As fullerenes (singular: the fullerene ) are hollow, closed molecules (often with high symmetry , eg. I h symmetry for C 60 ) of carbon atoms , that align in the pentagons and hexagons, respectively. In addition to diamond , graphite , Lonsdaleite , Chaoite , carbon nanotubes and graphene, they represent another modification of the chemical element carbon.
The first publication on fullerenes took place in 1970 by the Japanese chemist Eiji Ōsawa , who theoretically predicted and calculated their existence. He published this and the following of his publications in Japanese, which is why the publication by the researcher Robert F. Curl jr. , Which appeared 15 years later on November 14, 1985 in the journal Nature , was published in Japanese . (USA), Sir Harold W. Kroto (England) and Richard E. Smalley (USA) received worldwide attention. They received the Nobel Prize in Chemistry for this in 1996 , while Osawa was not included.
Before these publications on fullerenes there were some on "hollow molecules", for example an article by David Jones in New Scientist 1966, reprinted in the book "Zittergas und schräges Wasser" (p. 27 f.), With calculations on the stability of hollow molecules, whereby the largest known molecules at that time only had a dodecahedron shape, i.e. only contained 20 atoms.
The best known and most stable representatives of the fullerenes have the empirical formulas C 60 , C 70 , C 76 , C 80 , C 82 , C 84 , C 86 , C 90 and C 94 .By far the best-researched fullerene is C 60 , which was named Buckminster fullerene (in English also buckyball ) in honor of the architect Richard Buckminster Fuller because it resembles the geodesic domes he constructed . It consists of 12 pentagons and 20 hexagons, which together form a truncated icosahedron ( Archimedean solid ). Since a classic football has the same structure, it is also called a football molecule ( footballen ).
C 60 was first "manufactured" in 1984 by EA Rohlfing, DM Cox and A. Kaldor. However, the authors misinterpreted the result of their molecular beam experiments in their publication and failed to recognize the special structure and importance of the carbon cluster with 60 atoms. A year later, the research group Harold W. Kroto, James R. Heath , Sean C. O'Brien, Robert F. Curl and Richard E. Smalley provided the correct interpretation of a comparable experiment in 1985. They first hypothesized the football form of the C 60 clusters detected in this way.
A rotating vacuum graphite slice away a short high-pressure helium pulse blown. At the same time, the graphite surface is hit by a laser pulse in the middle of this helium pulse. In the experiment, the laser light had a wavelength of 532 nm, with which an energy of 30 to 40 mJ was transmitted within an irradiation time of 5 ns. The carbon of the graphite suddenly sublimes atomically and combines in the cooling helium environment to form penta- and hexagonal ring structures which, while being driven out of the irradiation room by the helium pulse, combine in a reaction chamber to form carbon clusters of any size, including fullerenes, and in the Mass spectrometer can be detected. However, the yield of C 60 was so low that it was not possible to investigate further properties. In particular, the hypothetical football structure remained unproven.
The Heidelberg experiments
In 1988, UV and IR spectra of traces of coal dust (soot) measured by Wolfgang Krätschmer and intern Bernd Wagner provided the first indication of the existence of the highly symmetrical C 60 molecule . With an idiosyncratic approach to his experiment, the intern succeeded in producing a coal dust sample in the IR spectrum of which four discrete lines appeared, which Krätschmer initially assessed as "pump oil". Wagner had vaporized graphite in a protective gas atmosphere of 50 Torr argon using a contact arc, and for the first time produced small traces of a molecular material whose weak IR spectra agreed well with earlier theoretical predictions for C 60 .
In February 1989 Konstantinos Fostiropoulos took up Wagner's experiment as part of his doctoral thesis. He first improved its contact arc process and subsequently developed two new processes, one using resistance heating for sensitive electrodes and a robust arc process for efficient production, so that finally preparative production on a gram scale per day and the definitive characterization of the suspected football molecule became possible. He developed a binder-free sintering method and produced graphite electrodes from carbon dust of the 13 C isotope (99%) in order to vaporize them by means of resistance heating below 100 Torr He. With this he achieved an (almost) complete isotopic substitution and generated the exotic 13 C 60 , which provided the necessary evidence that the molecular carrier of the IR absorptions was a pure carbon molecule and not a contamination, e.g. by hydrocarbons. Finally, the electric arc process, as well as the extraction of fullerenes from the soot by means of solvents, was developed for industrial production that is customary today.
