Scientists announce a breakthrough in transuranium-actinide chemical bonding

Researchers from The University of Manchester were able to create a transuranium compound where the central metal, here called neptunium forms multiple bonds to one element. This breakthrough is crucial for the clean-up of nuclear waste.

Report in the journal Nature Chemistry that a team of researchers from The University Manchester and the European Commission Joint Research Centre Karlsruhe successfully created and characterized the long-awaited transuranium chemical bonds scenario in an isolable substance.

With decades of extensive research, the study of multiple metal-element bond interactions is a huge area of chemistry research. It has been a long-standing field of chemistry research that has sought to understand chemical bonds, reactivity, and separations applications. There is a lot of interest in understanding covalency in chemical bonding in extraction studies. This could help in the separation and cleanup of nuclear waste.

However, while multiple metal-element bond investigations are well documented across the Periodic Table up to uranium (the heaviest element to naturally occur in significant amounts), investigations involving transuranium components, which are elements that come to the following uranium on the Periodic Table, such as neptunium have been limited due to the necessity to perform work on radioactive elements in specialist facilities.

Due to the limited experimental work in transuranium-element multiple bonds, there is little knowledge transfer from these fundamental studies into potential separations applications.

Examples of transuranium-element multiple bonds chemistry have been found. These include two or more elements multiple bonds to a transuranium Ion to allow for sufficient stabilization to allow isolation of the compounds. These linkages cannot be examined in isolation due to the presence of multiple bonded elements. This complicates their analysis. It has not been possible to access transuranium compounds with only one multiple bond to an element stable enough to isolate. This makes it difficult to experimentally verify or disprove theoretical predictions.

The researchers were able to prepare a complex that contained a neptunium-oxygen ion and multiple bonds to one oxygen atom using specialist handling equipment. It was important to carefully design the supporting, cage-like organic binding framework that included four stabilizing nitrogen donors as well as a large silicon-based flanking group to help protect the neptunium oxygen bond and allow for its isolation.

The researchers extended their prior work on uranium to neptunium and were able to make previously impossible comparisons. They were surprised to discover that the neptuniumoxygen complex has greater covalent chemical bonding than an isostructural-uraniumoxygen complex. This is the opposite of predictions and highlights the difficulty in making predictions in this area.

The research was coordinated by Professor Steve Liddle (Co-Director of The University of Manchester’s Centre for Radiochemistry). He stated that the work was possible because of the collaboration between international specialists and the talents of the researchers involved in the study.

This was difficult work experimentally. It would not have been possible without three leading institutions combining their strengths to embrace our interdisciplinarity research approach. But it has been crucial because this work already highlights how predictions can easily be broken down in this complex area. This shows how important it is to experiment and test theories in order to establish benchmarks for the future.

Through the study of metal-element multiple bonds, thorium and molecular uranium chemistry have made great strides in recent years. However, transuranium science is still far behind because of the difficulties of working with these elements experimentally. This research shows that transuranium analogs can now be studied more widely, which opens up new opportunities for actinide science.