Spectroscopy for Plutonium Polynuclear Species in Solution and Application of Model Structures in Data Analysis

Understanding the structure of polynuclear plutonium ions in aqueous solution is crucial to develop separations technologies, predict the long-term behavior of actinide materials in wet systems and model accurately solution to solid precipitation mechanisms. It is an euphemism to say that plutonium chemistry in aqueous solution is complex. Diverse and multifaceted species has been identified and, most often, several of which coexist with each other. In this context, the structural information provided by EXAFS measurements can be a lighthouse for the chemist and the rich visible/near infrared plutonium absorption properties is an excellent asset too. Nevertheless none of which are easy to interpret because few structural models are available for plutonium. This presentation aims to recall how multiple spectroscopic approaches can benefit from reference structures (crystallographic and/or theoretical) to identify plutonium compounds in solution focusing on plutonium hydrolysis compounds and polycondensation in aqueous solutions.<br/> <br/>Single crystal X-ray diffraction and spectroscopies has been applied to describe small plutonium clusters in solution.[1-3] Apart from the structural description, this plutonium hexanuclear core resulted in a peculiar absorption spectrum in the visible range that is a valuable footprint to detect it in several systems. The other actinide cluster geometries known [4-7] are also useful to support spectroscopic analysis in complex plutonium solution including nanomaterials. EXAFS spectra derived from crystal structures and ab-initio calculations how the cluster geometry and nuclearity translates into EXAFS scattering paths and may help to identify the plutonium clusters in solution.[8] This approach is one among others that is used to study larger plutonium assemblies. Overall, several structural and electronic properties of the nanosized plutonium oxides and colloids may be compared and analyzed on the basis of molecular bonds from plutonium clusters.[9-10] And ultimately, in the plutonium ions route to from colloidal suspensions or PuO₂ nanoparticles, polynuclear plutonium clusters are found to be an intermediate species, that the appropriate spectroscopic tools may help to capture. <br/> <br/>[1] C. Tamain, T. Dumas, D. Guillaumont, C. Hennig and P. Guilbaud, European Journal of Inorganic Chemistry, 2016, 2016, 3536-3540.<br/>[2] C. Tamain, T. Dumas, C. Hennig and P. Guilbaud, Chemistry-a European Journal, 2017, 23, 6864-6875.<br/>[3] T. Dumas, M. Virot, D. Menut, C. Tamain, C. Micheau, S. Dourdain and O. Diat, Journal of Synchrotron Radiation, 2022, 29, 30-36.<br/>[4] K. E. Knope, S. Skanthakumar and L. Soderholm, <i>Inorganic Chemistry</i>, 2015, <b>54</b>, 10192-10196.<br/>[5] L. Soderholm, P. M. Almond, S. Skanthakumar, R. E. Wilson and P. C. Burns, <i>Angewandte Chemie-International Edition</i>, 2008, <b>47</b>, 298-302.<br/>[6] G. E. Sigmon and A. E. Hixon, Chemistry-a European Journal, 2019, 25, 2463-2466.<br/>[7] R. E. Wilson, S. Skanthakumar and L. Soderholm, Angewandte Chemie-International Edition, 2011, 50, 11234-11237.<br/>[8] G. Chupin, C. Tamain, T. Dumas, P. L. Solari, P. Moisy and D. Guillaumont, Inorganic Chemistry, 2022, 61, 4806-4817.<br/>[9] C. Micheau, M. Virot, S. Dourdain, T. Dumas, D. Menut, P. L. Solari, L. Venault, O. Diat, P. Moisy and S. I. Nikitenko, Environmental Science-Nano, 2020, 7, 2252-2266.<br/>[10] A. Romanchuk, A. Trigub, T. Plakhova, A. Kuzenkova, R. Svetogorov, K. Kvashnina and S. Kalmykov, Journal of Synchrotron Radiation, 2022, 29.