The Experts below are selected from a list of 93 Experts worldwide ranked by ideXlab platform
Richard Wilson - One of the best experts on this subject based on the ideXlab platform.
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Structural and Electronic Properties of Nb(V), Ta(V), and Pa(V) Fluoride Complexes:The Influence of Relativistic Effects on the Group V Elements
European Journal of Inorganic Chemistry, 2016Co-Authors: Richard Wilson, Stephanie De Sio, Valérie ValletAbstract:The aqueous fluoro complexes of niobium and tantalum were studied using synchrotron based extended X-ray absorption spectroscopy (EXAFS) as model systems for comparison of the structural and coordination chemistry of the Group V metals Nb, Ta and their pseudo-homologue Pa(V). The EXAFS indicate differences in the coordination chemistry of Nb and Ta in these systems that were not intuitive based on their similar charge and ionic radii. The Ta speciation is dominated by six and seven coordinate fluoro complexes, while the chemical speciation of Nb under the same conditions is dominated by its hydrolyzed oxyfluoride complexes. Quantum chemical computations were performed to more fully describe these observations and these results were compared to our earlier study on the fluoro complexes of Protactinium. Computations performed with and without the inclusion of scalar relativistic effects reveal that the differences in the chemistry among the Group V elements, and their pseudo-homologue Protactinium, are due to the increasing influences of relativistic effects as Z is increased from niobium to Protactinium.
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Peculiar Protactinium
Nature Chemistry, 2012Co-Authors: Richard WilsonAbstract:Richard Wilson relates how the rare, highly radioactive, highly toxic element Protactinium puzzled chemists for a long time, and was discovered and named twice from two different isotopes before finding its place in fundamental research.
Stephanie De Sio - One of the best experts on this subject based on the ideXlab platform.
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Protactinium and the intersection of actinide and transition metal chemistry
Nature Publishing Group, 2018Co-Authors: Richard E. Wilson, Stephanie De Sio, Valérie ValletAbstract:The role of the 5f and 6d orbitals in the chemical bonding of the actinide elements remains debated. Here, the authors synthesize and study a tetranuclear Protactinium peroxo cluster and demonstrate that Protactinium represents an intersection of actinide (5f) and transition metal (6d) chemistries
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Structural and Electronic Properties of Nb(V), Ta(V), and Pa(V) Fluoride Complexes:The Influence of Relativistic Effects on the Group V Elements
European Journal of Inorganic Chemistry, 2016Co-Authors: Richard Wilson, Stephanie De Sio, Valérie ValletAbstract:The aqueous fluoro complexes of niobium and tantalum were studied using synchrotron based extended X-ray absorption spectroscopy (EXAFS) as model systems for comparison of the structural and coordination chemistry of the Group V metals Nb, Ta and their pseudo-homologue Pa(V). The EXAFS indicate differences in the coordination chemistry of Nb and Ta in these systems that were not intuitive based on their similar charge and ionic radii. The Ta speciation is dominated by six and seven coordinate fluoro complexes, while the chemical speciation of Nb under the same conditions is dominated by its hydrolyzed oxyfluoride complexes. Quantum chemical computations were performed to more fully describe these observations and these results were compared to our earlier study on the fluoro complexes of Protactinium. Computations performed with and without the inclusion of scalar relativistic effects reveal that the differences in the chemistry among the Group V elements, and their pseudo-homologue Protactinium, are due to the increasing influences of relativistic effects as Z is increased from niobium to Protactinium.
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EXAFS Study of the Speciation of Protactinium(V) in Aqueous Hydrofluoric Acid Solutions
Inorganic chemistry, 2014Co-Authors: Stephanie De Sio, Richard E. WilsonAbstract:The speciation of Protactinium(V) in hydrofluoric acid (HF) solutions was studied using X-ray absorption spectroscopy. Extended X-ray absorption fine structure measurements were performed on an aqueous solution of 0.05 M Protactinium(V) with various HF concentrations ranging from 0.5 to 27 M in order to probe the Protactinium coordination sphere with respect to the identity and number of coordinating ligands. The resulting fits to the spectra suggest the presence of an eight-coordinate homoleptic fluoro complex in highly concentrated fluoride solutions (27 M), with equilibrium between seven- and eight-coordinate fluoro complexes at moderate acidities, and in more dilute solutions, results indicate that one water molecule is likely to replace a fluoride in the first coordination sphere, at a distance of 2.54–2.57 A. Comparisons of this chemistry with group V metals, niobium and tantalum, are presented, and the potential implications for these results on the hydrolytic behavior of Protactinium in aqueous sy...
Richard E. Wilson - One of the best experts on this subject based on the ideXlab platform.
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Protactinium and the intersection of actinide and transition metal chemistry
Nature Publishing Group, 2018Co-Authors: Richard E. Wilson, Stephanie De Sio, Valérie ValletAbstract:The role of the 5f and 6d orbitals in the chemical bonding of the actinide elements remains debated. Here, the authors synthesize and study a tetranuclear Protactinium peroxo cluster and demonstrate that Protactinium represents an intersection of actinide (5f) and transition metal (6d) chemistries
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EXAFS Study of the Speciation of Protactinium(V) in Aqueous Hydrofluoric Acid Solutions
Inorganic chemistry, 2014Co-Authors: Stephanie De Sio, Richard E. WilsonAbstract:The speciation of Protactinium(V) in hydrofluoric acid (HF) solutions was studied using X-ray absorption spectroscopy. Extended X-ray absorption fine structure measurements were performed on an aqueous solution of 0.05 M Protactinium(V) with various HF concentrations ranging from 0.5 to 27 M in order to probe the Protactinium coordination sphere with respect to the identity and number of coordinating ligands. The resulting fits to the spectra suggest the presence of an eight-coordinate homoleptic fluoro complex in highly concentrated fluoride solutions (27 M), with equilibrium between seven- and eight-coordinate fluoro complexes at moderate acidities, and in more dilute solutions, results indicate that one water molecule is likely to replace a fluoride in the first coordination sphere, at a distance of 2.54–2.57 A. Comparisons of this chemistry with group V metals, niobium and tantalum, are presented, and the potential implications for these results on the hydrolytic behavior of Protactinium in aqueous sy...
