title: Coordination of Tetravalent Actinides (An=ThIV, UIV, NpIV, PuIV) with DOTA: From Dimers to Hexamers.
abstract: Three tetravalent actinide (AnIV) hexanuclear clusters with the octahedral core [An6(OH)4O4]12+(AnIV=UIV, NpIV, PuIV) were structurally characterized in the solid state and in aqueous solution by using single-crystal X-ray diffraction, X-ray absorption, IR, Raman, and UV/Vis spectroscopy. The observed structure, [An6(OH)4O4(H2O)8(HDOTA)4]⋅HCl/HNO3⋅n H2O (An=U(I), Np(II), Pu(III)), consists of a AnIVhexanuclear pseudo-octahedral cluster stabilized by DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) ligands. The six actinide atoms are connected through alternate μ3-O2-and μ3-OH-groups. Extended X-ray absorption fine structure (EXAFS) investigations combined with UV/Vis spectroscopy provide evidence for the same local structure in moderate acidic and neutral aqueous solutions. The synthesis mechanism was partially elucidated and the main physicochemical properties (pH range stability, solubility, and protonation constant) of the cluster were determined. The results underline the importance of: 1) considering such polynuclear species in thermodynamic models, and 2) competing reactions between hydrolysis and complexation. It is interesting to note that the same synthesis route with thorium(IV) led to the formation of a dimer, Th2(H2O)10(H2DOTA)2⋅4 NO3⋅x H2O (IV), which contrasts to the structure of the other AnIVhexamers.
authors.affiliation: CEA, Nuclear Energy Division, Research Department on Processes for Mining and Fuel Recycling, SPDS, LILA, CEA Marcoule, BP17171, 30207, Bagnols sur Cèze, France.
authors.forename: Christelle
authors.initials: C
authors.lastname: Tamain
authors.affiliation: CEA, Nuclear Energy Division, Research Department on Processes for Mining and Fuel Recycling, SPDS, LILA, CEA Marcoule, BP17171, 30207, Bagnols sur Cèze, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Dumas
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstr. 400, 01328, Dresden, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Hennig
authors.affiliation: CEA, Nuclear Energy Division, Research Department on Processes for Mining and Fuel Recycling, SPDS, LILA, CEA Marcoule, BP17171, 30207, Bagnols sur Cèze, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Guilbaud
keywords: EXAFS spectroscopy; Raman spectroscopy; actinides; hexanuclear clusters; structure elucidation