Synthesis and Structural Examination of Complexes of Am(IV) and Other Tetravalent Actinides with Lacunary Heteropolyanion α₂-P₂W₁₇O₆₁¹⁰⁻

Abstract

This study concerns the formation of complexes with actinides at oxidation state +IV, from Th to Am, through a lacunary heteropolyanion ligand P(2)W(17)O(61)(10-). The preparation of original single crystals of complexes with 1:2 stoichiometry provided structural data through single-crystal X-ray diffraction for the entire An(IV) series. An(IV) atoms in these complexes have a coordination number of 8, and their coordination polyhedron is a distorted square antiprism. The data were used to compute a mean (An-O) interatomic distance for each actinide. When the interatomic distance is plotted versus the inverse ionic radius of these tetravalent actinides, it appears that the simple electrostatic model is not suitable for Am(IV) and Pu(IV), although this trend must be confirmed by further investigation with other examples from the An(IV) series.

Influence of the pH on the Condensation of Tetravalent Cerium Cations in Association with [α‐SiW9O34]10– Leading to the Formation of a Ce6O4(OH)4 Core

“…To the best of our knowledge, related molecular materials are relatively rare in the literature as only few examples of POMs coordinated to tetravalent 4f, 5d, or 5f elements can be found. These species are generally obtained by complexation of the tetravalent cations (sometimes mixed with 3d metals) by vacant Keggin‐ or Dawson‐type polyoxotungstates, giving rise to 1:2 sandwich‐type compounds such as [M IV (XW 11 O 39 ) 2 ] 12– or [M IV (XW 17 O 61 ) 2 ] 16– (with M = U, Th, Np, Pu, Cm and X = As, P, Si, Ge) or more complex systems with polyvacant units . Some rare examples of POMs stabilizing trimeric or hexameric condensed zirconium or hafnium cations were also synthesized by other research groups , .…”

A small-angle X-ray scattering study of aqueous solutions of uranium(IV) complexes with lacunar heteropolytungstates

“…The crystal structure of some of these compounds was studied previously by single crystal X-ray diffraction [7]. A sample for small-angle studies was prepared as follows.…”

“…It should be noted that the complexes in solutions can exhibit ordering 4. Examples of reconstruction of the aggregate shapes from small-angle scattering data (views along different directions) and aggregate shape according to single crystal X-ray diffraction (adapted from [7]). …”

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

“…[48][49][50][51] From 2003, the related molecular moieties were structurally characterized and similar 1:2 sandwich molecular systems of formula [An IV (PW 17 O 61 ) 2 ] 26were revealed with the series of tetravalent cations An IV = Th IV , U IV , Np IV , Pu IV and Am IV . 52,53 In the case of uranium(IV) and thorium(IV), it was noticed that the compounds could exist as "syn" and "anti" configurations in the presence of pure  1 or  2 POM isomers or with a  1 - 2 POM mixture ( Figure 6). 31 P NMR spectroscopy on the uranium-based POM moiety shows that at least two species are present in aqueous solution and interconvert slowly on NMR time scale.…”