Synthesis, characterization and crystallochemistry of polyoxometalates incorporating actinides and lanthanides as actinides surrogates

La recherche de molécules permettant l’extraction et la stabilisation d’actinides est un sujet majeur de la chimie associée au domaine du retraitement des combustibles usés dans l’industrie nucléaire. Parmi les espèces chimiques, les polyoxométallates vacants, par leurs propriétés modulables d’un point de vue structural et fortement nucléophiles se posent comme de bons candidats pour la complexation des cations métalliques. Dans ce contexte, l’association de polyoxotungstates trivacants vis-à-vis d’actinides tétravalents et hexavalents (thorium(IV), uranium(IV et VI)) et de lanthanides considérés comme simulants d’actinides mineurs a été investiguée. Les études ont concerné la réactivité des précurseurs trivacants de type {SiW9O34}, {AsIIIW9O33}, {AsVW9O34} et {PW9O34} avec les éléments 4f (Ce(IV) et 5f (Th(IV), U(VI)), qui ont donné lieu à la complexation de clusters hexanucléaires {Ce6O8} ou de systèmes polyanioniques incorporant jusqu’à 12 centres actinides Th(IV) ou U(VI). Les espèces de type cryptant {As4W40O140} et {P8W48O184} ont permis d’encapsuler respectivement jusqu’à 4 cations uranium(IV) ou 7,2 cations uranyles par molécules. Le troisième cryptant testé {Na2Sb8W36O132(H2O)4} n’a pas permis la complexation d’actinides. Il se réorganise néanmoins, en formant une entité polyanionique contenant les espèces {SbW10O37} et {SbW8O31} lors de la réaction avec les lanthanides trivalents (Gd --> Lu). Au total, 23 composés cristallisés ont été caractérisés par diffraction des rayons X sur monocristal. Les différents assemblages moléculaires ont fait l’objet de caractérisations physico-chimiques (IR, ATG). Leurs stabilités, notamment en solution aqueuse, ont été mises en évidence par la diffusion des rayons X (SAXS).The research of molecules for the extraction and stabilization of actinides is a key topic in the field of chemistry related to the reprocessing of spent fuels in the nuclear industry. Among the chemical species, vacant polyoxometalates, owing to their modular structural properties and high nucleophilia, are good candidates for the complexation of metal cations. In this context, the association of trivacant polyoxotungstates with tetravalent and hexavalent actinides (thorium(IV), uranium(IV and VI)) and lanthanides considered as minor actinide simulants was investigated. The studies concerned the reactivity of trivacant precursors {SiW9O34}, {AsIIIW9O33}, {AsVW9O34} and {PW9O34} with 4f elements (Ce(IV)) and 5f (Th(IV), (U(VI)), which resulted in the complexation of hexanuclear clusters {Ce6O8} or polyanionic systems incorporating up to 12 actinides Th(IV) or U(VI) centers. Cryptand species {As4W40O140} and {P8W48O184} have encapsulated up to 4 uranium(IV) cations or 7.2 uranyl cations per molecule respectively. The third cryptant tested {Na2Sb8W36O132(H2O)4} did not allow actinide complexation. It nevertheless reorganizes, forming a polyanionic entity containing the species {SbW10O37} and {SbW8O31} during the reaction with trivalent lanthanides (Gd --> Lu). A total of 23 crystallized compounds were characterized by single crystal X-ray diffraction. The various molecular assemblies have been subjected to physico-chemical characterizations (IR, TGA). Their stability, particularly in aqueous solution, has been demonstrated by X-ray scattering (SAXS)

Synthèse, caractérisation et cristallochimie de polyoxométallates incorporant des actinides

International audienc

Trends and new directions in the crystal chemistry of actinide oxo-clusters incorporated in polyoxometalates

International audienc

Incorporation et stabilisation de clusters tétravalents polynucléaires par des polyoxométallates trivacants

International audienc

Crystal chemistry and SAXS studies of an octahedral polyoxo-arsenotungstate nanocluster encapsulating four unprecedented thorium arsenate fragments ({Th3As2On} - n=25 or 26).

International audienc

Influence of pH on Ce IV -[As III W 9 O 33 ] 9− association for the formation of hexanuclear cerium( iv ) oxo-hydroxo-clusters stabilized by trivacant polyanions

International audienceFour hetero-polyoxometalate compounds were obtained in aqueous solution, following the synthetic combination of Na 9 [B--As III W 9 O 33 ] with the 4f tetravalent cerium cation, in the presence of formate ligand at different pH values (ranging from 1.5 to 6). Each of these four molecules [{Ce 6 (µ 3-O) 4 (µ 3-OH) 4 (HCOO) 3,5 } 4 (As III W 9 O 33) 4 ] 2-compound 1, [(Ce 6 (µ 3-O) 4 (µ 3-OH) 4)(H 2 O) 4 (As III W 9 O 33)(HCOO) 9 ] 6-compound 2, [(Ce 6 (µ 4-O) 3 (µ 3-O) 5 (µ 2-H 2 O) 3 (HCOO) 3 (As V W 9 O 34) 3 ] 22-compound 3 and [(W 4 O 10){(Ce 6 (µ 3-O) 5 (µ 4-O) 3 (µ 2-H 2 O))(As V W 9 O 34) 3 } 2 ] 44-compound 4 are constructed around one to four hexanuclear cerium clusters of [Ce 6 O 8 ] type. For the compounds 1-3, the arsenato-polytungstate POM units and formate ligands are associated and participate in the stabilization of one cerium(IV)-bearing hexanuclear unit in a cyclic motif (1), a monomeric POM species for 2, and a trimeric POM species for 3. However, in the last molecular system (4), only inorganic entities are bonded to the hexameric cerium(IV) clusters. From the structural point of view, compound 4 appears as the association of two compound 3 entities, in which the formate ligands have been replaced by an inorganic tungsten-based sub-unit, coming from the partial decomposition of the {As III W 9 O 33 } precursor. The behavior and the association modes of the four molecular species are explained on the basis of the pH variation used for their syntheses. All four compounds have been characterized by single-crystal X-ray diffraction, IR spectroscopy, TGA and SEM/EDX microscopy and ICP analyses. Solution behavior was assessed on compound 3 by using Small Angle X-ray Scattering (SAXS) measurements

Complexation of tetravalent uranium cations by the As4W40O140 cryptand

International audienc

Complexation of uranium(IV, VI) cations by polyoxometalate cryptants

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Etude structurale et SAXS d’un nanocluster octaédrique encapsulant quatre fragments ({Th2AsOn} – n = 25 ou 26)

National audienc

Time-controlled synthesis of the 3D coordination polymer U(1,2,3-Hbtc)2 followed by the formation of molecular poly-oxo cluster {U14} containing hemimellitate uranium(iv)

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