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Thesis (Ph. D.)--University of Missouri-Columbia, 2008. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed June 17, 2009). Vita. Includes bibliographical references.

Thesis (Ph. D.)--Duke University, 2008.

Thesis (Ph. D.)--Delft University, 2004. / Includes bibliographical references.

Thesis (Ph. D.)--Delft University, 2004. / Includes bibliographical references.

The aqueous speciation and hydrolysis of actinides in both the presence and absence of organic ligands has been investigated in the pH range 1 - 13. The speciation and hydrolysis of Th4+, U4+ and UO22+ with H3thme, H3tea, H3bic, H3heidi, H3NTA, H2ADA and H3cit have been investigated using various analytical techniques (1H NMR, 13C NMR, IR, UV-Vis(-nIR) spectroscopy and potentiometric titrations). The PHREEQC interactive software suite was used to predict speciation with the formation constants for various complexes calculated in the Hyperquad software suite. Formation constants of Th4+, U4+ and UO22+ hydroxide species have been calculated showing the formation of polymeric complexes. Experiments showed no complexation of actinides by H3thme and H3tea in aqueous solutions. However, 1:3 (M:L) complexation of Th4+ and U4+ was observed with H3bic along with 1:2 (M:L) complexation of UO22+. A variety of 1:1 and 1:2 (M:L) complexes were observed with H3heidi, H3NTA, H2ADA and H3cit for the actinides. Formation constants for complexes of H3NTA with Th4+ and UO22+, H2ADA with Th4+ and H3cit with UO22+ were calculated in Hyperquad. Studies of Pu3+ with H3heidi showed little complexation but 5Me-HXTAH4 showed 1:3 (M:L) speciation. Complexation of PuO22+ by saldien(Et2N)2H2 and salterpyH2 was shown and a secondary band was observed at ~944 nm after multiple days. The functionalities of organic ligands have been shown to have a profound effect on the (partial) hydrolysis of the actinides.

The nuclear industry faces important technical challenges for HLW storage and designing new nuclear fuels. Such materials have to perform under severe conditions and accommodate defects safely. Few materials are suitable for those purposes but certain types of ceramics are promising candidates; among them oxide compounds such as pyrochlores and zirconolites. The aim of this PhD project was to synthesise novel actinide oxide particles, in which two different approaches were taken: controlled hydrolysis and solid state chemistry. Some minerals were naturally doped with actinides and rare earth elements and inspired synthetic formulations of new targeted waste forms for High Level Waste (HLW) instead of other disposal routes. The choice of synthetic pyrochlore and zirconolites as actinide hosts was inspired by the existence of naturally occurring actinide rich minerals. Substitutions within the cubic Y2Ti2O7 were investigated via the respective Y2Ti2-2xFexNbxO7 and Y2-xCexTixFexO7 solid solutions.Controlled hydrolysis was based on previous work with Lewis acidic transition metal cations. It was shown that it was possible to control the hydrolysis products in the presence of chelating organic ligands by carefully controlling the experimental conditions of the system. The same principles should apply to the chemistry of the actinide ions as they too are Lewis acidic. Such chemistry has implications for understanding the behaviour of actinides in nuclear processes within aqueous and organic systems. This project was a collaboration between Sheffield University (Immobilisation Science Laboratory, ISL) and The University of Manchester (Centre for Radiochemistry Research, CRR) through the DIAMOND (Decommissioning Immobilisation and Management of Nuclear waste for Disposal) University research consortium.

