The many roles of mellitic acid during barium sulfate crystallization

The various roles of mellitic acid during barium sulfate crystallization from nucleation to mesocrystal formation are explored and elucidated

Complexes polynucléaires d'Uranium (structure réactivité et propriétés)

L'étude et la compréhension de la chimie fondamentale des actinides constitue un axe de recherche privilégié notamment dans le cadre de la technologie nucléaire tant en amont pour le développement de nouveaux combustibles qu'en aval pour l'étude du retraitement des déchets nucléaires. Une des problématiques principales au cours de ces études réside dans la capacité que possèdent les actinides à subir des réactions rédox et à former des assemblages polynucléaires. Néanmoins, très peu d'assemblages polynucléaires peuvent être synthétisés de manière reproductible, la plupart des complexes polynucléaires d'actinides décrits dans la littérature sont formés de façon fortuite plutôt que par conception rationnelle. En outre, les assemblages polynucléaires s'uranium ont été identifiés comme particulièrement prometteurs pour l'élaboration de matériaux magnétiques et pour leur réactivité. L'objectif de ce travail réside dans la synthèse d'assemblages polymétalliques à base d'uranium en mettant à profit quelques aspects de sa réactivité redox et de sa chimie de coordination. De nouvelles voies de synthèse de composés polynucléaires d'uranium ont été développées, et l'étude des propriétés physico-chimique des composés a été réalisée. La première approche utilisée repose sur la synthèse d'assemblages d'uranyle pentavalent. L'uranyle pentavalent est connu pour sa facilité d'agrégation via des interactions entre groupement uranyles appelées interaction cation-cation, mais l'isolation de ce type de composé a été très largement limitée par l'instabilité de l'uranyle(V) vis-à-vis de la dismutation. L'utilisation de ligands base de Schiff de type salen a permis dans ces travaux l'isolation du premier assemblage polynucléaire d'uranyle(V). Sur la base de ce résultat, la variation des ligands et des contre-ions utilisés a permis l'isolation d'une large famille d'assemblages polynucléaires d'uranyle(V) et l'étude fine des paramètres régissant leur stabilité. Par ailleurs, l'étude des propriétés magnétiques de ces assemblages a mis en valeur de rares exemples couplages antiferromagnétiques. En outre, cette voie de synthèse a été exploitée pour synthétiser le premier cluster 5f/3d présentant des propriétés de molécule aimant. Le deuxième axe d'approche suivi dans ce travail repose sur l'isolation de clusters oxo/hydroxo d'uranium. La réactivité d'hydrolyse de complexes d'uranium trivalent en présence de ligand à pertinence environnementale à permis la synthèse d'assemblages d'uranium dont la taille à pu être variée en fonction des conditions de synthèse employées. Enfin, de nouveaux assemblages présentant des topologies originales ont été isolés en exploitant la réactivité de dismutation de précurseurs d'uranium pentavalent.The study and comprehension of actinide's fundamental chemistry have important implications both for the development of new nuclear fuel and for the nuclear fuel reprocessing. One of the major issues in these processes is the ease of uranium to undergo redox reactions and to form polynuclear assemblies, which largely perturb these processes. However, despite their relevance, only few synthetic routes towards polynuclear uranium assemblies are described in the literature, and most of the polynuclear complexes reported are formed by serendipity rather than by rational design. Moreover, polynuclear uranium compounds are highly promising for the design of magnetic materials with improved properties and for reactivity studies. The aim of this work is the synthesis of polynuclear uranium complexes and the study of their reactivity and coordination properties. New synthetic routes to uranium polynuclear assemblies were developed and the study of their physico-chemical properties was carried out. The first approach investigated was based on pentavalent uranyl chemistry. Uranyl(V) is known to form aggregates via an interaction between uranyl moieties often named cation-cation interaction, but the isolation of uranyl(V) complexes had been largely limited by its ease of disproportionation. We isolated the first stable uranyl(V) polynuclear assembly using salen-type Schiff base ligand. Based on this result, a fine tuning of the ligand and counterion properties resulted in the isolation of a large family of uranyl(V) polynuclear assemblies and in a better understanding of the parameters ruling their stability. Moreover, rare examples of clear antiferromagnetic couplings were observed with these complexes. In addition, this synthetic path was used to build the first 5f-3d cluster presenting single molecule magnet properties. The second approach used in this thesis consisted in the synthesis of oxo/hydroxo uranium clusters. The controlled hydrolysis of trivalent uranium in presence of an environmentally relevant ligand lead to the synthesis of clusters, which size could be varied in function of the reaction conditions employed. Finally, new uranium clusters with original topologies were synthesised through the induced disproportionation of pentavalent uranyl precursors.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Computational Design for Metal Organic Responsive Frameworks (MORFs)