It was only this Heidelberg manufacturing process that enabled research on fullerenes on a large scale from 1991 onwards: Two graphite electrodes are vaporized in an electric arc under reduced pressure in a static protective gas atmosphere ( helium or argon ) . The steam condenses on the cooling atmosphere and a rising smoke is formed. The soot produced in this way contains up to 15% fullerenes. The generated fullerenes can then be thermally expelled from the soot or, alternatively, can be extracted with a non-polar solvent ( benzene , toluene , ...). You can also extract the prepared soot sample in a Soxhlet extractor . The fullerene mixture obtained consists of approx. 90% C 60 and approx. 10% C 70 . In contrast, higher fullerenes are only formed in traces. By chromatography , e.g. B. on activated carbon and / or silica gel , the fullerene mixture can be separated.
Production using only rational syntheses is also possible, with flash vacuum pyrolysis taking place in the last step . However, the yield with this process is only around one percent, which is why it is significantly more expensive than manufacturing in an electric arc.
Various possibilities for use as a catalyst, lubricant, for the production of artificial diamonds, in medicine, as semiconductors and superconductors are the subject of research.
Due to the bonding in the molecule, it can absorb and bind an extremely large number of radicals ( radical scavenger ). These are said to be partly responsible for the aging process of the skin. However, this effect of fullerenes has not been scientifically proven.
A study from 2012 reported that oral administration of C 60 dissolved in olive oil to rats showed no toxic effects and significantly extended the life span of the rats. A reproduction of this result is still pending.
For a long time, the IUPAC , which is responsible for binding recommendations on the nomenclature of chemical compounds, refused to recognize the common name fullerene. It wasn't until 2002 that she changed her mind and has been recommending the use of fulleran, fullerene, and fulleroid ever since . That means a lot of relief, because by then the correct , i.e. IUPAC-compliant name, e.g. B. des  fullerene (C 60 ), have been:
Structure and stability
Many fullerenes consist of 12 pentagons surrounded by different numbers of hexagons . Due to the impossibility of completely covering a plane with regular pentagons (and hexagons), the spherical curvature results (see picture on the right). The smallest fullerene is a dodecahedron, C 20 , and consists only of pentagonal carbon rings.
C 60 has a diameter of about 700 pm , i.e. 7 · 10 −10 m. The van der Waals diameter , however, is around 1000 pm, i.e. one nanometer or 1 · 10 −9 m. The mass of the C 60 fullerene is about 720 u , and C 60 has icosahedral symmetry. The fullerenes with more than 60 carbon atoms generally have less symmetry, C 70, for example, is approximately an ellipsoid with D 5h symmetry.
The stability of a fullerene is greatest when
- not adjoin the pentagons, but are only surrounded by hexagons ( Fünfeckregel , Eng .: isolated pentagon rule , IPR),
- the aromatic character is pronounced (see aromaticity , although here the so-called spherical aromaticity must be considered).
Fullerenes are closely related to graphene , a modification of carbon in which the carbon atoms form a monomolecular layer with a hexagonal structure. The following series can be formed: graphs (only hexagon, flat)> fullerenes, general (5 and 6 corner, convex hollow molecule)> C 20 fullerene (only 5 corner, dodecahedron, narrowest curvature, smallest volume) .
Reactions of C 60
Fullerenes offer three starting points for chemical modifications. Exohedral adducts are obtained through addition reactions on the double bonds . The replacement of carbon atoms from the cage shell with e.g. B. Nitrogen atoms to the C 59 N is called substitutional doping. Finally, such cage structures also offer the possibility of introducing atoms or compounds into the cavity. Compounds of this type are called endohedral complexes . To identify endohedral complexes, the notation X @ C n has become established in the literature , in which an atom or cluster X is located inside a fullerene cage of n carbon atoms.
C 60 has a cavity with a diameter of 400 μm, in which metal and non-metal atoms can be embedded. One example is the intercalation compound of helium , which is correctly designated with the notation He @ C 60 . He @ C 60 is formed when graphite is evaporated in a helium atmosphere.
Furthermore, C 60 used for aromatics as well as alkenes typical reactions such as hydrogenation , halogenation , ozonolysis and Birch reduction enter. However, as a rule, there is no complete conversion of all double bonds; Composition C 60 F 60 can only be achieved with fluorine .