The coordination- and organometallic chemistry of uranium complexes bearing the non-carbocyclic ancillary ligand XA2 (4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) has been developed as a major focus of this thesis. A number of air-sensitive actinide chloro complexes and alkyl derivatives featuring reactive An–C bonds were prepared, and investigated using a variety of structural and spectroscopic analytical techniques, including X-ray diffraction, NMR spectroscopy, elemental analysis, and electrochemical methods. The research described in this thesis serves to expand the currently underdeveloped, fundamental chemistry of actinide complexes supported by non-carbocyclic (i.e. non-cyclopentadienyl) ligands. For example, the use of the prototypical xanthene-based ligand XA2 has led to neutral dialkyl uranium(IV) complexes which a) react with alkyl anions to yield anionic trialkyl ‘ate’ complexes, b) C–H activate neutral pyridines to yield organouranium(IV) species featuring cyclometalated pyridine-based ligands, and c) react with Lewis acids to yield rare examples of cationic monoalkyl uranium(IV) complexes featuring coordinated arene ligands. By altering the nature of the arene solvent/ligand, latent catalytic ethylene polymerization behaviour has also been unlocked in cationic XA2 uranium and thorium complexes, and this development may offer industrial relevance. Additionally, new NON-donor ligand designs featuring bulky terphenyl-based substituents (the "XAT" ligand) as well as 1-adamantyl groups (the "XAd" ligand) have been developed; a family of crystallographically-characterized dipotassium XAT complexes have been prepared which feature unprecedented potassium–alkane interactions, and the XAd ligand has been employed for the development of new organometallic thorium chemistry. The developments described in this thesis contribute to an emerging field and delineate new reactivities and structural motifs, providing important steps forward in organoactinide chemistry. / Thesis / Doctor of Philosophy (PhD)

La contamination des espèces vivantes par les éléments actinides est une source de toxicité radiologique et chimique conduisant à des séquelles graves pour l'organisme contaminé. La plupart des données disponibles sur l'interaction des actinides avec les systèmes biologiques sont basées sur des mesures macroscopiques physiologiques et fournissent très peu d'informations structurales et mécanistiques. Du fait de la complexité des systèmes impliqués dans ces processus, il est difficile de décrire la formation des complexes par des méthodes de biochimie. Notre stratégie a donc été d'approcher cette question par des systèmes biomimétiques très simplifiés que sont les peptides, en étudiant les mécanismes intramoléculaires affectés ou induits par l'interaction cation – ligand. Un pentapeptide carboxylique Ac-DDPDD-NH2 nous a servi de molécule de référence et de point de départ pour évaluer l'influence de la nature du peptide sur la topologie des complexes correspondants. Pour ce faire, différents analogues linéaires (permutations Asp/Ala, peptoïdes) et cycliques ont été synthétisés. De plus, dans le but d'incorporer des fonctions hydroxamates (très affines du Fe(III)) dans le pentapetide de référence, l'étude de la desferrioxamine et de l'acide acetohydroxamique a également été entreprise. Cependant, des difficultés de synthèse ne nous ont pas permis de tester ces dérivés. Trois cations actinides au degré d'oxydation +IV ont été sélectionnés (Th, Np, Pu) et comparés au cation Fe(III) souvent considéré comme analogue biologique du Pu(IV). L'agencement spatial du ligand autour du cation dans les complexes en solution aqueuse tamponnée a été étudié par spectrophotométrie et par Spectroscopie d'Absorption des rayons X. Les données spectroscopiques et l'ajustement des spectres EXAFS nous ont permis de rationaliser la topologie des complexes formés en fonction du peptide considéré : complexes mixtes hydroxy polynucléaires pour les séquences linéaires et cycliques, complexes mononucléaires pour la desferrioxamine. D'autre part, des différences notables sont apparues entre le Fe(III) et les actinides(IV), ce qui traduit une différence de réactivité en solution aqueuse. / The contamination of living organisms by actinide elements is at the origin of both radiological and chemical toxicity that may lead to severe dysfunction. Most of the data available on the actinide interaction with biological systems are macroscopic physiological measurements and are lacking a molecular description of the systems. Because of the intricacy of these systems, classical biochemical methods are difficult to implement. Our strategy consisted in designing simplified biomimetic peptides, and describing the corresponding intramolecular interactions with actinides. A carboxylic pentapeptide of the form DDPDD has been at the starting point of this work in order to further assess the influence of the peptide sequence on the topology of the complexes. To do so, various linear (Asp/Ala permutations, peptoïds) and cyclic analogues have been synthesized. Furthermore, in order to include the hydroxamic function (with a high affinity for Fe(III)) in the peptide, both desferrioxamine and acetohydroxamic acid have been investigated. However because of difficulties in synthesis, we have not been able to test these peptides. Three actinide cations have been considered at oxidation state +IV (Th, Np, Pu) and compared to Fe(III), often considered as a biological surrogate of Pu(IV). The spatial arrangement of the peptide around the cation has been probed by spectrophotometry and X-ray Absorption Spectroscopy. The spectroscopic data and EXAFS data adjustment lead us to rationalize the topology of the complexes as a function of the peptide sequence : mix hydroxy polynuclear species for linear and cyclic peptides, mononuclear for the desferrioxamine complexes. Furthermore, significant differences have appeared between Fe(III) and actinide(IV), related to differences of reactivity in aqueous medium.

