The structure of the elusive boron monoxide was finally determined after 83 years

(Nanowerk News) In an effort to find new 2D materials, a team of scientists from Ames National Laboratory determined the structure of boron monoxide. This compound was first discovered in the 1940s and has maintained research interest throughout the years. However, scientists were unable to determine the material’s structure due to technological limitations at the time. Using new NMR methods and analytical tools not previously available, the team from Ames Lab finally solved this deceptively simple structure of matter.

They published their findings in Journal of the American Chemical Society (“Boron Monoxide Structure”). BO structures are an old problem, dating back to 1940. Solving them required the development of new NMR methods as well as applying x-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), x-ray electron spectroscopy (XPS), and transmission electron microscopy (TEM). This research is described here as an archaeological dig. (Image: Ames National Laboratory)

“We didn’t really study this particular material at first,” said Frédéric Perras, a scientist from Ames Lab and member of the research team. “We’re actually trying to create a carbon-free covalent organic framework.” The covalent organic framework is a low-density, porous material with a regularly ordered crystal structure. It consists of organic molecules linked together via covalent bonds.

“However, after many synthesis experiments, we could not get a highly crystalline covalent organic framework material,” said Wenyu Huang, another scientist from Ames Lab and a member of the team. Perras and Huang’s group are interested in this material for alternative energy applications.

The team ended up creating a boron-based material that Perras said was difficult to characterize. Through their research, they found literature dating back to the 1940s that contained descriptions of the exact reaction the team was working on, and the synthesis of a substance called boron monoxide. Unfortunately, scientists were previously unable to determine the material’s structure.

Fortunately, materials research technology has advanced since the 1940s. “Because of our expertise in nuclear magnetic resonance spectroscopy, and the development of new methods that were inaccessible to people in their 40s, 50s, and 60s, we thought that we might be able to put this nearly century-old mystery to rest. ,” Perra said.

Perras explains that boron monoxide is made using precursor molecules that act like building blocks. These molecules stick together through dehydration reactions. The key to shrinking a structure is figuring out how the blocks are physically arranged. “So we developed several NMR methods that allow us to study the orientation of these building blocks relative to one another. Basically, we found that adjacent precursor molecules are arranged parallel to each other, which fits one of the previously proposed models,” said Perras.

“We also applied many other techniques, including powder X-ray diffraction, which showed that these nanosheets self-assemble into what is called a turbostratic array,” said Perras. He explained that these stacked nanosheets are like piles of paper thrown onto a table. Once they land, they don’t align perfectly, but they stay in the stack.

According to Perras, there has recently been a lot of interest in synthesizing new boron-based 2D materials. Understanding the structure of this one could lead to the synthesis of other useful boron-based 2D materials. “What really excites me is just the fact that this is an old issue. These are basic ingredients; when you write down the chemical formula, it is BO. So it’s exciting from that point of view that we’re finally finalizing the structure,” said Perras.