Other interesting compounds are the ionic alkali metal fullerides: C 60 can be reduced with sodium and potassium . This creates compounds with the composition MC 60 , M 2 C 60 and M 3 C 60 (M = Na, K). KC 60 crystallizes in the sodium chloride structure . The C 60 3− anion is present in K 3 C 60 and forms a cubic - closest packing of spheres , with the K + cations occupying all tetrahedral and octahedral gaps in the crystal structure . K 3 C 60 is a superconductor .
In Anton Zeilinger's group at the University of Vienna (see web link), the interference of C 60 molecules on the lattice was observed. Thus the matter waves postulated by Louis de Broglie were also shown for relatively macroscopic objects.
Fullerenes occur in nature only in economically unusable amounts (concentrations).
With the help of the Hubble telescope , large amounts of the C60 fullerene were detected in interstellar space.
C 60 is suitable as a component in different concepts of organic solar cells (OPV - organic photovoltaic). Such systems are based on an absorber layer which consists of a donor-acceptor combination. Because of its high electron affinity, the C 60 molecule is unique for its role as an electron acceptor and is therefore used almost exclusively in such components. As electron donor on the other hand are a large number of organic molecules, such. B. the thermally stable Zn phthalocyanine , and many polymers are available.
At the Helmholtz Center Berlin for Materials and Energy , a research group led by Konstantinos Fostiropoulos achieved an organic solar cell made of C 60 and Zn phthalocyanine , prepared from the gas phase, with a record efficiency of η = 2.5%. To date (as of 2015), fullerene-based OPV concepts achieve efficiencies of up to 12%. An industrial production of organic solar cells is sought.
- Joachim Dettmann: Fullerenes - The buckyballs are conquering chemistry. Springer Basel AG, Basel 2014, ISBN 978-3-0348-5706-2 .
- Andreas Hirsch, Michael Brettreich: Fullerenes - Chemistry and Reactions. Wiley-VCH, Weinheim 2005, ISBN 3-527-30820-2 .
- Aurelio Mateo-Alonso, Dirk M. Guldi, Francesco Paolucci, Maurizio Prato: Fullerenes: versatile building blocks for molecular machines. In: Angewandte Chemie. 119, No. 43, 2007, , pp. 8266-8272.
- Karsten Strey: The world of fullerenes. Lehmanns Media, Berlin 2009, ISBN 978-3-86541-321-5 .
- Eiji Osawa (大 澤 映 二): Superaromaticity . In: 「化学」 (Kagaku) . tape 25 , 1970, pp. 854-863 (Japanese).
- Z. Yoshida, E. Osawa: Aromaticity . In: Kagaku Dojin . tape 22 , 1971, p. 174-178 (Japanese).
- István Hargittai: The Road to Stockholm: Nobel Prizes, Science, and Scientists Oxford University Press, 2002, ISBN 0-19-850912-X , p. 87
- DB Boyd, Z. Slanina: Introduction and foreword to the special issue commemorating the thirtieth anniversary of Eiji Osawa's C 60 paper . In: Journal of Molecular Graphics and Modeling . tape 19 , no. 2 , 2001, p. 181-184 , doi : 10.1016 / S1093-3263 (00) 00106-6 .
- H. W. Kroto, J. R. Heath, S. C. O'Brien, R. F. Curl, R. E. Smalley: C 60 : Buckminsterfullerene. In: Nature 318, 1985, pp. 162-163 ( doi : 10.1038 / 318162a0 ; HTML ).
- Press release from the Jet Propulsion Laboratory .
- "Production and characterization of supersonic carbon cluster beams" ( Memento of the original from February 14, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- C60: Buckminster fullerene
- Data from Andreas Bart and Werner Marx
- W. Krätschmer and B. Wagner: Molecular lines in the spectra of carbon dust particles produced in the laboratory . In: Klapdor, HV; Jessberger, EK (Ed.): Max Planck Institute for Nuclear Physics Heidelberg, Annual Report 1988 . 1989, ISSN 0543-1727 , pp. 135-136 .
- "It's junk!" Wolfgang Krätschmer in BBC HORIZON episode "Molecules with sunglasses", 01/20/1992, BBC_LSFA479X
- After only four weeks, Bernd Wagner finished his internship without finding out about the explosiveness of his "individual will". He was not taken into account as an author in later publications or in the patenting of the Heidelberg process in the USA. Three years later, on the occasion of an invitation from Konstantinos Fostiropoulos to the MPIK, he was informed about the consequences of his internship at the time.
