Bonds and electrical structure in plutonium hybrid materials are being investigated.

The design of next-generation nuclear materials can be improved by learning how electrons are arranged in compounds with actinide elements like uranium and plutonium. Because of their radioactivity and complicated chemistry, these elements are difficult to study. Additionally, the electron organization of these elements—part of an actinide series of related elements—does not conform to theoretical predictions.

Five distinct hybrid materials containing a specific compound subunit of chlorine and plutonium have been created by researchers: the anion [PuCl6]2. They examined the anion’s electronic construction and found that while the electrons in the plutonium-chlorine bonds were for the most part not shared (ionic), they likewise highlighted significant commitments from covalent bonds where the electrons are shared. The quantum-mechanical atom model’s 5f shell was correlated with these covalent bonds. This shell is also where theories about how electrons are organized around atomic nuclei don’t match what scientists see.

The study has been published in the Inorganic Chemistry journal.

From an acidic, chloride-rich aqueous medium, researchers created five distinct hybrid materials: (4XPyH)2[PuCl6], where X = H, Cl, Br, and I; and (4IPyH)4[PuCl6]2Cl. The group included specialists from the Pacific Northwest National Laboratory (PNNL), George Washington College, the College of So Paulo, and the State College of New York at Bison The quantum theory of atoms in molecules and natural localized molecular orbital analysis were then utilized by the researchers to investigate the electronic structure of the [PuCl6]2 anion. The underlying bond mechanism and hybrid atomic orbital contributions to the plutonium-ligand bonds were outlined by the researchers. . The research team also looked at two compounds that were related to each other and had been mentioned in previous papers In order to identify patterns in bonding, the researchers conducted the same level of analysis on materials containing the molecular units [PuO2Cl4]2 and [PuCl3(H2O)5]. .

As bond polarity decreased from [PuCl3(H2O)5] to [PuO2Cl4]2 to [PuCl6]2, the findings showed that the Pu-Cl bonds were mostly ionic, but they also had significant covalent contributions. In a similar vein, the f orbital contribution increased while the s and d orbital characteristics of the Pu-based hybrid atomic orbitals in the Pu-Cl bonds decreased. However, there was little variation in the Cl-based hybrid atomic orbitals. This suggests that the covalent nature of the PuCl bond is enhanced by the 5F shell. Through this level of analysis, the significance of the oxidation state, coordination geometry, and metal-ion charge in the analysis of the plutonium-ligand bond was discovered.

This study’s findings assist scientists in comprehending and predicting the chemical and physical behavior of transuranic elements, which are elements in the periodic table above uranium. This is an important step toward improving the design of nuclear materials for the next generation. Additionally, it may assist in more efficient waste management. This research contributes to the overall objective of resolving the f-electron challenge by gaining new knowledge about the role that the 5F shell plays in the bonds between chloride and plutonium. Settling this is the all-encompassing objective of the Division of Energy’s Office of Science’s Weighty Component Science program.

More information: Robert G. Surbella et al, Plutonium Hybrid Materials: A Platform to Explore Assembly and Metal–Ligand Bonding, Inorganic Chemistry (2022). DOI: 10.1021/acs.inorgchem.2c02084

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