Understanding half-buckyballs has potential for new materials
Researchers are well on their way to finding a rational synthesis of buckminsterfullerene (C60, or buckyballs) that could help realise the potential of these structures as new materials.
Buckyballs can be harder than diamond, more slippery than Teflon, or turned into insulators or conductors. They will also stabilise reactive molecules inside their hollow interiors. But they can be difficult to manipulate in solution.
Buckyballs will dissolve readily in alkali metal-liquid ammonia to form C605- anions - when sodium dissolves in liquid ammonia it produces a solution of highly reactive, solvated electrons that readily reduce C60 to its anion.
Neal Skipper, reader in material physics at University College London, UK, and his group at the London Centre for Nanotechnology studied anion solvation behaviour in these concentrated solutions.1 Meanwhile, Marina Petrukhina, assistant professor of materials chemistry, and her team at New York’s Albany State University, US, have gathered x-ray crystal data on a half buckyball - C30H12 - called hemibuckminsterfullerene, and its tetra-rhodium(ii) metal complex.2
’Both our works illustrate interactions of the curved unsaturated aromatic carbon surface in these fascinating molecules,’ says Petrukhina.
Using wide-angle neutron scattering and isotopic labelling, Skipper’s team discovered how liquid ammonia solvates fullerenes. Two giant concentric solvation shells of 45 and 80 ammonia molecules each surround a C605- anion with a complex pattern of H-bonding. These shells effectively double the anion’s radius, permitting high fulleride concentrations in solution.
’Knowing how these large anions solvate will enable separation and purification of different fullerenes, and some fascinating new chemistry to be done,’ says Chris Howard, a post-grad in Skipper’s group.
The x-ray data indicate that the half-buckyball molecule is bowl-shaped, chiral and comes in two different polymorphic crystalline forms, stabilised by strong pi-pi interactions. In one form, the half-buckyballs stack like molecular bowls on top of each other.
’Our work should open practical new ways of preparing fullerenes, especially with encapsulated metals in their interiors,’ concludes Petrukhina.
1 C A Howard et al, J. Am. Chem. Soc., 2004, 126, 13228
2 M A Petrukhina et al, Angew. Chem. Int. Ed., 2004, 43, 5645