1,721,063 research outputs found
Structural investigation of Lanthanoid Coordination: a combined XAS and Molecular Dynamics study
Full text linkUsing a combined theoretical and experimental approach to understand the structure and dynamics of imidazolium-based ionic liquids/water mixtures. 1. MD simulations
No full textThe structural and dynamic properties of 1-butyl-3-methylimidazolium bromide ([C4mim]Br)/water mixtures with different molar ratios have been investigated using classical molecular dynamics (MD) simulations, and the reliability of the results has been assessed by comparison with extended X-ray absorption fine structure experimental data. The analysis of the MD trajectories has highlighted the presence of a complex network of interactions among cations, anions, and water molecules, even if water molecules have been found to interact preferentially with the Br- anion. The existence of solvent-shared ion pairs has been detected in all of the investigated mixtures with one or more water molecules acting as a bridge between the cation and the anion, also when water is present in great excess ([C4mim]Br/water ratio of 1:200). The dynamic behavior of the systems has been characterized starting from the MD trajectories. Water molecules have been found to quicken the dynamics of the IL cations and anions, and acceleration involves all of the investigated motions. © 2013 American Chemical Society
X-ray absorption spectroscopy study of the solvation structure of zinc(II) in dimethyl sulfoxide solution Context Sensitive Links Context Sensitive Links
No full textThe solvation structure of the zinc(II) ion in dimethyl sulfoxide has been determined by studying both the EXAFS and XANES regions of the Zn K-edge absorption spectra. The combination of these two techniques has proved to be very powerful for the complete structural determination of the solvated complex in DMSO solution. The comparison between the experimental and theoretical data has demonstrated that the solvation sphere of the zinc(II) cation is formed by six dimethyl sulfoxide molecules arranged in an octahedral fashion with a Zn-O first shell distance of 2.10(3) angstrom and a Zn-O-S angle close to 120 degrees. (c) 2010 Elsevier B. V. All rights reserved
X-ray absorption study of the solvation structure of Cu 2+ in methanol and dimethyl sulfoxide
No full textThe solvation structure of Cu 2+ in methanol (MeOH) and dimethyl sulfoxide (DMSO) has been determined by studying both the extended X-ray absorption fine structure (EXAFS) and the X-ray absorption near-edge structure (XANES) regions of the K-edge absorption spectra. The EXAFS technique has been found to provide a very accurate determination of the next-neighbor coordination distances, but it is inconclusive in the determination of the coordination numbers and polyhedral environment. Conversely, quantitative analysis of the XANES spectra unambiguously shows the presence of an average 5-fold coordination in both the MeOH and DMSO solution, ruling out the usually proposed octahedral Jahn-Teller distorted geometry. The EXAFS and XANES techniques provide coherent values of the Cu-O first-shell distances that are coincident in the two solvents. This investigation shows that the combined analysis of the EXAFS and XANES data allows a reliable determination of the structural properties of electrolyte solutions, which is very difficult to achieve with other experimental techniques. © 2012 American Chemical Society
Structural characterization of ionic liquids by X-ray absorption spectroscopy
No full textIn this chapter we will illustrate the advantages of X-Ray absorption spectroscopy (XAS) in the structural investigation of ionic liquids (ILs). The combination of a large range of organic cation and anion pairs makes possible to design an enormous number of ILs with specific properties. The characterization of structures in solution is usually elusive and very difficult to be obtained from the standard experimental techniques. With regards to studies of dilute solutions XAS spectroscopy is the structural probe of choice; due to its intrinsic chemical specificity and short range sensitivity this technique measures a less complex correlation function as compared to X-Ray and neutron diffraction that contains very accurate structural information on the short-range distances. This technique can be applied both to the solid and liquid state thus allowing the investigation of ILs in both aggregation states
Effect of the Zn2+ and Hg2+ Ions on the Structure of Liquid Water
