25 research outputs found
Coordination polymers : trapping of radionuclides and chemistry of tetravalent actinides (Th, U) carboxylates
Lâutilisation de lâĂ©nergie nuclĂ©aire pose la question de la prise en compte des radionuclĂ©ides avec lâenvironnement. Actuellement, leur mitigation est un enjeu majeur de la chimie associĂ©e au domaine du nuclĂ©aire. Ce travail de thĂšse a suivi deux axes de recherche : le piĂ©geage des radionuclĂ©ides par une famille de solides poreux Metal-Organic Frameworks (MOF) et la cristallochimie des carboxylates dâactinides tĂ©travalents. La maitrise de cette derniĂšre pourrait permettre de faciliter lâĂ©tude de la spĂ©ciation des actinides dans lâenvironnement. Un intĂ©rĂȘt particulier a Ă©tĂ© portĂ© sur la capture de lâiode dans des MOF Ă base dâaluminium, avec la mise en Ă©vidence de fonctionnalitĂ©s (donneur dâĂ©lectron) qui favorise son piĂ©geage. Les capacitĂ©s dâencapsulation dâactinides lĂ©gers (Th et U) dans les MOF et leur stabilitĂ© sous irradiation Îł ont Ă©galement Ă©tĂ© investiguĂ©s. ParallĂšlement, plus de vingt nouveaux carboxylates dâactinides tĂ©travalents (U et Th) ont Ă©tĂ© caractĂ©risĂ©s par DRX sur monocristal. Certains dâentre eux, prĂ©parĂ©s par hydrolyse contrĂŽlĂ©e en condition solvothermale, sont construits Ă partir dâassemblages polynuclĂ©aires ([U4], [Th6], [U6] et [U38]). Afin de comprendre la formation de ces assemblages, lâĂ©tude ex-situ (DRX, EXAFS, RMN, SEM) de la synthĂšse du composĂ© {U38} a Ă©tĂ© menĂ©e.The use of nuclear energy obviously raises the question of the presence of radionuclides in the environment. Currently, their mitigation is a major issue associated with nuclear chemistry. This thesis focuses on both the trapping of radionuclides by porous solids called Metal-Organic Frameworks (MOF) and the crystal chemistry of the carboxylate of tetravalent actinides (AnIV). The academic knowledge of the reactivity of carboxylate of AnIV could help the understanding of actinides speciation in environment. We focused on the sequestration of iodine by aluminum based MOF. The functionalization (electron-donor group) of the MOF drastically enhances the iodine capture capacity. The removal of light actinides (Th and U) from aqueous solution was also investigated as well as the stability of (Al)-MOF under Îł radiation. More than twenty coordination polymers based on tetravalent actinides have been synthesized and characterized by single crystal X-ray diffraction. The use of controlled hydrolysis promotes the formation of coordination polymers exhibiting polynuclear cluster ([U4], [Th6], [U6] and [U38]). In order to understand the formation of the largest cluster, the ex-situ study of the solvothermale synthesis of compound {U38} has also been investigated
Cyclodextrins as Supramolecular Complexing Agents for Elusive Inorganic Molecular Building Blocks
International audienc
Host-Guest Self-Assembly Between Cyclodextrins and Keggin-Type Polyoxometalates: Driving Forces and Prospects for Future Applications
International audienc
Cyclodextrin-Driven Formation of Double Six-Ring (D6R) Silicate Cage: NMR Spectroscopic Characterization from Solution to Crystals
Identification and isolation of secondary building units (SBUs) from synthesis media of zeolites still represent a challenging task for chemists. The cage structure anion Si12O3012− known as the double six-ring (D6R) was synthesized from α-cyclodextrin (α-CD) mediated alkaline silicate solutions and conditions of its stability and reactivity in aqueous solution were studied by using nuclear magnetic resonance (NMR) spectroscopy. A single crystal X-ray diffraction (XRD) analysis revealed a novel polymorph of the hybrid complex K12Si12O30·2α-CD·nD2O (n ≈ 30⁻40), which crystallizes in the orthorhombic C2221 space group symmetry with a = 14.841(4) Å, b = 25.855(6) Å, and c = 41.91(1) Å. The supramolecular adduct of the silicate anion sandwiched by two α-CDs forms a perfect symmetry matching the H-bonding donor-acceptor system between the organic macrocycle and the D6R unit. The driving force of such a hybrid assembly has found to be strongly dependent on the nature of the cation present as large alkali counter ions (K+, Rb+ and Cs+), which stabilize the D6R structure acting as templates. Lastly, we provided the first 29Si MAS NMR measurement of 3Q Si in an isolated D6R unit that allows the verification of the linear correlation between the chemical shift and <SiOSi> bond angle for 3Q Si species in DnR cages (n = 3, 4, 6)
NMR spectroscopy to study cyclodextrin-based host-guest assemblies with polynuclear clusters
International audienceNatural cyclodextrin (CD) macrocycles are known to form diverse inclusion complexes with a wide variety of organic molecules, but recent work has revealed that inorganic clusters also form multicomponent supramolecular complexes and edifices. Such molecular assemblies exhibit a high degree of organization in solution governed by various chemical processes including molecular recognition, host-guest attraction, hydrophobic repulsion, or chaotropic effect. Nuclear magnetic resonance (NMR) spectroscopy is one of the most efficient and practical analytical techniques to characterize the nature, the strength and the mechanism of these interactions in solution. This review provides a brief overview on recent examples of the contribution of NMR to the characterization of hybrid systems in solution based on CD with polynuclear clusters, including polyoxometalates (POMs), metallic clusters and hydroborate clusters. The focus will be first on using 1H (and 13C) NMR of the host, i.e., CD, to identify the nature of the interactions and measure their strength. Then, 2D NMR methods will be illustrated by DOSY as a means of highlighting the clustering phenomena, and by NOESY/ROESY to evidence the spatial proximity and contact within the supramolecular assemblies. Finally, other NMR nuclei will be selected to probe the inorganic part as a guest molecule. Attention will be paid to classical host-guest complexes Cluster@CD, but also to hierarchical multi-scale, multi-component assemblies such as Cluster@CD@Cluster
Clustering Six Electrons within âDawson-Likeâ Polyoxometalate: An Open Route toward Its Post-functionalization
International audienceSuper-reduction of polyoxometalates (POMs) in solution is of fundamental interest for designing innovative energy storage systems. In this article, we show that the âDawson-likeâ POM can undergo a disproportionation process during its massive electron uptake, leading to species containing three metal-metal bonds as evidenced by X-ray diffraction, multi-nuclear magnetic resonance spectroscopy (1H and 183W NMR), extended X-ray absorption fine structure (EXAFS), UV/Vis, and voltammetry techniques. This result indicates that electron storing within metal-metal bonds is not a unique property of Keggin-type POM as postulated since the 70s. Besides, we demonstrate that the presence of an electron-rich triad in the âDawson-likeâ POM allows its post-functionalization with additional tungstate ions, generating a chiral molecule that is also the largest WIV-containing POMs known to date
Capture of actinides (Th4+, [UO2]2+) and surrogating lanthanide (Nd3+) in the porous Metal-Organic Framework MIL-100(Al) from water : selectivity and imaging of embedded nanoparticles
International audienc
Supramolecular Hybrid Networks Based on Polyoxometalates and Cyclodextrins
International audienc
Supramolecular assemblies of polyoxometalates and metal clusters with cyclodextrins: from inclusion complexes to composite materials
International audienc