Researchers have shown that boron can form a cage-like molecule similar to a buckyball - soccer-ball-shaped molecules of carbon - that helped usher in the nanotechnology era.
Researchers from Brown University in the US, and Shanxi University and Tsinghua University in China have shown that a cluster of 40 boron atoms forms a hollow molecular cage similar to a carbon buckyball.
It's the first experimental evidence that a boron cage structure - previously only a matter of speculation - does indeed exist.
"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.
"The fact that boron has the capacity to form this kind of structure is very interesting," Wang said.
Wang and his colleagues have described the molecule, which they have dubbed borospherene, in the journal Nature Chemistry.
Carbon buckyballs are made of 60 carbon atoms arranged in pentagons and hexagons to form a sphere - like a soccer ball. Their discovery in 1985 was soon followed by discoveries of other hollow carbon structures including carbon nanotubes.
Another famous carbon nanomaterial - a one-atom-thick sheet called graphene - followed shortly after.
After buckyballs, scientists wondered if other elements might form these odd hollow structures. One candidate was boron, carbon's neighbour on the periodic table.
But because boron has one less electron than carbon, it can't form the same 60-atom structure found in the buckyball. The missing electrons would cause the cluster to collapse on itself. If a boron cage existed, it would have to have a different number of atoms.
Wang's previous work suggested that there was something special about boron clusters with 40 atoms. They seemed to be abnormally stable compared to other boron clusters.
On the computer, Wang's colleagues modelled over 10,000 possible arrangements of 40 boron atoms bonded to each other.
The computer simulations estimate the electron binding energy for each structure - a measure of how tightly a molecule holds its electrons. The spectrum of binding energies serves as a unique fingerprint of each potential structure.
The next step is to test the actual binding energies of boron clusters in the lab to see if they match any of the theoretical structures generated by the computer. To do that, Wang and his colleagues used a technique called photoelectron spectroscopy.
The experiments showed that 40-atom-clusters form two structures with distinct binding spectra. Those spectra turned out to be a dead-on match with the spectra for two structures generated by the computer models.
One was a semi-flat molecule and the other was the buckyball-like spherical cage, researchers said.