C. Hennig - One of the best experts on this subject based on the ideXlab platform.
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Thermodynamical and Structural Study of Protactinium(V) Oxalate Complexes in Solution
Inorganic Chemistry, 2010Co-Authors: M. Mendes, C. Le Naour, C. Den Auwer, S. Hamadi, J. Roques, A. Jeanson, P. Moisy, S. Topin, J. Aupiais, C. HennigAbstract:The complexation of Protactinium(V) by oxalate was studied by X-ray absorption spectroscopy (XAS), density functional theory (DFT) calculations, capillary electrophoresis coupled with inductively coupled plasma mass spectrometry (CE-ICP-MS) and solvent extraction. XAS measurements showed unambiguously the presence of a short single oxo-bond, and the deduced structure agrees with theoretical calculations. CE-ICP-MS results indicated the formation of a highly charged anionic complex. The formation constants of PaO(C2O4)+, PaO(C2O4)2−, and PaO(C2O4)33− were determined from solvent extraction data by using Protactinium at tracer scale (CPa < 10−10 M). Complexation reactions of Pa(V) with oxalate were found to be exothermic with relatively high positive entropic variation.
C. Le Naour - One of the best experts on this subject based on the ideXlab platform.
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Thermodynamical and Structural Study of Protactinium(V) Oxalate Complexes in Solution
Inorganic Chemistry, 2010Co-Authors: M. Mendes, C. Le Naour, C. Den Auwer, S. Hamadi, J. Roques, A. Jeanson, P. Moisy, S. Topin, J. Aupiais, C. HennigAbstract:The complexation of Protactinium(V) by oxalate was studied by X-ray absorption spectroscopy (XAS), density functional theory (DFT) calculations, capillary electrophoresis coupled with inductively coupled plasma mass spectrometry (CE-ICP-MS) and solvent extraction. XAS measurements showed unambiguously the presence of a short single oxo-bond, and the deduced structure agrees with theoretical calculations. CE-ICP-MS results indicated the formation of a highly charged anionic complex. The formation constants of PaO(C2O4)+, PaO(C2O4)2−, and PaO(C2O4)33− were determined from solvent extraction data by using Protactinium at tracer scale (CPa < 10−10 M). Complexation reactions of Pa(V) with oxalate were found to be exothermic with relatively high positive entropic variation.
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Speciation of Protactinium(V) at tracer scale
Radiochimica Acta, 2009Co-Authors: C. Le Naour, M. V. Di Giandomenico, Y. Zhao, M. MendesAbstract:Solvent extraction in the conditions of tracer scale chemistry was used to study Protactinium(V) complexation with sulphate, chloride, oxalate and diethylene-triamine-pentaacetate. Extraction experiments were conducted using the chelating agent thenoyltrifluoroacetone (TTA) in toluene at constant ionic strength and temperature. Information on the species involved in partition equilibria relative to Protactinium(V) complexation were deduced from a systematic study of the variations of distribution coefficient of Pa(V) as function of ligands, protons and TTA concentration.
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Structure of early actinides(V) in acidic solutions
Radiochimica Acta, 2009Co-Authors: M. V. Di Giandomenico, C. Le Naour, E. Simoni, D. Guillaumont, Philippe Moisy, Christoph Hennig, Steven D. Conradson, C. Den AuwerAbstract:Protactinium occupies a key position in the actinide series between thorium and uranium. In aqueous acidic solution, it is stable at oxidation state (V), occurring either as an oxocation or as a naked ion, depending on the media. Very few structural information on the hydration sphere of Pa(V) in acidic medium is available, in particular in hydrofluoric acid. Combined EXAFS and theoretical calculations have been used in this work to characterize the Protactinium coordination sphere at various HF concentrations. The correlation of the XAFS data with quantum chemical calculations provides complementary structural and electronic models from ab initio techniques. At HF concentrations from 0.5 to 0.05 M, both theoretical calculations and EXAFS data suggest that the Protactinium coordination sphere is mainly composed of fluoride ions. At the lowest HF concentration, the occurrence of a monooxo bond is observed with EXAFS, in agreement with the literature. A comparison of these data with related neptunium(V) and plutonium(V) diooxocations in perchloric acid is also presented.
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Adsorption behavior of Zr, Hf, Nb, Ta and Pa on macroporous anion exchanger in NH_4SCN/HClO_4 and NH_4SCN/HF media
Journal of Radioanalytical and Nuclear Chemistry, 2002Co-Authors: F. Monroy-guzman, D. Trubert, C. Le NaourAbstract:The possible use of thiocyanate and ammonium thiocyanate-hydrofluoric acid mixtures for quantitative anion exchange separation of zirconium from hafnium and niobium from tantalum and Protactinium has been investigated. Distribution coefficients of zirconium(IV), hafnium(IV), niobium(V), tantalum(V) and Protactinium(V) on macroporous BIO-RAD AGMP1 resin over a wide range of SCN and SCN/HF concentrations have been determined. The simultaneous presence of these two complexing agents causes a strong decrease of the adsorption phenomena.
