Harold Kroto, James Heath, Sean O'Brien, Robert Curl, and Richard Smalley first discovered the C60 molecules in 1985. C60 is a molecule that consists of 60 carbon atoms, arranged as 12 pentagons and 20 hexagons. The shape is the same as that of a soccer ball (Fig. 11.1). Based on a theorem of the mathematician Leonhard Euler, one can show that a spherical surface entirely built up from pentagons and hexagons must have exactly 12 pentagons. Depending on the number of hexagons, molecules of different sizes are obtained, such as C36, C70. However, C60 is the object to which scientists show most interest. It was named fullerene because of its structural similarity to the geodesic domes of the architect R. Buckminster Fuller. Initially, C60 could only be produced in tiny amounts. So there were only a few kinds of experiments that could be performed on the material. Things changed dramatically in 1990, when Wolfgang Krätschmer, Lowell Lamb, Konstantinos Fostiropoulos, and Donald Huffman discovered how to produce pure C60 in much larger quantities. This opened up completely new possibilities for experimental investigations and started a period of very intensive research. Nowadays it is relatively straightforward to mass-produce C60.
The discovery of C60 has stimulated a large activity in chemistry. It opened up the new branch of fullerene-chemistry that studies the new families of molecules based on Fullerenes. By 1997 about 9000 fullerene compounds were known. In 1991 the alkali-intercalated material K3C60 was found to become superconducting at 18 K, the record for organic superconductors (Iwasa 1994). During the next month the critical temperature was increased to Tc = 35 K in RbCs2C60. These phases exhibit a polymer structure, which is air-stable (Winter et al. 1992). In the same year TDAE C60-Fullerene was supposed to be an itinerant ferromagnet (Stephens 1992). However, its optical conductivity does not display a clear metallic component, which indicates that TDAE-C60 is not an itinerant ferromagnet. In 2002, C60-CHBr3 was prepared as a 117-Kelvin superconducting system (Schon et al. 2001). In the last few years there has been a growing interest in the synthesis of fullerene oligomers, and many researchers have attempted to polymerize fullerene C60 by various methods, such as photoirradiation, high-pressure compression at high temperatures.
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