 1.5475||90||4 || 1.64
|-
|{{chem|C|78}}<!--||136316-32-0 -->||5 || D<sub>2v</sub> || || || || || || || || || ||
|-
|{{chem|C|80}}<!--|| -->||7|| || || || || || || || || || ||
|-
|{{chem|C|82}}<!--|| -->||9 ||{{chem|C|2}}, C<sub>2v</sub>, C<sub>3v</sub> || [[Monoclinic crystal system|Monoclinic]] ||P2<sub>1</sub> ||4 || mP2 || 1.141 || 1.1355 ||1.8355||108.07||2 ||
|-
|{{chem|C|84}}<!--||135113-16-5 -->||24 || D<sub>2</sub>*, D<sub>2d</sub>|| [[Cubic crystal system|Cubic]] ||Fm{{overline|3}}m || || || 1.5817<ref>{{Cite journal |last1=Margadonna |first1=Serena |last2=Brown |first2=Craig M. |last3=Dennis |first3=T. John S. |last4=Lappas |first4=Alexandros |last5=Pattison |first5=Philip |last6=Prassides |first6=Kosmas |last7=Shinohara |first7=Hisanori |display-authors=3 |date=July 1998 |title=Crystal Structure of the Higher Fullerene C |journal=Chemistry of Materials |volume=10 |issue=7 |pages=1742–1744 |doi=10.1021/cm980183c}}</ref> || 1.5817 ||1.5817||90|| ||
|-
|{{chem|C|86}}<!--|| -->||19 || || || || || || || || || || ||
|-
|{{chem|C|88}}<!--|| -->||35 || || || || || || || || || || ||
|-
|{{chem|C|90}}<!--|| -->||46|| || || || || || || || || || ||
|-
|{{chem|C|3996}}<!--||175833-78-0-->|| || || || || || || || || || || ||
|}

In the table, "Num.Isom." is the number of possible [[isomer]]s within the "isolated pentagon rule", which states that two pentagons in a fullerene should not share edges.<ref>{{Cite journal |last1=Manolopoulos |first1=David E. |last2=Fowler |first2=Patrick W. |year=1991 |title=Structural proposals for endohedral metal-fullerene complexes |journal=Chemical Physics Letters |volume=187 |issue=1–2 |pages=1–7 |bibcode=1991CPL...187....1M |doi=10.1016/0009-2614(91)90475-O}}</ref><ref name="died1992">{{Cite journal |last1=Diederich |first1=Francois |last2=Whetten |first2=Robert L. |year=1992 |title=Beyond C60: The higher fullerenes |journal=Accounts of Chemical Research |volume=25 |issue=3 |page=119 |doi=10.1021/ar00015a004}}</ref> "Mol.Symm." is the symmetry of the molecule,<ref name=died1992/><ref>{{Cite book |last=K Veera Reddy |url=https://books.google.com/books?id=oZeFG6QDNekC&pg=PA126 |title=Symmetry And Spectroscopy Of Molecules |date=1 January 1998 |publisher=New Age International |isbn=978-81-224-1142-3 |pages=126– |access-date=26 December 2011}}</ref> whereas "Cryst.Symm." is that of the crystalline framework in the solid state. Both are specified for the most experimentally abundant form(s). The asterisk <nowiki>*</nowiki> marks symmetries with more than one chiral form.

When {{chem|C|76}} or {{chem|C|82}} crystals are grown from toluene solution they have a monoclinic symmetry. The crystal structure contains toluene molecules packed between the spheres of the fullerene. However, evaporation of the solvent from {{chem|C|76}} transforms it into a face-centered cubic form.<ref>{{Cite journal |last1=Kawada |first1=H. |last2=Fujii |first2=Y. |last3=Nakao |first3=H. |last4=Murakami |first4=Y. |last5=Watanuki |first5=T. |last6=Suematsu |first6=H. |last7=Kikuchi |first7=K. |last8=Achiba |first8=Y. |last9=Ikemoto |first9=I. |display-authors=3 |year=1995 |title=Structural aspects of {{chem|C|82}} and {{chem|C|76}} crystals studied by x-ray diffraction |journal=Physical Review B |volume=51 |issue=14 |pages=8723–8730 |doi=10.1103/PhysRevB.51.8723 |pmid=9977506}}</ref> Both monoclinic and [[face-centered cubic]] (fcc) phases are known for better-characterized [[buckminsterfullerene|{{chem|C|60}}]] and [[C70 fullerene|{{chem|C|70}}]] fullerenes.

