Aromaticity and antiaromaticity are important concepts in organic chemistry. They help to explain why molecules have different properties. In particular, they help define and explain how molecules vary in their stability and their reactivity to other substances. The two concepts are rarely found together. But they are found together in analogues of biphenylene. Previously, researchers have only seen biphenylenes that are organic, meaning they include carbon. Now, researchers have created biphenylenes that are metallic, not organic. They incorporated uranium and thorium, two elements in the radioactive actinide series.
The newly synthesized metallic biphenylenes are an important advance in organic chemistry. They demonstrate that actinides can create stable biphenylene analogues that are both aromatic and antiaromatic. Previous work with other types of metallic elements failed to accomplish this goal. The resulting compounds add to our understanding of the quantum chemistry of actinides. The results may lead to advances in energy storage, fuel production, and industrial chemistry.
Scientists have created what appear to be the first metallabiphenylenes, metallic molecules that have both aromatic and antiaromatic rings. Scientists discovered biphenylene in 1941. Biphenylene is unusual because it has both aromatic and antiaromatic characteristics. These characteristics determine a molecule’s structure, magnetism, reactivity, and other properties. Until now, scientists have only identified biphenylene analogues that are rich in carbon. The new analogues use two actinides, a series of elements that are radioactive and metallic. One of the new biphenylene molecules contains uranium, the other thorium. The role of actinides is important, because similar experiments in the past using transitional metals did not produce stable aromatic/antiaromatic structures.
The research is part of a larger product to use quantum chemical methods to study systems containing actinides. It contributes to a key concept in organic chemistry—Hückel’s rule, which proposed how to identify aromatic molecules. The research also creates new molecules that could be important in a variety of energy production and storage applications, as well as applications in industrial chemistry.
Department of Chemistry, University of Minnesota
This work was supported by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences Heavy Element Chemistry program. The work was also supported by the DOE Office of Science Graduate Student Research program and the DOE Office of Workforce Development for Teachers and Scientists. Support also came from Los Alamos National Laboratory’s Laboratory Directed Research and Development program and the lab’s G. T. Seaborg Institute for Transactinium Science. Support also came from the U.S. National Science Foundation.
Pagano, K. et al, “Actinide 2-metallabiphenylenes that satisfy Hückel’s rule,” Nature, 2020, 578, 563 DOI: 10.1038/s41586-020-2004-7]
ChemistryViews: First metallabiphenylene analogues synthesized