What is fullerene

Fullerenes

History, manufacture

Long before the production of the first fullerene in 1985, Harry P. Schultz published a scientific article in 1965 in which he established the existence of a spherical C.60H60Molecule thought possible [5].

Five years later, in 1970, the Japanese chemist Eiji Osawa predicted on the basis of calculations that large spherical molecules made up of carbon atoms could exist that do not contain hydrogen atoms[2]. Unfortunately, the article in question only appeared in Japanese, so that Western scholars only read it a few years later.

1985 fullerenes were then by Robert F. Curl jr. (USA), Sir Harold W. Kroto (England) and Richard E. Smalley (USA) man-made [6]by evaporating graphite with the help of laser beams[1,2]. In 1996 they received the Nobel Prize in Chemistry for this, while Osawa was not taken into account [6]. During this manufacturing process, hollow spheres made of 60, 70 and more carbon atoms were created, reminiscent of soccer balls.

Further details on the production process can be found in Wikipedia, article "Fullerenes - Production".

structure

The best known and best researched fullerene is Buckminster fullerene made of 60 carbon atoms, also known as "buckyball" in English.

The Buckminster-Fullerene was named after the English architect Buckminster-Fuller, who constructed a large dome made of hexagonal and pentagonal cells for the Montreal Expo in 1967.

The C60-Molecule, just like a soccer ball, consists of 20 hexagons and 12 pentagons; it has a diameter of 700 pm. The carbon atoms in the fullerenes are like in graphite and in graphene sp2-hybridized. The pz-Orbitals protrude inwards and outwards from the sphere, so that the sphere has a high electron density both on the inside and on the outside.

While the pi-electrons are delocalized in graphite and bind a cloud of electrons, they are not delocalized in the fullerenes, but concentrate in the hexagons [1].

The Size comparison is interesting - also for chemistry classes: If you were to do the C60-Molecule to the size of a soccer ball, then one would have to enlarge a soccer ball to the size of the globe [2].

properties

Physical Properties

Fullerenes are usually brown to black powders with a slight metallic sheen. In the air they quickly disintegrate into graphite. But they can also occur as a mineral fullerite (C.60). This mineral then has a density of 1.9 to 2.0 g / cm3 and a hardness of 3.5, so it is significantly harder than graphite [3].

While graphite and diamond are hardly soluble in any solvent, fullerenes can be dissolved in organic solvents, often with a distinctive color. The C60-Fullerene, for example, dissolves in toluene with a wine-red color [2].

Fullerenes can be sublimated at approx. 400 ºC [6].

Chemical properties

Chemically, fullerenes are characterized by the high reactivity of the C – C bonds towards the outside, which is due to the pz-Orbitals of the sp2-hybridized carbon atoms [4]. Therefore, fullerenes can easily bind atoms or molecules on the outside. Basically, these are electrophilic addition reactions.

For this reason, the possibility of using fullerenes as radical scavengers, which should slow down the aging processes in human cells, is also being discussed. However, there is still no scientific evidence for this [6].

Covalent bonds in the interior of a fullerene have not yet been demonstrated, but there are so-called inclusion compounds [4], that is, atoms or molecules can be enclosed in a fullerene like a cage. This possibility then leads to interesting applications in which one uses fullerenes as a means of transport for other compounds.

A third way to carry out chemical reactions with fullerenes is to substitute other atoms for carbon atoms. For example, you could use the connection C59Produce N in which a C atom has been replaced by an N atom [6].

Occurrence

At first, fullerenes could only be produced artificially, and the procedures for doing this were sometimes quite complex. The synthesis of C60 took place, for example, in 12 individual steps [1]. In the meantime, however, natural occurrences of fullerenes have also been discovered.

In 2010, fullerenes were also discovered in space, and there is now even a theory that all carbon came from space to earth through fullerenes [4].

use

So far, no significant applications for fullerenes have really been found.

Theoretically, they could be used in medicine as a carrier to transport certain drugs in the body, because easily degradable compounds can be locked in fullerene cages and thus protect against the body's enzymes and immune system. However, the costs for such procedures would be very high [4]. Cage molecules are also being used in cancer research. Fullerenes can be chemically modified to be taken up by cancer cells. There they could deliver certain drugs or trigger chemical reactions that destroy the cells [7].

Fullerenes have already been used for organic solar cells, but not yet on a large scale [6].

Swell:

  1. Riedel, Jannik, Inorganic Chemistry, Berlin 2007, p. 512ff.
  2. Fullerenes - Materialinfo, at www.nanopartikel.info, accessed on May 19, 2020.
  3. Fullerene, at www.mineralienatlas.de
  4. Fullerene, in the lexicon of biology published by Spektrum-Verlag.
  5. Topological Organic Chemistry. Polyhedranes and Prismanes. Published by Harry P. Schultz in 1965 in J. Org. Chem.
  6. Fullerenes, German Wikipedia, accessed on May 19, 2020
  7. Fullerene - Tumor reserch, English Wikipedia, accessed on May 19, 2020