Carbon cages with heteroatoms

There is mass spectroscopic evidence for clusters C59B, C68B2,. ..C54 B6 in the products of laser ablation of boron nitride/graphite composites (Guo et al. 1991). It is proposed that these may be versions of the fullerene cage in which heteroatoms have occupied carbon sites with little disturbance of the framework. This is a plausible hypothesis for low doping ratios, in view of the ability of carbon to substitute for boron in carboranes. Bond-energy considerations suggest that... 

Ordinarily, a fullerene composed of n carbon atoms with a metal atom, M, will simply be represented as MC regardless of whether the metal atom is inside or outside the cage. However, to facilitate discussion of these and more complicated fullerenes with one or more atoms inside, some attached outside and possibly one or more heteroatoms substituting for carbons in the cage network itself, a more explicit symbolism is essential. We will use a set of... 

This review covers the 2000 hterature of carboranes and metallacarboranes and follows essentially the same format as adopted in previous years. Selected heteroboranes of the other members of Group 4 (e.g. Sn) are also included. Carborane complexes are ordered by their formula, with metal complexes included in a separate, appropriately ordered, section. Those complexes with both a carbon and another heteroatom in the cage have been included in the appropriate section on the basis of the carbon atom count. Exo metalla-sub-stituted carboranes are included in the appropriate carborane section. The literature pubhshed has been searched using Web of Science, CAS and the Cambridge Crystallographic Database. Due to space hmitations, descriptions of specific results are kept to a minimum, with the reader directed to the original paper for more information. 

The tendency of atoms of certain elements to form chains with themselves (homoatomic catenation) or in alternation with other atoms (heteroatomic catenation) is of extreme importance in chemistry. The immense subject of organic chemistry and, indeed, life as we know it depend on the special ability of carbon to catenate from the chemical engineering standpoint, catenation and the associated ability to form molecular rings and cages provide opportunities to make materials of desired mechanical, electrical, thermal, chemical, or catalytic properties. 

It has been shown that triphenyl(p-cyanobenzyl)phosphonium tetrafluoroborate (16), which exhibits a a LUMO level localized predominantly on the heteroatom and benzylic carbon, gives products derived from out-of-solvent cage chemical reactions on direct irradiation (reaction 6). This behaviour is connected with the nuclear hyperfine coupling constant of the heteroatom in triphenylphosphine radical-cation171. 

Heterofullerenes are compounds with one or more heteroatom substituting for carbon atoms of the cage. 

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