Boron monoxide, a binary compound of boron and oxygen, was first reported in the 1940s. However, scientists were unable to determine the structure of the material due to technological limitations of the time. Using new NMR methods and previously unavailable analytical tools, a team of chemists at Ames National Laboratory finally solved the structure of this compound.
The structure of boron monoxide was a longstanding problem, dating back to 1940. Solving it required developing new NMR methods as well as applying x-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), x-ray photo electron spectroscopy (XPS), and transmission electron microscopy (TEM). Image credit: U.S. Department of Energy Ames National Laboratory.
“We initially weren’t really looking into studying this particular material,” explained Dr. Frédéric Perras, lead author of a paper published in the Journal of the American Chemical Society.
“We were actually trying to make a carbon-free covalent organic framework.”
“A covalent organic framework is a low-density and porous material with a periodically ordered crystal structure. It is composed of organic molecules that are linked together through covalent bonds.”
“However, after many synthesis trials, we could not get a highly crystalline covalent organic framework material,” added Dr. Wenyu Huang, senior author of the paper.
The researchers ended up making a boron-based material that they said was difficult to characterize.
Through their research, they came upon literature dating back to 1940 that contained descriptions of the exact reaction the team was working on, and the synthesis of a material called boron monoxide.
Unfortunately, previous scientists were unable to determine the structure of the material.
Luckily, technology for materials research has advanced since the 1940s.
“Because of our expertise in nuclear magnetic resonance spectroscopy, and the development of new methods to which people in the 40s, 50s, and 60s didn’t have access, we thought that we might be able to lay this nearly century old mystery to rest,” Dr. Perras said.
“Boron monoxide is made using a precursor molecule that acts like building blocks. These molecules stick together through dehydration reactions. The key to understating the structure is to figure out how the blocks are physically arranged.”
“So we developed some NMR methods that allow us to study the orientation of these building blocks relative to each other.”
“Basically, we found that adjacent precursor molecules were getting organized parallel to each other, which matched one of the previously proposed models.”
“We also applied a lot of other techniques, including powder X-ray diffraction, which showed that these nanosheets organized themselves into what’s called a turbostratic arrangement.”
These stacked nanosheets are like a stack of paper thrown onto a desk. Once they land, they are not perfectly aligned, but they remain in a stack.
“There has been a lot of recent interest in synthesizing new boron-based 2D materials,” Dr. Perras said.
“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 problem. It’s such a basic material; when you write down the chemical formula, it’s boron monoxide.”
“So, it’s interesting from that point of view that we finally solved its structure.”
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Frédéric A. Perras et al. 2023. The Structure of Boron Monoxide. J. Am. Chem. Soc 145 (27) 14660-14669; doi: 10.1021/jacs.3c02070
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