10 research outputs found

    Carbon Ligands

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    Homogeneous catalysis owes its success, in large part, to the development of a wide range of ligands with well-defined electronic and steric properties, which have thus made it possible to adjust the behavior of many organometallic complexes. However, ligands used in catalysis have long been centered on elements of group 15, and it is only more recently that carbon ligands have proved to be valuable alternatives with the emergence of cyclic diaminocarbenes (NHC).This Special Issue aims to provide a contemporary overview of the advances in carbon ligand chemistry from fundamental aspects to applications

    Hydration and ion pair formation in common aqueous La(III) salt solutions: a Raman scattering and DFT study

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    Raman spectra of aqueous lanthanum perchlorate, triflate (trifluorosulfonate), chloride and nitrate solutions were measured over a broad concentration (0.121–3.050 mol Lˉ¹) range at room temperature (23 °C). A very weak mode at 343 cmˉ¹ with a full width at half height at 49 cmˉ¹ in the isotropic spectrum suggests that the nona-aqua La(III) ion is thermodynamically stable in dilute perchlorate solutions (∼0.2 mol Lˉ¹) while in concentrated perchlorate solutions outer-sphere ion pairs and contact ion pairs are formed. The La³⁺ nona-hydrate was also detected in a 1.2 mol Lˉ¹ La(CF₃SO₃)₃(aq). In lanthanum chloride solutions chloro-complex formation was detected over the measured concentration range from 0.5–3.050 mol Lˉ¹. The chloro-complexes in LaCl₃(aq) are fairly weak and disappear with dilution. At a concentration <0.1 mol Lˉ¹ almost all complexes disappeared. In LaCl₃ solutions, with additional HCl, a series of chloro-complexes of the type [La(OH₂)₉₋nCln]⁺³⁻ⁿ (n = 1–3) were formed. The La(NO₃)₃(aq) spectra were compared with a spectrum of a 0.409 mol Lˉ¹ NaNO₃(aq) and it was concluded that in La(NO₃)₃(aq) over the concentration range from 0.121–1.844 mol Lˉ¹, nitrato-complexes, [La(OH₂)₉₋n-(NO₃)n]⁺³⁻ⁿ (n = 1, 2) were formed. These nitrato-complexes are quite weak and disappear with dilution <0.01 mol Lˉ¹. DFT geometry optimizations and frequency calculations are reported for a lanthanumnona-hydrate with a polarizable dielectric continuum in order to take the solvent into account. The bond distances and angles for the cluster geometry of [La(OH₂)₉]³⁺ with the polarizable dielectric continuum are in good agreement with data from recent structural experimental measurements and high quality simulations. The DFT frequency of the La–O stretching mode at 328.2 cmˉ¹, is only slightly smaller than the experimental one

    ab initio Molecular Dynamics Simulations of Storage Pond Radionuclides and Related ions

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    An important problem in the nuclear power industry in the UK is the reprocessing of the legacy waste storage ponds at Sellafield in Cumbria. Understanding the solvation structure of the ions present in these ponds, as well as the stability of their hydroxide complexes, is vital for effective clean-up. This work used ab initio molecular dynamics (AIMD) to characterise the solvation structure of Mg2+, Ca2+, Sr2+, Cs+, U6+ in the form of uranyl (UO22+), La3+ and Lu3+. These ions have been found in the legacy storage ponds and have previously been studied through gas phase or implicit solvation Density Functional Theory (DFT) methods. The properties of the first solvation shell have been categorised, and when compared to current experimental and computational literature the results are in excellent agreement, justifying the solvation model developed. The understanding of the solvation structure of the ions in the storage ponds has been developed further, with the introduction of hydroxide ions to replicate the storage ponds alkaline conditions. The coordination and bonding of the hydroxide complexes was characterised, as was the proton transfer behaviour, through quantifying the Proton Transfer Events (PTEs) of each system. The introduction of hydroxides generally led to reduction in coordination number and bond length of the first solvation shell. It was found that PTEs were more prevalent away from the central ion of the system and occurred more frequently in the less charge dense ionic systems, where direct hydroxide coordination to the ion is less prevalent. The final focus of the work was a DFT examination of the adsorption of Sr2+ onto a solvated CeO2(111) surface. The results showed a preference for some ion coordination to the surface, which lessened when hydroxide ions were introduced to the solvation model. The aim of this chapter was to investigate the validity of the surface-solvation model using a surface relevant to the nuclear waste disposal problem for use in future AIMD simulations of the fuel pond environment