No full textThe effect of ions on the structure of liquid water is still not completely understood, despite extensive experimental and theoretical studies. A combined XANES and molecular dynamics investigation on diluted Zn2+ and Hg2+ aqueous solutions reveals that the influence of a single ion on the bonding pattern of water molecules is strongly dependent on the nature of the ion. While the structure of water is not altered by the presence of the Zn2+ ion, the Hg2+ cation has a strong impact on the hydrogen-bond network of water that extends beyond the first coordination shell
Measurement of x-ray multielectron photoexcitations at the I- K edge
No full textWe report the direct measurement by x-ray-absorption spectroscopy of the complete spectrum of multielectron
excitations at the I− K edge. The photoabsorption cross section of crystalline tetramethylammonium iodide
was measured at 28, 50, and 150 K, and room temperature. The latter spectrum has been found to be largely
dominated by the opening of multielectron excitation channels, thus providing a very good model of the I−
atomic background which can be used in the analysis of ionic iodine compounds. Features due to the simultaneous
excitations 1s5p, 1s5s, 1s4d, 1s4p, 1s4s, 1s3d, and 1s3p have been recognized, and their identification
is supported by previous experimental and theoretical determinations on Xe and HI
On the possibility of using XANES to investigate bromide-based ionic liquids
No full textX-ray absorption near edge structure (XANES) spectra have been collected for 1-alkyl-3-methylimidazolium bromide [C(n)mim]Br ILs with different alkyl chains (n = 2, 4). The XANES technique has been found to be sensitive to the subtle differences in the Br coordination environment present in [C(2)mim]Br and [C(4)mim]Br ILs, that are solid at room temperature. With this Letter we show that XANES is a new effective tool for studying the local structural arrangements around selected atoms in ILs both in the solid and liquid phase. (C) 2013 Elsevier B.V. All rights reserved
Using a combined theoretical and experimental approach to understand the structure and dynamics of imidazolium-based ionic liquids/water mixtures. 2. EXAFS spectroscopy
No full textExtended X-ray absorption fine structure (EXAFS) spectroscopy is employed, in conjunction with molecular dynamics (MD) simulations, to investigate the interaction of water with the Br- ion in an imidazolium-based ionic liquid (IL). 1-Butyl-3-methylimidazolium bromide/water mixtures with molar ratios ranging from 1:3 to 1:200 have been analyzed, and a clear picture of the structural arrangements of the water molecules inside the IL has been obtained from the synergic interpretation of the EXAFS and MD data. At the lowest investigated water content, the presence of water is mainly detected around the Br- anion. Upon increasing the water fraction, more water molecules enter the Br- first-coordination shell but always in a lower number than what is needed to saturate the inner sphere. This suggests that interactions also exist between water and the imidazolium cation. The existence of tight ion pairs has been evidenced, even when water is present in the mixtures in great excess. © 2013 American Chemical Society
Analysis of the Detailed Configuration of Hydrated Lanthanoid(III) Ions in Aqueous Solution and Crystalline Salts by Using K- and L-3-Edge XANES Spectroscopy
No full textThe structural properties of the hydrated lanthanoid(III) ions in aqueous solution and in the isostructural trifluoromethanesulfonate salts have been investigated by a quantitative analysis of the X-ray absorption near-edge structure (XANES) spectra at the K- and L-3-edges. The XANES analysis has provided a clear description of the variation of lanthanoid(III) hydration properties across the series. It was found that all of the lanthanoid(III) hydration complexes retain a tricapped trigonal prism (TTP) geometry, and along the series two of the capping water molecules become less and less strongly bound. before finally, oil average, one of them leaves the hydration cluster. This gives rise to an eight-coordinated distorted bicapped trigonal prism with two different Ln-O capping distances for the smallest lanthanoid(111) ions. This systematic study has shown that for lanthanoid compounds more accurate structural information is obtained from the analysis of the L-3-edge than from K-edge XANES data. Moreover. whereas the second hydration shells provide a detectable contribution to the L-3-edge XANES spectra of the lighter lanthanoid ions, the Kedge spectra are insensitive to the more distant coordination spheres
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