Speaker: Prof. Thierry LOISEAU

Time: Thursday, 2018.07.26, am 9:00

Location: First floor conference room, 402, Dushu Lake Campus

Abstract

Coordination polymers are built up from the association of metallic centers with organic (e.g. O- or N-donor) ligands. In the particular case of actinides (An), precedent studies have reported mainly the synthesis of such solid networks bearing U(VI) or Th(IV), while trans-uranium elements have been much less studied due to their high radiotoxicity and limited amount of the material source. Among the possible oxidation states of An, the tetravalent state has been investigated most actively and large polyoxo clusters have been isolated for U or Pu. In contrast, there are very few data concerning Np(IV) compounds. The knowledge of the formation of such polynuclear An(IV) species could be of significant importance for the fate of An in contaminated soils containing O-donor ligands, such as humic acids, or other organic pollutants (e.g. phthalates).

In the present communication, we firstly present the formation of several series of uranyl-organic frameworks associated to poly-carboxylate linkers, by following the pH variation parameter of the reaction medium, related to the hydrolysis rate. This strategy was then applied to actinides(IV), which are known to exhibit a strong affinity for hydrolysis reaction in order to form inorganic entities with high nuclearities. In a first approach, the control of water content in reaction media containing organic solvent will be investigated in different chemical systems with Th(IV) and U(IV) in the presence of dicarboxylic acids molecules (typically terephthalic acid), and was then extended to Np(IV) for some cases. The structural descriptions of the different coordination polymers will point out the nuclearityvariation of the inorganic bricks from mononuclear [AnO₉] up to hexanuclear entities [An₆O₈]. The particular case of the poly-oxo cluster [An₃₈] will be discussed, and its formation will be described with U(IV) and Np(IV) in different organic solvents.The last point deals with the isolation and crystallization of polynuclear clusters of actinides (Th(IV)/U(IV)) embedded within large anionic polytungstate moieties ([SiW₉O₃₄], [AsW₉O33]). Polynuclear motifs bearing actinides(IV) have thus been identified in these systems.