Metal organic Frameworks (MOFs) that experience stimuli induced structural transformation could enable a whole new class of materials with remarkable properties. Photoactuating moieties in the structure could effect changes in the pore space or macroscale shape change enabling light driven gas separation and actuators. Here, we present a novel approach based on using graph grammars that makes the problem of discovering MOFs for specific applications amenable to powerful artificial intelligence tree search algorithms. We develop methods for rapidly evaluating MOFs for structural transitions. We will show how this approach may be used to computationally search for candidate MOFs that undergo reversible stimuli induced structural transformation

Uranyl and/or Rare-Earth Mellitates in Extended Organic–Inorganic Networks: A Unique Case of Heterometallic Cation–Cation Interaction with U^VIO–Ln^III Bonding (Ln = Ce, Nd)

A series of uranyl and lanthanide (trivalent Ce, Nd) mellitates (<i>mel</i>) has been hydrothermally synthesized in aqueous solvent. Mixtures of these 4f and 5f elements also revealed the formation of a rare case of lanthanide–uranyl coordination polymers. Their structures, determined by XRD single-crystal analysis, exhibit three distinct architectures. The pure lanthanide mellitate Ln₂(H₂O)₆(<i>mel</i>) possesses a 3D framework built up from the connection of isolated LnO₆(H₂O)₃ polyhedra (tricapped trigonal prism) through the mellitate ligand. The structure of the uranyl mellitate (UO₂)₃(H₂O)₆(<i>mel</i>)·11.5H₂O is lamellar and consists of 8-fold coordinated uranium atoms linked to each other through the organic ligand giving rise to the formation of a 2D 3⁶ net. The third structural type, (UO₂)₂Ln­(OH)­(H₂O)₃(<i>mel</i>)·2.5H₂O, involves direct oxygen bondings between the lanthanide and uranyl centers, with the isolation of a heterometallic dinuclear motif. The 9-fold coordinated Ln cation, LnO₅(OH)­(H₂O)₃, is linked to the 7-fold coordinated uranyl (UO₂)­O₄(OH) (pentagonal bipyramid) via one μ₂-hydroxo group and one μ₂-oxo group. The latter is shared between the uranyl bonding (UO = 1.777(4)/1.779(6) Å) and a long Ln–O bonding (Ce–O = 2.822(4) Å; Nd–O = 2.792(6) Å). This unusual linkage is a unique illustration of the so-called cation–cation interaction associating 4f and 5f metals. The dinuclear motif is then further connected through the mellitate ligand, and this generates organic–inorganic layers that are linked to each other via discrete uranyl (UO₂)­O₄ units (square bipyramid), which ensure the three-dimensional cohesion of the structure. The mixed U–Ln carboxylate is thermally decomposed from 260 to 280 °C and then transformed into the basic uranium oxide (U₃O₈) together with U–Ln oxide with the fluorite structural type (“(Ln,U)­O₂”). At 1400 °C, only fluorite type “(Ln,U)­O₂” is formed with the measured stoichiometry of U_0.63Ce_0.37O₂ and U_0.60Nd_0.40O_2−δ

Uranyl and/or Rare-Earth Mellitates in Extended Organic–Inorganic Networks: A Unique Case of Heterometallic Cation–Cation Interaction with U^VIO–Ln^III Bonding (Ln = Ce, Nd)