==Properties==

===Topology===
[[Schlegel diagram]]s are often used to clarify the 3D structure of closed-shell fullerenes, as 2D projections are often not ideal in this sense.<ref name="iupacful">{{Cite journal |last1=Powell |first1=W. H. |last2=Cozzi |first2=F. |last3=Moss |first3=G. P. |last4=Thilgen |first4=C. |last5=Hwu |first5=R. J.-R. |last6=Yerin |first6=A. |display-authors=3 |date=2002 |title=Nomenclature for the C60-Ih and C70-D5h(6) Fullerenes (IUPAC Recommendations 2002) |url=http://doc.rero.ch/record/303076/files/pac200274040629.pdf |journal=Pure and Applied Chemistry |volume=74 |issue=4 |pages=629–695 |doi=10.1351/pac200274040629 |s2cid=93423610}}</ref>

In mathematical terms, the [[combinatorial topology]] (that is, the carbon atoms and the bonds between them, ignoring their positions and distances) of a closed-shell fullerene with a simple sphere-like mean surface ([[Orientability|orientable]], [[genus (topology)|genus]] zero) can be represented as a convex [[polyhedron]]; more precisely, its [[dimension (mathematics)|one-dimensional]] skeleton, consisting of its vertices and edges. The Schlegel diagram is a projection of that skeleton onto one of the faces of the polyhedron, through a point just outside that face; so that all other vertices project inside that face.
<gallery widths="160px" heights="160px" style="text-align:center;" caption="Schlegel diagrams of some fullerenes">
Graph of 20-fullerene w-nodes.svg|C20<br />([[dodecahedron]])
Graph of 26-fullerene 5-base w-nodes.svg|C26
Graph of 60-fullerene w-nodes.svg|C60<br/>([[truncated icosahedron]])
Graph of 70-fullerene w-nodes.svg|C70
</gallery>
The Schlegel diagram of a closed fullerene is a [[graph theory|graph]] that is [[planar graph|planar]] and [[regular graph|3-regular]] (or "cubic"; meaning that all vertices have [[degree (graph theory)|degree]] 3).

A closed fullerene with sphere-like shell must have at least some cycles that are pentagons or heptagons. More precisely, if all the faces have 5 or 6 sides, it follows from [[Euler characteristic|Euler's polyhedron formula]], ''V''−''E''+''F''=2 (where ''V'', ''E'', ''F'' are the numbers of vertices, edges, and faces), that ''V'' must be even, and that there must be exactly 12 pentagons and ''V''/2−10 hexagons. Similar constraints exist if the fullerene has heptagonal (seven-atom) cycles.<ref>[https://www.britannica.com/EBchecked/topic/221916/fullerene "Fullerene"], ''Encyclopædia Britannica'' on-line</ref>

===Bonding===
Since each carbon atom is connected to only three neighbors, instead of the usual four, it is customary to describe those bonds as being a mixture of [[single bond|single]] and [[double bond|double]] [[covalent bond]]s.<!--delocalized bonding, resonance--> The hybridization of carbon in C<sub>60</sub> has been reported to be sp<sup>2.01</sup>.<ref name="Yamada">{{Cite journal |last1=Diana |first1=Nooramalina |last2=Yamada |first2=Yasuhiro |last3=Gohda |first3=Syun |last4=Ono |first4=Hironobu |last5=Kubo |first5=Shingo |last6=Sato |first6=Satoshi |display-authors=3 |date=2021-02-01 |title=Carbon materials with high pentagon density |journal=Journal of Materials Science |language=en |volume=56 |issue=4 |pages=2912–2943 |bibcode=2021JMatS..56.2912D |doi=10.1007/s10853-020-05392-x |issn=1573-4803 |s2cid=224784081}}</ref> The bonding state can be analyzed by [[Raman spectroscopy]], [[IR spectroscopy]] and [[X-ray photoelectron spectroscopy]].<ref name=Yamada/><ref>{{Cite journal |last1=Kim |first1=Jungpil |last2=Yamada |first2=Yasuhiro |last3=Kawai |first3=Miki |last4=Tanabe |first4=Takehiro |last5=Sato |first5=Satoshi |display-authors=3 |date=2015-10-01 |title=Spectral change of simulated X-ray photoelectron spectroscopy from graphene to fullerene |journal=Journal of Materials Science |language=en |volume=50 |issue=20 |pages=6739–6747 |bibcode=2015JMatS..50.6739K |doi=10.1007/s10853-015-9229-0 |issn=1573-4803 |s2cid=93478144}}</ref>

