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Nuclear Chemistry Research Advances with Innovative Approaches

Heavy actinides—elements situated at the bottom of the periodic table, beyond plutonium—pose significant challenges for scientific exploration due to their radioactive nature and complex chemistry. Historically, these elements have been studied one compound at a time or through indirect methods using safer and non-radioactive alternatives like lanthanides, leaving gaps in our understanding of their properties.

Researchers at Lawrence Livermore National Laboratory (LLNL) have made notable strides in this field with a novel and efficient “serial approach” aimed at the synthesis and examination of heavy actinide compounds. A recent study published in the Journal of the American Chemical Society reveals that americium and curium exhibit distinct chemical characteristics, countering the long-held belief that certain actinides and lanthanides share similar properties.

The study’s authors, Ian Colliard and Gauthier Deblonde, highlight that their dataset represents one of the largest collections of crystallographic and spectroscopic information on americium and curium compounds ever compiled.

Colliard stated, “Our methodology allows for the synthesis, crystallization, and detailed analysis of americium and curium compounds, which are some of the most difficult elements to investigate. The resources at Livermore have made serial chemistry feasible for these elements, an opportunity that wasn’t previously available.”

In their research, the team synthesized coordination complexes of americium and curium, comparing them to their lanthanide counterparts, neodymium and europium. These complexes involve americium or curium atoms coordinated with polyoxometalates (POMs)—stable clusters formed from metal and oxygen. This enabling technology allows detailed study of the actinide elements.

The initial step in generating a POM complex is crucial for the discovery of new compounds. The researchers evaluated the luminescence properties of 25 curium–POM complexes in aqueous environments, yielding a substantial experimental dataset. They successfully isolated seven curium compounds as single crystals, significantly enhancing the understanding of actinide coordination chemistry.

Traditionally, synthesizing these rare actinide compounds required 500 to 5,000 micrograms of the material for a single compound, but the use of POMs reduced this demand to just 1–10 micrograms per reaction. This methodological advancement not only facilitated the efficient synthesis of americium and curium but also holds promise for future studies involving other heavy elements.

The dataset generated highlights that approximately 45% of the structurally characterized curium compounds to date result from LLNL’s research efforts. Deblonde remarked, “The ability to gather extensive data while minimizing the use of limited research isotopes means we can identify genuine chemical trends across various compounds rather than relying solely on isolated single-compound studies. This also enables us to educate the next generation of scientists on elements previously considered too challenging to study.”

Colliard and Deblonde utilized a variety of analytical techniques to investigate the structural, vibrational, and optical properties of the compounds. Through solid-state spectroscopy, they observed unusual vibrational interactions within the curium complexes, suggesting the presence of novel light-emitting pathways. Understanding these pathways is vital for furthering knowledge in luminescent phenomena and the dynamics of electrons in proximity to heavy elements.

The findings challenge the notion of actinide-lanthanide similarities, showcasing that while these groups share some characteristics, americium and curium possess unique chemical behaviors that cannot be accurately anticipated through the study of lanthanides alone. The distinct properties observed throughout the new series of compounds underscore the complex nature of actinides.

Moving forward, the researchers are keen to expand their “serial approach” to additional rare elements with applications in nuclear science, further dissecting the distinctive attributes of elements positioned at the edge of the periodic table.

More information: Ian Colliard et al, Similar but Different: Structural and Spectroscopic Characterization of Series of Neodymium, Europium, Americium, and Curium Coordination Complexes, Journal of the American Chemical Society (2025). DOI: 10.1021/jacs.5c00861

Source
phys.org