Hexagons and pentagons

Bnckminsterfullerene (buckyball). (a) The arrangement of the 60 carbon atoms in a buckyball. (b) The identical arrangement of the hexagons and pentagons on the surface of a soccer ball. 

Until 1985, the only known elemental forms of carbon were diamond, graphite, and amorphous carbon. Then Kroto et al. announced the discovery of C6o, a spherical arrangement of carbon atoms in hexagons and pentagons, as shown in Figure 17.7. They called this form Buckminsterfullerene after the architect Buckminster Fuller, who developed the geodesic dome. The name for this type of carbon molecule has since been shortened to fullerene, but it is commonly called a buckyball. Since this first discovery, it has been found that fullerenes can be made in quantity from electrical arcs between graphite electrodes. About 75% of... 

Figure 10.47. Structure (j) (truncated icosahedron) is well known to the chemical community as buck-minsterfullerene, C6o, comprising hexagons and pentagons. It has been well established, both chemically and geometrically, that the pentagons in the structure are necessary to effect three-dimensional closure, and without them only open, two-dimensional graphitic layers are formed. All fullerenes, and even the topical Bucky tubes (Figure 10.2), that consist of fused hexagons are open at both ends unless pentagons are incorporated into the structure.

Recent synthetic studies have shown that carborane skeletons larger than the icosahedron can be constructed by the insertion of additional BH units. The reaction scheme and structure motifs of these carborane species are shown in Fig. 13.4.15. Treatment of 1,2-(CH2)3-1,2-C2BioHio (1) with excess lithium metal in THF at room temperature gave [(CH2)3-l,2-C2BioHio][Li4(THF)s] 2 (2) in 85% yield. X-ray analysis showed that, in the crystalline state, both the hexagonal and pentagonal faces of the carbon-atoms-adjacent arachno-carborane tetra-anion in 2 are capped by lithium ions, which may in principle be substituted by BH groups. 

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