===Encapsulation===
{{Main|Endohedral fullerenes}}

Additional atoms, ions, clusters, or small molecules can be trapped inside fullerenes to form [[inclusion compound]]s known as [[endohedral fullerenes]]. An unusual example is the egg-shaped fullerene Tb<sub>3</sub>N@{{chem|C|84}}, which violates the isolated pentagon rule.<ref>{{Cite journal |last1=Beavers |first1=C.M. |last2=Zuo, T. |year=2006 |title=Tb<sub>3</sub>N@{{chem|C|84}}: An improbable, egg-shaped endohedral fullerene that violates the isolated pentagon rule |journal=[[Journal of the American Chemical Society]] |volume=128 |issue=35 |pages=11352–3 |doi=10.1021/ja063636k |pmid=16939248|bibcode=2006JAChS.12811352B }}</ref> Evidence for a meteor impact at the end of the [[Permian]] period was found by analyzing [[noble gas]]es preserved by being trapped in fullerenes.<ref>{{Cite journal |last1=Luann |first1=B. |last2=Poreda, Robert J. |last3=Hunt |first3=Andrew G. |last4=Bunch |first4=Theodore E. |last5=Rampino |first5=Michael |display-authors=3 |year=2007 |title=Impact Event at the Permian-Triassic Boundary: Evidence from Extraterrestrial Noble Gases in Fullerenes |journal=[[Science (journal)|Science]] |volume=291 |issue=5508 |pages=1530–3 |bibcode=2001Sci...291.1530B |doi=10.1126/science.1057243 |pmid=11222855 |s2cid=45230096}}</ref>

===Research===
In the field of [[nanotechnology]], [[thermal conductivity|heat resistance]] and [[superconductivity]] are some of the more heavily studied properties.

There are many calculations that have been done using [[ab-initio]] quantum methods applied to fullerenes. By [[Density functional theory|DFT]] and [[Time-dependent density functional theory|TD-DFT]] methods one can obtain [[Infra-red spectroscopy|IR]], [[Raman spectroscopy|Raman]] and [[Ultraviolet-visible spectroscopy|UV]] spectra. Results of such calculations can be compared with experimental results.

Fullerene is an unusual reactant in many [[organic reaction]]s such as the [[Bingel reaction]] discovered in 1993.

===Aromaticity===
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 [[Delocalized electron|delocalize]] over the whole molecule.

A spherical fullerene of ''n'' carbon atoms has ''n'' [[pi-bond]]ing electrons, free to delocalize. These should try to delocalize over the whole molecule. The quantum mechanics of such an arrangement should be like only one shell 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 number]]), but this series does not include 60. This 2(''N''&nbsp;+&nbsp;1)<sup>2</sup> rule (with ''N'' integer) for [[spherical aromaticity]] is the three-dimensional analogue of [[Hückel's rule]]. The 10+ [[cation]] would satisfy this rule, and should be aromatic. This has been shown to be the case using [[quantum chemical]] modelling, which showed the existence of strong diamagnetic sphere currents in the cation.<ref>{{Cite journal |last1=Johansson |first1=M.P. |last2=Jusélius |first2=J. |last3=Sundholm |first3=D. |year=2005 |title=Sphere Currents of Buckminsterfullerene |journal=[[Angewandte Chemie International Edition]] |volume=44 |issue=12 |pages=1843–6 |doi=10.1002/anie.200462348 |pmid=15706578}}</ref>

As a result, {{chem|C|60}} in water tends to pick up two more electrons and become an [[anion]]. The ''n''{{chem|C|60}} described below may be the result of {{chem|C|60}} trying to form a loose [[metallic bond]].