A series of uranyl and lanthanide (trivalent Ce, Nd) mellitates (<i>mel</i>) has been hydrothermally synthesized in aqueous solvent. Mixtures of these 4f and 5f elements also revealed the formation of a rare case of lanthanide–uranyl coordination polymers. Their structures, determined by XRD single-crystal analysis, exhibit three distinct architectures. The pure lanthanide mellitate Ln₂(H₂O)₆(<i>mel</i>) possesses a 3D framework built up from the connection of isolated LnO₆(H₂O)₃ polyhedra (tricapped trigonal prism) through the mellitate ligand. The structure of the uranyl mellitate (UO₂)₃(H₂O)₆(<i>mel</i>)·11.5H₂O is lamellar and consists of 8-fold coordinated uranium atoms linked to each other through the organic ligand giving rise to the formation of a 2D 3⁶ net. The third structural type, (UO₂)₂Ln­(OH)­(H₂O)₃(<i>mel</i>)·2.5H₂O, involves direct oxygen bondings between the lanthanide and uranyl centers, with the isolation of a heterometallic dinuclear motif. The 9-fold coordinated Ln cation, LnO₅(OH)­(H₂O)₃, is linked to the 7-fold coordinated uranyl (UO₂)­O₄(OH) (pentagonal bipyramid) via one μ₂-hydroxo group and one μ₂-oxo group. The latter is shared between the uranyl bonding (UO = 1.777(4)/1.779(6) Å) and a long Ln–O bonding (Ce–O = 2.822(4) Å; Nd–O = 2.792(6) Å). This unusual linkage is a unique illustration of the so-called cation–cation interaction associating 4f and 5f metals. The dinuclear motif is then further connected through the mellitate ligand, and this generates organic–inorganic layers that are linked to each other via discrete uranyl (UO₂)­O₄ units (square bipyramid), which ensure the three-dimensional cohesion of the structure. The mixed U–Ln carboxylate is thermally decomposed from 260 to 280 °C and then transformed into the basic uranium oxide (U₃O₈) together with U–Ln oxide with the fluorite structural type (“(Ln,U)­O₂”). At 1400 °C, only fluorite type “(Ln,U)­O₂” is formed with the measured stoichiometry of U_0.63Ce_0.37O₂ and U_0.60Nd_0.40O_2−δ

Synthesis of Coordination Polymers of Tetravalent Actinides (Uranium and Neptunium) with a Phthalate or Mellitate Ligand in an Aqueous Medium

International audienc

Series of hydrated heterometallic uranyl-cobalt(II) coordination polymers with aromatic polycarboxylate ligands: Formation of U=O&mdash;Co bonding upon dehydration process

Five new heterometallic UO22+-Co2+ coordination polymers have been obtained by hydrothermal reactions of uranyl nitrate and metallic cobalt with aromatic polycarboxylic acids. Single-crystal X-ray diffraction reveals the formation of four 3D frameworks with the mellitate (noted mel) ligand and one 2D network with the isophthalate (noted iso) ligand. The compounds [(UO2(H2O))2Co(H2O)4(mel)]·4H2O (1), [UO2Co(H2O)4(H2mel)]·2H2O (2), and [(UO2(H2O))2Co(H2O)4(mel)] (4) consist of 3D frameworks built up from the connection of mellitate ligands and mononuclear metallic centers. These three compounds exhibit two types of geometry for the uranyl cation: pentagonal bipyramidal environment for 1 and 4, and hexagonal bipyramidal environment for 2. Using the mellitate ligand, the uranyl dinuclear unit is isolated in the compound [(UO2)2(OH)2(Co(H2O)4)2(mel)]·2H2O (3). Due to their 2D framework and the presence of uncoordinated cobalt(II) cations, the compound [(UO2)(iso)3][Co(H2O)6]·3(H2O) (5) is drastically different than the previous one. The thermal behavior of compounds 1, 2, and 3 has been studied by thermogravimetric analysis, X-ray thermodiffraction, and in situ infrared. By heating, the dehydration of compounds 1 and 2 promotes two structural transitions (1 → 1′ and 2 → 2′). The crystal structures of [(UO2(H2O))2Co(H2O)2(mel)] (1′) and [(UO2)Co(H2mel)] (2′) were determined by single-crystal X-ray diffraction; each of them presents a heterometallic interaction between uranyl bond and the Co(II) center. Due to the rarely reported coordination environment for the cobalt center in compound 2′ (square pyramidal configuration), the magnetic properties and EPR characterizations of the compounds 2 and 2′ were also investigated