Inorganic & Coordination Chemistry, Short talk
IC-016

From water-stable uranyl(V) to uranium(IV) polyoxometalates.

R. Faizova1, L. Chatelain1, R. Bernier-Latmani1, A. Chauvin1, F. Fadaei-Tirani1, R. Scopelliti1, M. Mazzanti1*
1Swiss Federal Institute of Technology Lausanne (EPFL)

Traditionally pentavalent uranyl was thought of as a highly unstable species of limited environmental importance because of the tendency of aqueous U(V) to disproportionate under most Eh-pH conditions. However, in the last decade, it has been demonstrated that uranyl(V) is a persistent intermediate in the biological and abiotic transformation of soluble uranyl(VI) compounds into insoluble uranium(IV) species (UO2 or U(IV) discrete clusters).

In particular, U(V) is often found in association with Fe-containing minerals such as goethite and magnetite. Besides the importance of this process for ground-water remediation, the role of U(V) remains unclear as there is no appropriate synthetic model to perform the required studies.

The first example of a stable uranyl(V) complex in organic media was reported more than 10 years ago, inspiring very fast development in the field, but none of the reported compounds have shown stability in aqueous media at environmentally relevant pH.

We will present the synthesis of the first uranyl(V) complex that is stable in both organic and aqueous media. This was achieved by using an aminopicolinate ligand, combining the pentadentate binding mode with the ability to form stable complexes with metal ions in water.[1] Additionally, the effect of Fe2+ on the stability of U(V) toward proton induced disproportionation and redox reactions was investigated. Cation-cation interaction between uranyl(V) oxygen and Fe2+ was shown to play an important role in the stabilization of U(V).[2]  Further, the formation of discrete uranium(IV) clusters of various nuclearities (U6 – U38) and the time dependence of the assembly of uranium oxo clusters in hydrolytic conditions in organic solvent will also be demonstrated.[3] Finally, the first example of direct conversion of a uranyl(VI) complex to a well-defined molecular U(IV) oxo/hydroxo cluster in aqueous conditions will be presented.[4]

[1] Radmila Faizova, Rosario Scopelliti, Anne-Sophie Chauvin, Marinella Mazzanti, Journal of American Chemical Society 2018, 140, 13554-13557.
[2] Radmila Faizova, Sarah White, Rosario Scopelliti, Marinella Mazzanti, Chemical Science 2018, 9, 7520­-7527.
[3] Lucile Chatelain, Radmila Faizova, Farzaneh Fadaei-Tirani, Jacques Pécaut, Marinella Mazzanti, Angewandte Chemie International Edition 2019, 58, 3021-3026.
[4] Radmila Faizova, Farzaneh Fadaei-Tirani, Rizlan Bernier-Latmani, Marinella Mazzanti, Angewandte Chemie International Edition 2020, 59, 6756-6759.