==Reactions==

===Polymerization===
Under high pressure and temperature, buckyballs collapse to form various one-, two-, or three-dimensional carbon frameworks. Single-strand polymers are formed using the [[Atom Transfer Radical Addition Polymerization]] (ATRAP) route.<ref>{{Cite journal |last1=Hiorns |first1=R.C. |last2=Cloutet, Eric |last3=Ibarboure |first3=Emmanuel |last4=Khoukh |first4=Abdel |last5=Bejbouji |first5=Habiba |last6=Vignau |first6=Laurence |last7=Cramail |first7=Henri |display-authors=3 |year=2010 |title=Synthesis of Donor-Acceptor Multiblock Copolymers Incorporating Fullerene Backbone Repeat Units |journal=Macromolecules |series=14 |volume=43 |issue=14 |pages=6033–6044 |bibcode=2010MaMol..43.6033H |doi=10.1021/ma100694y}}</ref>

[[Aggregated diamond nanorod|"Ultrahard fullerite"]] is a coined term frequently used to describe material produced by high-pressure high-temperature (HPHT) processing of fullerite. Such treatment converts fullerite into a nanocrystalline form of [[diamond]] which has been reported to exhibit remarkable mechanical properties.<ref>{{Cite journal |last1=Blank |first1=V. |last2=Popov |first2=M. |last3=Pivovarov |first3=G. |last4=Lvova |first4=N. |last5=Gogolinsky |first5=K. |last6=Reshetov |first6=V. |display-authors=3 |year=1998 |title=Ultrahard and superhard phases of fullerite {{chem|C|60}}: Comparison with diamond on hardness and wear |journal=Diamond and Related Materials |volume=7 |issue=2–5 |pages=427–431 |bibcode=1998DRM.....7..427B |citeseerx=10.1.1.520.7265 |doi=10.1016/S0925-9635(97)00232-X}}</ref>
[[Image:C60 SEM.jpg|thumb|Fullerite ([[scanning electron microscope]] image)]]

===Chemistry===
{{Main|Fullerene chemistry}}

Fullerenes are stable, but not totally unreactive. The sp<sup>2</sup>-hybridized carbon atoms, which are at their energy minimum in planar [[graphite#Structure|graphite]], must be bent to form the closed sphere or tube, which produces [[Ring strain|angle strain]]. The characteristic reaction of fullerenes is [[electrophilic addition]] at 6,6-double bonds, which reduces angle strain by changing sp<sup>2</sup>-hybridized carbons into sp<sup>3</sup>-hybridized ones. The change in hybridized [[atomic orbital|orbital]]s causes the bond angles to decrease from about 120° in the sp<sup>2</sup> orbitals to about 109.5° in the sp<sup>3</sup> 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.

===Solubility===
{{main|Fullerene solubility}}
[[File:C60 Fullerene solution.jpg|thumb|{{chem|C|60}} in solution]]

[[File:Carbon 60 Olive Oil Solution.JPG|thumb|{{chem|C|60}} in extra virgin olive oil, showing the characteristic purple color of pristine {{chem|C|60}} solutions]]

Fullerenes are soluble in many organic [[solvent]]s, such as [[toluene]], [[chlorobenzene]], and [[1,2,3-trichloropropane]]. Solubilities are generally rather low, such as 8 g/L for C<sub>60</sub> in [[carbon disulfide]]. Still, fullerenes are the only known [[allotrope]] of carbon that can be dissolved in common solvents at room temperature.<ref>{{Cite journal |last1=Beck |first1=Mihály T. |last2=Mándi |first2=Géza |year=1997 |title=Solubility of {{chem|C|60}} |journal=Fullerenes, Nanotubes and Carbon Nanostructures |volume=5 |issue=2 |pages=291–310 |doi=10.1080/15363839708011993}}</ref><ref>{{Cite journal |last1=Bezmel'nitsyn |first1=V.N. |last2=Eletskii |first2=A.V. |last3=Okun' |first3=M.V. |year=1998 |title=Fullerenes in solutions |journal=[[Physics-Uspekhi]] |volume=41 |issue=11 |pages=1091–1114 |bibcode=1998PhyU...41.1091B |doi=10.1070/PU1998v041n11ABEH000502 |s2cid=250785669}}</ref><ref>{{Cite journal |last1=Ruoff |first1=R.S. |last2=Tse, Doris S. |last3=Malhotra |first3=Ripudaman |last4=Lorents |first4=Donald C. |year=1993 |title=Solubility of fullerene ({{chem|C|60}}) in a variety of solvents |url=http://bucky-central.me.utexas.edu/RuoffsPDFs/40.pdf |journal=[[Journal of Physical Chemistry]] |volume=97 |issue=13 |pages=3379–3383 |doi=10.1021/j100115a049 |archive-url=https://web.archive.org/web/20120508111820/http://bucky-central.me.utexas.edu/RuoffsPDFs/40.pdf |archive-date=8 May 2012 |access-date=24 February 2015}}</ref><ref>{{Cite journal |last1=Sivaraman |first1=N. |last2=Dhamodaran |first2=R. |last3=Kaliappan |first3=I. |last4=Srinivasan |first4=T. G. |last5=Vasudeva Rao |first5=P. R. P. |last6=Mathews |first6=C. K. C. |display-authors=3 |year=1994 |title=Solubility of {{chem|C|70}} in Organic Solvents |journal=Fullerene Science and Technology |volume=2 |issue=3 |pages=233–246 |doi=10.1080/15363839408009549}}</ref><ref>{{Cite journal |last1=Semenov |first1=K. N. |last2=Charykov |first2=N. A. |last3=Keskinov |first3=V. A. |last4=Piartman |first4=A. K. |last5=Blokhin |first5=A. A. |last6=Kopyrin |first6=A. A. |display-authors=3 |year=2010 |title=Solubility of Light Fullerenes in Organic Solvents |journal=Journal of Chemical & Engineering Data |volume=55 |pages=13–36 |doi=10.1021/je900296s}}</ref> Among the best solvents is [[1-chloronaphthalene]], which will dissolve 51 g/L of C<sub>60</sub>.

