Boron Buckyballs Roll into View
In 1985 a team of researchers reported in Nature that they were ‘disturbed at the number of letters and syllables’ in the ‘rather fanciful’ name that they had chosen to describe their newly discovered structure. Buckminsterfullerenes – now commonly referred to as buckyballs – are stable clusters consisting of 60 carbon atoms bonded to form hollow spheres. With 12 pentagonal and 20 hexagonal faces, buckyballs are distinctly football-shaped nanostructures.
Several years after the discovery of the carbon-based buckyball, boron analogues started to arouse interest among chemists worldwide. Boron is adjacent to carbon in the periodic table, and so it was hypothesised that it may be possible to create similar boron clusters. Theoretical investigation of these possible structures made significant progress, however to date there had been no experimental evidence that these molecules could actually exist. Now for the first time a boron version of the buckyball has been fleetingly detected by photoelectron spectroscopy.
Lai-Sheng Wang at Brown University and his colleagues have created a cage-like molecule consisting of 40 boron atoms. They first vaporised a piece of boron with a laser, then used jets of helium to freeze the vapour into tiny clusters. Clusters containing 40 atoms were then isolated and a second laser used to knock an electron out of the molecule. The speed at which the ejected electron flies down a long tube was then used to measure the electron binding energy spectrum. The team then compared the measured spectra with computer models of 10,000 different possible arrangements of boron atoms. The matching structure revealed they had created a buckyball-like spherical boron cage.
Unlike carbon buckyballs, the ‘borospherene’ faces are made of triangles, hexagons and heptagons, meaning the molecule is not quite spherical. Preliminary calculations suggest that the boron buckyball may be useful in hydrogen storage, the electron deficiency of boron means it would likely bond well with hydrogen. However, Wang has said it is a little too early to know the possible future uses of boron-based nanostructures, but summarised the discovery by saying, ‘As a chemist, finding new molecules and structures is always exciting.’
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