- For the production and structure verification of fullerenes see dissertation: "C60 - a new form of carbon", submitted by Konstantinos Fostiropoulos at the University of Heidelberg on February 12, 1992, doctoral supervisor and first reviewer Prof. Hugo Fechtig, MPI Nuclear Physics Heidelberg, second reviewer Prof. Walter Roedel, Institute for Environmental Physics, Heidelberg University
- Loose, brittle carbon electrodes with high specific resistance can be evaporated by resistance heating in a vacuum if carefully clamped between Ta electrodes.
- In a non-contact arc, the carbon evaporation rate between two electrodes is much higher than in a contact arc
- first reported in "Dusty Objects in the Universe" conference report, pages 89-93 "Search for the UV and IR spectra of C60 in laboratory-produced carbon dust"
- The infrared and ultraviolet absorption spectra of laboratory-produced carbon dust: evidence for the presence of the C60 molecule
- W. Krätschmer, Lowell D. Lamb, K. Fostiropoulos, Donald R. Huffman: Solid C60: a new form of carbon . In: Nature . tape 347 , no. 6291 , September 27, 1990, p. 354-358 , doi : 10.1038 / 347354a0 .
- Konstantinos Fostiropoulos: C60 - a new form of carbon , dissertation, submitted in February 1992, University of Heidelberg - for quantitative production by means of electric arc and isolation of the fullerenes from the soot.
- W. Krätschmer, Lowell D. Lamb, K. Fostiropoulos & Donald R. Huffman: Solid C 60 : a new form of carbon , Nature 347, pp. 354-358, September 27, 1990, doi: 10.1038 / 347354a0 . - To isolate the fullerenes from the soot.
- Wolfgang Krätschmer: The story of making fullerenes . In: Nanoscale . tape 3 , 2011, p. 2485-2489 , doi : 10.1039 / C0NR00925C .
- Anke Krüger: New carbon materials. Vieweg + Teubner, 2007, ISBN 978-3-519-00510-0 .
- Tarek Baati, Fanchon Bourasset, Najla Gharbi, Leila Njim, Manef Abderrabba, Abdelhamid Kerkeni, Henri Szwarc, Fathi Moussa: The prolongation of the lifespan of rats by repeated oral administration of  fullerene , Biomaterials , Volume 33, Issue 19, June 2012, pp. 4936–4946 ( doi : 10.1016 / j.biomaterials.2012.03.036 )
- carbon nanospheres almost double rat lifespan: a critique - Articles - Articles - Longe City - Longe City . In: LONGECITY . ( longecity.org [accessed October 31, 2018]).
- Andreas Hirsch, Zhongfang Chen, Haijun Jiao: Spherical aromaticity in I h -symmetrical fullerenes: the 2 (N + 1) 2 rule . In: Angew. Chem. Band 112 , 2000, pp. 4079-4081 , doi : 10.1002 / 1521-3757 (20001103) 112: 21 <4079 :: AID-ANGE4079> 3.0.CO; 2-H .
- Markus Arndt, Olaf Nairz, Julian Voss-Andreae, Claudia Keller, Gerbrand van der Zouw, Anton Zeilinger: Wave-particle duality of C 60 molecules . In: Nature . tape 401 , no. 6754 , 1999, pp. 680-682 , doi : 10.1038 / 44348 ( PDF ).
- Mineral Atlas: Shungite .
- MA Cordiner, H. Linnartz, NLJ Cox, J. Cami, F. Najarro, CR Proffitt, R. Lallement, P. Ehrenfreund, BH Foing, TR Gull, PJ Sarre, SB Charnley: Confirming Interstellar C60 + Using the Hubble Space Telescope. In: The Astrophysical Journal. 875, 2019, p. L28, doi: 10.3847 / 2041-8213 / ab14e5 .
- Research group organic solar cells at the Helmholtz-Zentrum Berlin ( Memento of the original from February 12, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- "Preparation and investigation of phthalocyanine / C60 solar cells" , Fostiropoulos et al., 2002 SPIE conference
- Organic solar cells
- http://www.pv-tech.org/news/verified_heliatek_organic_solar_cell_achieves_record_12_conversion_efficien World OPV record
- Dresdner Latest News : Dresden company Heliatek is planning large-scale production of organic solar cells from 2015. , January 28, 2014