Solutions of pure buckminsterfullerene have a deep purple color. Solutions of {{chem|C|70}} are a reddish brown. The [[higher fullerenes]] {{chem|C|76}} to {{chem|C|84}} have a variety of colors.

Millimeter-sized crystals of {{chem|C|60}} and {{chem|C|70}}, both pure and solvated, can be grown from benzene solution. Crystallization of {{chem|C|60}} from benzene solution below 30&nbsp;°C (when solubility is maximum) yields a [[triclinic]] solid [[solvate]] {{chem|C|60}}·4{{chem|C|6|H|6}}. Above 30&nbsp;°C one obtains solvate-free [[face-centered cubic|fcc]] {{chem|C|60}}.<ref>{{Cite journal |last=Talyzin |first=A.V. |year=1997 |title=Phase Transition {{chem|C|60}}−{{chem|C|60}}*4{{chem|C|6|H|6}} in Liquid Benzene |journal=[[Journal of Physical Chemistry B]] |volume=101 |issue=47 |pages=9679–9681 |doi=10.1021/jp9720303}}</ref><ref>{{Cite journal |last1=Talyzin |first1=A.V. |last2=Engström |first2=I. |year=1998 |title={{chem|C|70}} in Benzene, Hexane, and Toluene Solutions |journal=[[Journal of Physical Chemistry B]] |volume=102 |issue=34 |pages=6477–6481 |doi=10.1021/jp9815255}}</ref>

===Quantum mechanics===
In 1999, researchers from the [[University of Vienna]] demonstrated that [[wave-particle duality]] applied to molecules such as fullerene.<ref>{{Cite journal |last1=Arndt |first1=M. |last2=Nairz, Olaf |last3=Vos-Andreae |first3=Julian |last4=Keller |first4=Claudia |last5=Van Der Zouw |first5=Gerbrand |last6=Zeilinger |first6=Anton |display-authors=3 |year=1999 |title=Wave-particle duality of {{chem|C|60}} |url=http://www.qudev.ethz.ch/phys4/studentspresentations/waveparticle/arndt_c60molecules.pdf |journal=[[Nature (journal)|Nature]] |volume=401 |issue=6754 |pages=680–2 |bibcode=1999Natur.401..680A |doi=10.1038/44348 |pmid=18494170 |s2cid=4424892}}</ref>

===Superconductivity===
{{main|Buckminsterfullerene}}
Fullerenes are normally electrical insulators, but when crystallized with alkali metals, the resultant compound can be conducting or even superconducting.<ref>{{Cite book |last=Katz, E. A. |title=Nanostructured materials for solar energy conversion |publisher=Elsevier |year=2006 |isbn=978-0-444-52844-5 |editor-last=Sōga, Tetsuo |pages=372, 381 |chapter=Fullerene Thin Films as Photovoltaic Material |chapter-url=https://books.google.com/books?id=GmQR1tuk5IgC&pg=PA361}}</ref>

===Chirality===
Some fullerenes (e.g. {{chem|C|76}}, {{chem|C|78}}, {{chem|C|80}}, and {{chem|C|84}}) are [[inherent chirality|inherently chiral]] because they are D<sub>2</sub>-symmetric, and have been successfully resolved. Research efforts are ongoing to develop specific sensors for their enantiomers.

