Structure of boron monoxide found by surprise after 83 years of search

Ames National Laboratory

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They weren’t looking for it. They were just trying to discover new 2D materials.

That’s when a team of scientists from Ames National Laboratory determined the structure of boron monoxide by surprise. This compound was first discovered in the 1940s but scientists were unable to determine its structure for 83 years.

This is according to a press release by the organization published on Tuesday.

“We initially weren't really looking into studying this particular material,” said Frédéric Perras, a scientist from Ames Lab and member of the research team.

“We were actually trying to make a carbon-free covalent organic framework.”

“However, after many synthesis trials, 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 groups were looking into these materials for alternative energy applications.

Using new NMR methods and previously unavailable analytical tools, they finally stumbled on the structure of boron monoxide.

Scientists had been trying to solve this mystery 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,” said Perras.

What the researchers found is that boron monoxide is made using precursor molecules that stick together through dehydration reactions and act like building blocks.

“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,” Perras said.

“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,” said Perras.

These stacked nanosheets are like a stack of paper thrown onto a desk: upon their landing, they are not perfectly aligned, but they remain in a stack.

Now, Perras hopes that understanding this new structure 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 BO. So, it's interesting from that point of view that we finally solved its structure,” said Perras in the statement.

The study was published in the Journal of the American Chemical Society.

Abstract:

Boron monoxide (BO), prepared by the thermal condensation of tetrahydroxydiboron, was first reported in 1955; however, its structure could not be determined. With the recent attention on boron-based two-dimensional materials, such as borophene and hexagonal boron nitride, there is renewed interest in BO. A large number of stable BO structures have been computationally identified, but none are supported by experiments. The consensus is that the material likely forms a boroxine-based two-dimensional material. Herein, we apply advanced 11B NMR experiments to determine the relative orientations of B(B)O2 centers in BO. We find that the material is composed of D2h-symmetric O2B–BO2 units that organize to form larger B4O2 rings. Further, powder diffraction experiments additionally reveal that these units organize to form two-dimensional layers with a random stacking pattern. This observation is in agreement with earlier density functional theory (DFT) studies that showed B4O2-based structures to be the most stable.