Researchers have shown that a cluster of 40 boron atoms forms a hollow molecular cage similar to a carbon buckyball. (Photo : Brown University)
Researchers from Brown University in the US, and Shanxi University and Tsinghua University in China have successfully shown that a cluster of 40 boron atoms forms a hollow molecular cage similar to a carbon buckyball.
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This is the first experimental evidence that a boron cage structure, which has previously only been speculated, does in fact exist, according to a Brown University press release.
"This is the first time that a boron cage has been observed experimentally," said Lai-Sheng Wang, a professor of chemistry at Brown who led the team that made the discovery, according to "The fact that boron has the capacity to form this kind of structure is very interesting."
Wang and his fellow colleagues described the molecule, which they called borospherene, recently in the journal Nature Chemistry.
Carbon buckyballs are made of 60 carbon atoms, which are arranged in pentagons and hexagons to form a soccer ball-like sphere.
They made their discovery back in 1985, which was followed by discoveries of other carbon structures including carbon nanotubes and nanomaterial, according to the release.
After buckyballs, the researchers wondered if other elements could form these hollow structures. One was boron, or carbon's neighbor on the periodic table. Since boron only has one less electron than carbon, it can't form the same 60-atom structure found in the buckyball.
Missing electrons would cause the cluster to collapse on itself.
Wang and his colleagues showed in a paper published earlier this year that clusters of 36 boron atoms form one-atom-thick disks, which might be stitched together to form an analog to graphene, called borophene.
Wang's work indicated that there was also something special about the clusters with 40 atoms. They seemed to be unusually stable compared to other boron clusters.
Wang's colleagues modeled over 10,000 possible arrangements of 40 boron atoms bonded to each other, according to the release.
The simulations estimated the shapes of the structures and the electron biding energy for each structure.
Then they tested the actual binding energies of boron clusters to see if they match any of the theoretical structures generated by the computer.
In order to do that, the researchers used a technique called photoelectron spectroscopy, which showed that 40-atom-clusters form two structures with distinct binding spectra. Those turned out to be an exact match with the spectra for two structures made by the computer models, according to the release.
One of them was a semi-flat molecule and the other was buckyball-like.
"The experimental sighting of a binding spectrum that matched our models was of paramount importance," Wang said. "The experiment gives us these very specific signatures, and those signatures fit our models."
Borospherene consists of 48 triangles, four seven-sided rings and two six-membered rings. A number of atoms stick out a bit from the others, making the surface of borospherene a little less smooth than a buckyball.
As far as possible uses for borospherene, Wang said that it is too early to tell. For now, he's just enjoying the discovery, according to the release.
"For us, just to be the first to have observed this, that's a pretty big deal," Wang said. "Of course if it turns out to be useful that would be great, but we don't know yet. Hopefully this initial finding will stimulate further interest in boron clusters and new ideas to synthesize them in bulk quantities."