===Stability===
Two theories have been proposed to describe the molecular mechanisms that make fullerenes. The older, "bottom-up" theory proposes that they are built atom-by-atom. The alternative "top-down" approach claims that fullerenes form when much larger structures break into constituent parts.<ref name="kurz">[http://www.kurzweilai.net/support-for-top-down-theory-of-how-buckyballs-form Support for top-down theory of how 'buckyballs' form]. kurzweilai.net. 24 September 2013</ref>

In 2013 researchers discovered that asymmetrical fullerenes formed from larger structures settle into stable fullerenes. The synthesized substance was a particular [[metallofullerene]] consisting of 84 carbon atoms with two additional carbon atoms and two [[yttrium]] atoms inside the cage. The process produced approximately 100 micrograms.<ref name=kurz/>

However, they found that the asymmetrical molecule could theoretically collapse to form nearly every known fullerene and metallofullerene. Minor perturbations involving the breaking of a few molecular bonds cause the cage to become highly symmetrical and stable. This insight supports the theory that fullerenes can be formed from graphene when the appropriate molecular bonds are severed.<ref name=kurz/><ref>{{Cite journal |last1=Zhang |first1=J. |last2=Bowles |first2=F. L. |last3=Bearden |first3=D. W. |last4=Ray |first4=W. K. |last5=Fuhrer |first5=T. |last6=Ye |first6=Y. |last7=Dixon |first7=C. |last8=Harich |first8=K. |last9=Helm |first9=R. F. |last10=Olmstead |first10=M. M. |last11=Balch |first11=A. L. |display-authors=3 |year=2013 |title=A missing link in the transformation from asymmetric to symmetric metallofullerene cages implies a top-down fullerene formation mechanism |journal=Nature Chemistry |volume=5 |issue=10 |pages=880–885 |bibcode=2013NatCh...5..880Z |doi=10.1038/nchem.1748 |pmid=24056346 |last12=Dorn |first12=H. C.}}</ref>

==Systematic naming==
According to the [[IUPAC nomenclature of organic chemistry|IUPAC]], to name a fullerene, one must cite the number of member atoms for the rings which comprise the fullerene, its [[symmetry point group]] in the [[Schoenflies notation]], and the total number of atoms. For example, buckminsterfullerene C<sub>60</sub> is systematically named ({{chem|C|60}}-''I''<sub>h</sub>)[5,6]fullerene. The name of the point group should be retained in any derivative of said fullerene, even if that symmetry is lost by the derivation.

To indicate the position of substituted or attached elements, the fullerene atoms are usually numbered in a spiral path, usually starting with the ring on one of the main axes. If the structure of the fullerene does not allow such numbering, another starting atom was chosen to still achieve a spiral path sequence.

The latter is the case for C<sub>70</sub>, which is ({{chem|C|70}}-''D''<sub>5h(6)</sub>)[5,6]fullerene in IUPAC notation. The symmetry ''D''<sub>5h(6)</sub> means that this is the isomer where the ''C''<sub>5</sub> axis goes through a pentagon surrounded by hexagons rather than pentagons.<ref name=iupacful/>
<gallery widths="200px" heights="200px">
Buckminsterfullerene-2D-skeletal numbered.svg|({{chem|C|60}}-''I''h)[5,6]fullerene<br/>Carbon numbering. 
C70fullerene-2D-skeletal numbered.svg|({{chem|C|70}}-''D''<sub>5h(6)</sub>)[5,6]fullerene<br/>Carbon numbering.
C70fullerene-2D-skeletal numbered isobonds.svg|({{chem|C|70}}-''D''<sub>5h(6)</sub>)[5,6]fullerene<br/>Non-equivalent bonds shown by different colours.
Cyclopropa12 C70fullerene-2D-skeletal renumbered.svg|3'''H''-Cyclopropa[1,2]({{chem|C|70}}-''D''<sub>5h(6)</sub>)[5,6]fullerene.
Cyclopropa212 C70fullerene-2D-skeletal renumbered.svg|3'''H''-Cyclopropa[2,12]({{chem|C|70}}-''D''<sub>5h(6)</sub>)[5,6]fullerene.
PC71BM.svg|{{chem|C|71}}-PCBM, [1,2]-isomer.<br/>IUPAC name is methyl 4-(3'-phenyl-3'H-cyclopropa[1,2]({{chem|C|70}}-''D''<sub>5h(6)</sub>)[5,6]fullerene-3'-yl)butyrate.
</gallery>
In IUPAC's nomenclature, fully saturated analogues of fullerenes are called ''fulleranes''. If the mesh has [[heteroatom|other element(s)]] substituted for one or more carbons, the compound is named a ''heterofullerene''. If a double bond is replaced by a [[methylene bridge]] {{chem2|\sCH2\s}}, the resulting structure is a ''homofullerene''. If an atom is fully deleted and missing valences saturated with hydrogen atoms, it is a ''norfullerene''. When bonds are removed (both sigma and pi), the compound becomes ''secofullerene''; if some new bonds are added in an unconventional order, it is a ''cyclofullerene''.<ref name="iupacful" />

