Carbon balls with a metal core

Curl, Kroto and Smalley realised early that it should be possible to enclose metal atoms in the fullerene cages and thereby completely change the properties of the metal. The first successful experiment was done with the rare earth metal lanthanum.

Fullerenes in quantities

Five years after the discovery of the fullerenes, the astrophysicists D. R. Huffmann and W. Krätschmer and their co-workers managed to produce fullerenes in larger quantities.

When two rods of graphite are heated to a high temperature by an electric arc discharge in an atmosphere of helium at a pressure of 13 kPa the graphite rods are slowly consumed and soot is formed. Approximately 10% of the soot is made of C₆₀ and C₇₀. The soot is collected and treated with benzene to dissolve the fullerenes, which can then be separated using chromatographic methods.

Useful fullerenes?

C₆₀ can easily accept electrons and form negative ions. With alkali metals (e.g. potassium), C₆₀ forms a new superconducting crystalline material built from a C₆₀ ion with three charges and three positive potassium ions (K₃C₆₀). The material becomes superconducting at 19 K. Because C₆₀ can accept and then donate electrons reversibly, the fullerenes may well become catalysts in chemical processes and replace expensive and poisonous metals.

By a modification of the method for fullerene production, it is now possible to produce the world's smallest tubes - nanotubes - from pure carbon. The tubes have extremely small diameters, approximately a nanometer. They can be closed at one end or both ends. These new materials might find applications in the electronics industry due to their unique electrical and mechanical properties.

During the six years since the fullerenes became readily available to scientists, more than a thousand new compounds have been synthesised and their chemical, optical, electrical, mechanical or biological properties have been tested. The production of fullerenes is still very expensive, which limits their use.

Today there are more than one hundred fullerene patents, but a large-scale commercial use for these exciting fullerenes is still to be found.

 

C₆₀ in numbers

Molecular weight - 720
Density - 1.72 g/cm³
Molecular diameter - 7 Å

The 60 carbon atoms of C₆₀ only give rise to four absorption lines in the infrared region, which confirms its high symmetry (IR lines at 1429, 1183, 577 and 528 cm^-1). All carbon atoms are equivalent (¹³C NMR-signal at 143 ppm in benzene).