Les polymères de coordination (PC) présentent un intérêt tant fondamental qu'appliqué de par leur structure et composition modulables ouvrant de nouvelles perspectives au niveau des propriétés chimiques (catalyse, conversion matériaux mous-durs…) et physiques (magnétisme, optique…). L'objectif principal de ces études consiste à vérifier le transfert de la structure, méso-structure et composition du PC vers la céramique obtenue par traitement thermique. Dans ce contexte, ce manuscrit décrit des études sur la conversion de polymères de coordination obtenus à partir d'un auto-assemblage entre des métaux 4f, 5f et de la 2,5-dihydroxy-1,4-benzoquinone (DHBQ). Dans un premier temps, des méthodes de synthèses, aqueuse et anhydre en atmosphère contrôlée, ont été mises au point. Ainsi, plusieurs types de PC ont été obtenus (4f, 4f-4f, 4f-5f), les composés mixtes formant des solutions solides. Après caractérisation de ces composés, leur comportement sous traitement thermique a été étudié. Les principaux résultats montrent que les précurseurs à base de DHBQ obtenus par voie aqueuse possèdent une méso-structure micrométrique, formée par l'assemblage de sous-unités monocristallines possédant la même structure cristallographique quelle que soit la morphologie observée. L'étude de l'assemblage de cette méso-structure a permis de contrôler la morphologie du grain élémentaire (cylindre, cube, disque…) avec une très bonne distribution en taille. La mise en œuvre de systèmes anhydres en atmosphère contrôlée a permis d'accéder à une plus large gamme de paramètres micro-structuraux (surface spécifique, porosité…). Pour l'ensemble des composés de type PC, la conversion thermique en céramique n'a pratiquement pas altéré la morphologie des matériaux. Les aspects microstructuraux ont pu être contrôlés via la méthode de synthèse. / Coordination polymers (CP) are of great academic and industrial interest due to flexible structure and composition and offer prospects for original chemical (catalysis, soft-hard materials conversion…) and physical properties (magnetism, optics…). The major interest of these studies is to check the transfer of the structure, meso-structure and composition from the CP to the ceramic via a thermal treatment. In this context, this thesis describes studies on conversion of coordination polymers obtained by self-assembly of 4f and 5f metal ions with 2,5-dihydroxy-1,4-benzoquinone (DHBQ). Aqueous and anhydrous synthetic ways were developed, which yielded different kinds of CPs (4f, 4f-4f, 4f-5f) ; solid solutions were obtained with the mixed compounds. The products were characterized and their behaviour under thermal treatment was studied. The main results show that the DHBQ-based precursors obtained by aqueous way have a micrometric meso-structure, formed by the assembly of micro-crystalline subunits which all posses the same crystallographic structure. The study of the assembly of the meso-structure allowed controlling the morphology of the elementary grain (cylinder, cube, disk ...) with very good size distribution. The implementation of anhydrous systems in a controlled atmosphere allowed yielded a wider range of micro-structural parameters (surface area, porosity ...). For all CP-type compounds, the thermal conversion to ceramic has barely altered the morphology of the materials. The microstructural aspects could be controlled via the method of synthesis.