==Production==
Fullerene production generally starts by producing fullerene-rich soot. The original (and still current) method was to send a large electric current between two nearby [[graphite]] electrodes in an [[inert gas|inert]] atmosphere. The resulting [[electric arc]] vaporizes the carbon into a [[plasma (physics)|plasma]] that then cools into sooty residue.<ref name=kroto1985/> Alternatively, soot is produced by [[laser ablation]] of graphite or [[pyrolysis]] of [[aromatic hydrocarbon]]s.<ref>{{Cite web |last=Bobrowsky |first=Maciej |date=2019-10-01 |title=Nanostructures and computer simulations in material science |url=http://www.mif.pg.gda.pl/homepages/mate/Nanochemistry/nanochem_lect_10.pdf |access-date=2020-02-03}}</ref>{{citation needed|date=April 2019}} Combustion of benzene is the most efficient process, developed at [[Massachusetts Institute of Technology|MIT]].<ref>{{Cite book |last=Osawa, Eiji |url=https://books.google.com/books?id=8GjOboiuVW0C&pg=PA29 |title=Perspectives of Fullerene Nanotechnology |publisher=Springer Science & Business Media |year=2002 |isbn=978-0-7923-7174-8 |page=29}}</ref><ref name="arika2006">{{Cite journal |last=Arikawa |first=Mineyuki |year=2006 |title=Fullerenes—an attractive nano carbon material and its production technology. |journal=Nanotechnology Perceptions |volume=2 |issue=3 |pages=121–128 |issn=1660-6795}}</ref>

These processes yield a mixture of various fullerenes and other forms of carbon. The fullerenes are then extracted from the soot using [[solubility of fullerenes|appropriate organic solvents]] and separated by [[chromatography]].<ref>{{Cite book |last=Katz, E. A. |title=Nanostructured materials for solar energy conversion |publisher=Elsevier |year=2006 |isbn=978-0-444-52844-5 |editor-last=Sōga, Tetsuo |pages=361–443 |chapter=Fullerene Thin Films as Photovoltaic Material |doi=10.1016/B978-044452844-5/50014-7 |chapter-url=https://books.google.com/books?id=GmQR1tuk5IgC&pg=PA361}}</ref>{{rp|p.369}} One can obtain milligram quantities of fullerenes with 80 atoms or more. C<sub>76</sub>, C<sub>78</sub> and C<sub>84</sub> are available commercially.

