Researchers dive deep into bismuth complexes

Team of the MPI für Kohlenforschung publishes in “Science”

May 19, 2023

To be able to exploit the advantages of elements and their molecular compounds in a targeted manner, chemists have to develop a fundamental understanding of their properties. In the case of the element bismuth, a team from the Max Planck Institut für Kohlenforschung has now taken an important step.

Chemists at the Max Planck Institut für Kohlenforschung aim at the rational design of chemical processes that lead to more efficient and sustainable chemistry for academia as well as industry. A fundamental understanding of the properties of elements such as bismuth and their molecular compounds is necessary in order to be able to take advantage of their potential for catalysis.  A team led by Josep Cornellà and Frank Neese, group leader and director at the Max Planck Institut für Kohlenforschung, has now found that there are still some "white spots" in the chemical landscape that need to be tapped. The researchers have now published their work on an intriguing property of new bismuth complexes under the title Synthesis and isolation of a triplet bismuthinidene with a quenched magnetic response in the journal "Science"

Special interest in a special element

Why bismuth? Research group leader Josep Cornellà’s team has been interested in this particular metal for quite a while. "Bismuth can offer some advantages - compared to other metals. For example, it is more readily available and less toxic than other elements. In addition, special properties of bismuth that other "classical" catalysis candidates do not have could play a role in future reaction designs," Cornellà explains. 

What is it that makes the Mülheim Bismuth molecule so special? Atoms consist of the atomic nucleus as well as an atomic shell formed by electrons. When molecules are synthesized from atoms or fragments, usually pairs of electrons from different atoms come together to for chemical bonds. However, chemists are often interested in situation that deviate from this situation, which is the case when the molecules have unpaired electrons. Such systems tend to be highly reactive and will readily interact with other molecules.

"Normally, molecules with unpaired electrons are always magnetic," explains Frank Neese. But now the researchers of the Kohlenforschung have developed a molecule containing bismuth that has unpaired electrons and yet, strangely enough, shows no magnetism at all. The solution to this riddle has to do, among other things, with the special position of bismuth in the periodic table of the elements. Bismuth is the heaviest of the stable elements - all subsequent elements are radioactive. Due to the particularly heavy atomic nucleus, the electrons show a special behavior, which can only be understood with the help of Einstein's theory of relativity.

Quantum Chemistry Program from Mülheim

These properties lead to the initially perplexing experimental finding. "Our molecule is not really 'non-magnetic'", the researchers explain, "but there is no magnetic field on Earth strong enough to detect magnetism in our system". The fact that the reseachers were able to calculate the fascinating properties of this molecule from first principles of physics is due to the quantum chemistry program package ORCA, developed in Mülheim and widely used throughout all chemical disciplines by tens of thousands of chemists worldwide.

With their work, the scientists from Mülheim have added an important point to the "chemical profile" of bismuth. This may be of importance in the future when designing new types of catalysts.

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