fulleride (rus. фуллерид) — intercalated fullerite; in a wider sense — salts (charge transfer complexes) with fullerenes as anions.

Description

Owing to the relatively large size of fullerene molecules, their solid phases, the fullerites, have relatively large intermolecular interstices. The C60 fullerite has one octahedral and two smaller tetrahedral interstices per each fullerene molecule. They can be filled with small molecules or, even more interestingly, with metal atoms. Since the intermolecular forces in fullerites are quite weak, one can achieve rather high degrees of intercalation accompanied by expansion of the molecular lattice due to action of the interstitial atoms. Reported so far are fullerides with sodium, potassium, cesium, magnesium, calcium, strontium, barium, ytterbium, samarium, europium, etc.

The synthesis of fulleride phases can be carried out by means of direct interaction of fullerites (or fullerene solutions) with alkali metals, often under high pressure, electrochemical doping of fullerites, co-deposition of the metal atoms and fullerene molecules form the vapour phase, etc. Further annealing can yield equilibrium phases.

Because of the high electron affinity of fullerenes, their molecules in fullerides are in the form of negative ions. At low degrees of intercalation, metal atoms are located in individual interstices as atomic cations while at higher degrees of intercalation they may form positively charged clusters. Depending on the stoichiometry, fullerides can form both conductor and dielectric phases, and partial polymerisation of fullerene molecules may occur. In fulleride monolayers, some interesting effects of orientational ordering of fullerene molecule were observed at certain stoichiometries. However, the main interest in fullerides is due to their superconductivity. Initially, superconductivity was found in K3C60 with transition temperature of 19 K. At present, the maximum temperature Ts for fullerides at normal pressure is 33 K for Cs2RbC60, and 40 K for Cs3C60 at 15 kbar pressure.

Another interesting class of fullerides is comprised of fullerene salts with organic electron donors, such as tetrakis(dimethylamino)ethylene (TDAE) or metallocenes. Below ca. 20K, such compounds are soft organic ferromagnets.

Illustrations

Crystalline structure of fullerid
Crystalline structure of fulleride Cs3C60.

Authors

  • Zaitsev Dmitry D.
  • Ioffe Ilya N.

Source

  1. The Encyclopedia of Materials Science and Technology Ed. by K. H. J. Buschow, R.W. Cahn, M. C. Flemings et al. — Elsevier Ltd, 2007. —www1.elsevier.com/emsat/

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