==Applications==

===Biomedical===
Functionalized fullerenes have been researched extensively for several potential biomedical applications including high-performance MRI [[contrast agent]]s, X-ray imaging contrast agents, [[photodynamic therapy]] for tumor treatment,<ref>{{Cite journal |last1=Hu, Zhen |last2=Zhang |first2=Chunhua |last3=Huang |first3=Yudong |last4=Sun |first4=Shaofan |last5=Guan |first5=Wenchao |last6=Yao |first6=Yuhuan |display-authors=3 |year=2012 |title=Photodynamic anticancer activities of water-soluble {{chem|C|60}} derivatives and their biological consequences in a HeLa cell line |journal=Chemico-Biological Interactions |volume=195 |issue=1 |pages=86–94 |doi=10.1016/j.cbi.2011.11.003 |pmid=22108244}}</ref><ref>{{Cite journal |last1=Mroz, Pawel |last2=Pawlak |first2=Anna |last3=Satti |first3=Minahil |last4=Lee |first4=Haeryeon |last5=Wharton |first5=Tim |last6=Gali |first6=Hariprasad |last7=Sarna |first7=Tadeusz |last8=Hamblin |first8=Michael R. |display-authors=3 |year=2007 |title=Functionalized fullerenes mediate photodynamic killing of cancer cells: type I versus type II photochemical mechanism |journal=Free Radical Biology & Medicine |volume=43 |issue=5 |pages=711–719 |doi=10.1016/j.freeradbiomed.2007.05.005 |pmc=1995806 |pmid=17664135}}</ref> and drug and gene delivery.<ref name="lalwa2013">{{Cite journal |last1=Lalwani |first1=Gaurav |last2=Sitharaman |first2=Balaji |date=September 2013 |title=Multifunctional Fullerene- and Metallofullerene-Based Nanobiomaterials |url=https://www.worldscientific.com/doi/abs/10.1142/S1793984413420038 |journal=Nano LIFE |language=en |volume=03 |issue=3 |page=1342003 |doi=10.1142/S1793984413420038 |issn=1793-9844|url-access=subscription }}</ref><ref name="Pesado-Gómez 2024">{{cite journal | last1=Pesado-Gómez | first1=Casandra | last2=Serrano-García | first2=Juan S. | last3=Amaya-Flórez | first3=Andrés | last4=Pesado-Gómez | first4=Gustavo | last5=Soto-Contreras | first5=Anell | last6=Morales-Morales | first6=David | last7=Colorado-Peralta | first7=Raúl | title=Fullerenes: Historical background, novel biological activities versus possible health risks | journal=Coordination Chemistry Reviews | volume=501 | date=2024 | doi=10.1016/j.ccr.2023.215550 | article-number=215550}}</ref>

==Safety and toxicity==
{{Main|Health and safety hazards of nanomaterials| Toxicology of carbon nanomaterials}}
In 2013, a comprehensive review on the toxicity of fullerene was published reviewing work beginning in the early 1990s to present and concluded that very little evidence gathered since the discovery of fullerenes indicate that {{chem|C|60}} is toxic.<ref name=lalwa2013/> The toxicity of these carbon [[nanoparticle]]s is not only dose- and time-dependent, but also depends on a number of other factors such as:

* type (e.g.: {{chem|C|60}}, {{chem|C|70}}, M@{{chem|C|60}}, M@{{chem|C|82}})
* functional groups used to water-solubilize these nanoparticles (e.g.: OH, COOH)
* method of administration (e.g.: intravenous, intraperitoneal)

It was recommended to assess the pharmacology of every new fullerene- or metallofullerene-based complex individually as a different compound.

==Popular culture==
Examples of fullerenes appear frequently in [[popular culture]]. Fullerenes appeared in fiction well before scientists took serious interest in them. In a humorously speculative 1966 column for ''[[New Scientist]]'', [[David E. H. Jones|David Jones]] suggested the possibility of making giant hollow carbon molecules by distorting a plane hexagonal net with the addition of impurity atoms.<ref>{{Cite journal |last=Jones |first=D. |year=1966 |title=Note in Ariadne column |journal=[[New Scientist]] |volume=32 |page=245}}</ref>

==See also==
{{Div col|small=yes}}
*[[Buckypaper]]
*[[Carbocatalysis]]
*[[Dodecahedrane]]
*[[Fullerene ligand]]
*[[Goldberg–Coxeter construction]]
*[[Graphene]]
*[[Lonsdaleite]]
*[[Triumphene]]
*[[Truncated rhombic triacontahedron]]
{{div col end}}

==References==
{{Reflist}}

==External links==
{{commons }}
{{Scholia|topic}}
* [https://www.wecanfigurethisout.org/VL/Nanocarbon.htm Nanocarbon: From Graphene to Buckyballs] Interactive 3D models of cyclohexane, benzene, graphene, graphite, chiral & non-chiral nanotubes, and C60 Buckyballs – WeCanFigureThisOut.org. 
*[http://www.chemistry.wustl.edu/~edudev/Fullerene/solidstate.html Introduction to fullerites]
*[http://www.vega.org.uk/video/programme/231 Giant Fullerenes, a short video looking at Giant Fullerenes]

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{{Allotropes of carbon}}
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[[Category:Fullerenes| ]]
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