    Mining Uranium from Seawater: A Coordination Chemistry Approach

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    Poly(acrylamidoxime) fibers are the current state-of-the-art adsorbent for mining uranium from seawater. However, the amidoxime group is not perfectly selective towards the uranyl cation, in particular, competition with transition metal cations remains a major challenge. In order for subsequent generations of chelating polymer adsorbents to be improved, the coordination chemistry of amidoxime-uranyl and -transition metal cation complexes needs to be better understood. While the coordination mode of amidoxime-uranyl complexes has been established in the literature, a number of amidoxime-transition metal cation complex binding motifs can be observed on the Cambridge Structrural Database. Likewise, the formation constants, or log K values, of a number of essential amidoxime-uranyl and -transition metal cation complexes remain largely unresolved due to the wide range of conflicting acid dissociation constants, or pKa [pKa] values, that have been reported for representative acyclic amidoxime ligands in the literature. Therefore, in Chapter 2 we use spectroscopic titrations to resolve the pKa values of acetamidoxime and benzamidoxime. Subsequently, we use those pKa values to develop computational protocols for predicting the pKa values of aqueous oxoacid ligands. In Chapters 3 and 4, we computationally investigate the binding motif of formamidoximate-dioxovanadium(V) and –oxovanadium(IV) complexes, major competing ions in seawater by utilizing density functional theory and wave-function methods in conjunction with continuum solvation calculations. Our investigations of these formamidoximate complexes universally identified the most stable binding motif to be a tautomerically rearranged imino hydroxylamine chelate formed via coordination of the imino nitrogen and hydroxylamine oxygen. In Chapter 5, we build on the design principles acquired in Chapters 2-4 to design a ligand, salicylaldoxime that is more selective towards utanyl than competing transition metal cations. Finally, in Chapter 6 we potentiometrically determine the proton affinity distribution of the classical poly(acrylamidoxime) fiber between pH 2 and pH 10 via the Stable Numerical Solution of the Adsorption Integral Equation Using Splines (SAIUS) algorithm. This work lays the foundation for resolving the metal cation affinity distribution of the poly(acrylamidoxime) fibers, which can aid in improving the uranium selectivity of subsequent generations of chelating polymers

    Annual Report 2015 / Institute for Nuclear Waste Disposal. (KIT Scientific Reports ; 7725)

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    The contributions collected in this report provide a representative overview of the scientific outcome of INE research activities in 2015. The structure of the report follows widely the organization of the institute according to research topics: basic research towards understanding geochemical reactions of radionuclides on a molecular scale and applied studies on radionuclide retention in multi-barrier system under real repository conditions

    Catalytic Water Oxidation Involving Ruthenium Polypyridyl Complexes

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    Light-driven water oxidation occurs in oxygenic photosynthesis in Photosystem II where reductive equivalents are produced to ultimately convert carbon dioxide into carbohydrates. This process effectively stores solar energy in the form of chemical bonds. Water oxidation is a key component in schemes for artificial photosynthesis, such as solardriven water splitting into hydrogen and oxygen... which could provide much needed clean, renewable fuels. The ... cis,cis-[(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+, is the first well characterized molecule known to catalyze water oxidation. It meets the stoichiometric requirements for water oxidation ... by utilizing proton-coupled electron transfer (PCET) reactions in which both electrons and protons are transferred. In the key step, oxidation to the catalytically-active state, [(O)RuVORuV(O)]4+, results in nucleophilic water attack to form the O-O bond, producing a peroxidic complex. The mechanism of blue dimer catalyzed water oxidation has been resolved to its clearest understanding yet, yielding new insights and opportunities for rational catalyst design. Following this foray into the complexities of the blue dimer, a plethora of single-site (one aqua ligand) ruthenium monomers has been developed, each of which are capable of catalytic water oxidation, driven electrochemically or under acidic conditions using Ce(IV) as a sacrificial oxidant. These homogeneous catalysts have been incorporated into devices by the synthesis of their phosphonic acid derivatized analogues to provide stable interfacial attachment to metal oxide surfaces. Low overpotentials for the electrocatalysis of water oxidation have been achieved with high turnover numbers. Furthermore, a strategy for enhancing rates of water oxidation has been developed using a series of kinetically facile electron transfer mediators with varying thermodynamic driving force. Rate enhancements by factors of up to 30 have been obtained in solution and with surface-modified electrodes. An electrochemical kinetic analysis has been applied for homogeneous water oxidation with surface-modified electrodes. The incorporation of catalysts with electron transfer mediators, which have been studied extensively as chromophores for excited state electron transfer reactions, has led to the design and synthesis of assemblies for electrocatalytic water oxidation, providing new insights into their application toward solar energy conversion. Another approach toward assemblies of this kind has been pursued by exploiting the pH dependence of phosphonic acid derivatized complexes by electrostatic association of cationic water oxidation catalysts to deprotonated, anionic redox mediator-chromophore adsorbates on electrode surfaces. This negates the need for difficult synthetic procedures and bridge design for attaching the necessary components for an artificial photosynthetic apparatus

    Annual Report 2010 - Institute for Nuclear Waste Disposal (KIT Scientific Reports ; 7600)

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    Contributions collected in this report provide a representative overview of the scientific outcome of INE research activities in 2009. The structure of the report follows widely the organization of the institute according to research topics: Basic research towards understanding geochemical reactions of radionuclides on a molecular scale and applied studies on radionuclide retention in multi-barrier system under real repository conditions

    High energy density materials based on tetrazole and nitramine compounds

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    Aspects of coordination chemistry / Frank Richard Keene.

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    Includes bibliographical references.1 v. :Thesis (D.Sc.) -- University of Adelaide, Dept. of Chemistry, 199
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