Nanotechnology would not be where it is today without the 1985 discovery of buckminsterfullerene, also known as the “buckyball,” which is a stable arrangement of 60 carbon atoms. In recent years, chemists began to theorize that boron could be similarly arranged; a feat that was accomplished by an international team led Lai-Sheng Wang of Brown University. It is composed of 40 boron atoms, which Wang’s team named borospherene, and looks similar to a buckyball. The molecule was described in detail in the journal Nature Chemistry.
While the buckyball is composed of pentagons and hexagons patterned just like a soccer ball, borospherene’s cage-like structure is made up of heptagons, hexagons, and many smaller triangles. It’s structure is different than what has been predicted, as previous papers believed it would require 38 or 80 boron atoms to make a stable structure; not 40.
"This is the first time that a boron cage has been observed experimentally," Wang said in a press release. "As a chemist, finding new molecules and structures is always exciting. The fact that boron has the capacity to form this kind of structure is very interesting.”
The discovery was made accidentally, as Wang’s lab had been trying to develop a boron version of graphene (a carbon monolayer arranged in a honeycomb pattern). They noticed that forty boron atoms became incredibly stable together, but needed to verify the shape. Over 10,000 computer simulations were created in order to find out how those 40 atoms could have come together, along with the electron bonding energy.
That bonding energy was then used to compare against the boron that had been created in the lab. Boron was transformed into a vapor by a laser, and the vapor was then frozen using helium, causing the vapor atoms to clump together. The clumps with 40 atoms were isolated and then subjected to another laser that disrupts the structure and helps to find the spectrum of the electron binding energy.
Combining the results of this method, known as photoelectron spectroscopy, and the computer simulations, Wang’s lab discovered that 40 boron atoms took on two shapes: one is borospherene and the other is a mostly-flat molecule.
"The experimental sighting of a binding spectrum that matched our models was of paramount importance," Wang explained. "The experiment gives us these very specific signatures, and those signatures fit our models."
Borospherene may bear a resemblance to buckyballs, but unlike the carbon-based molecule, the bonds within boron structure don’t allow it to function well on its own. The researchers are exploring its utility to be connected into a chain. The bonds are expected to work well with hydrogen and could possibly be useful for storing hydrogen.