XAS in Liquid Systems

Filipponi, A.; D’Angelo, P.

doi:10.1002/9781118844243.ch25

Cited by 10 publications

(18 citation statements)

References 76 publications

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“…This happens because the EXAFS region is highly affected by the atomic thermal and structural disorder, resulting in a high correlation between the Debye–Waller factor and the coordination number, as both parameters affect the amplitude of the χ( k ) oscillation. 65 , 67 , 68 …”

Section: Resultsmentioning

confidence: 99%

On the Role of Water in the Formation of a Deep Eutectic Solvent Based on NiCl₂·6H₂O and Urea

et al. 2022

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The metal-based deep eutectic solvent (MDES) formed by NiCl 2 ·6H 2 O and urea in 1:3.5 molar ratio has been prepared for the first time and characterized from a structural point of view. Particular accent has been put on the role of water in the MDES formation, since the eutectic could not be obtained with the anhydrous form of the metal salt. To this end, mixtures at different water/MDES molar ratios ( W ) have been studied with a combined approach exploiting molecular dynamics and ab initio simulations, UV–vis and near-infra-red spectroscopies, small- and wide-angle X-ray scattering, and X-ray absorption spectroscopy measurements. In the pure MDES, a close packing of Ni 2+ ion clusters forming oligomeric agglomerates is present thanks to the mediation of bridging chloride anions and water molecules. Conversely, urea poorly coordinates the metal ion and is mostly found in the interstitial regions among the Ni 2+ ion oligomers. This nanostructure is disrupted upon the introduction of additional water, which enlarges the Ni–Ni distances and dilutes the system up to an aqueous solution of the MDES constituents. In the NiCl 2 ·6H 2 O 1:3.5 MDES, the Ni 2+ ion is coordinated on average by one chloride anion and five water molecules, while water easily saturates the metal solvation sphere to provide a hexa-aquo coordination for increasing W values. This multidisciplinary study allowed us to reconstruct the structural arrangement of the MDES and its aqueous mixtures on both short- and intermediate-scale levels, clarifying the fundamental role of water in the eutectic formation and challenging the definition at the base of these complex systems.

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Section: Resultsmentioning

confidence: 99%

On the Role of Water in the Formation of a Deep Eutectic Solvent Based on NiCl₂·6H₂O and Urea

et al. 2022

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“…A re-evaluation of the LAXS data originally reported in ref has been made in light of the results obtained by the MD simulations in this study. The difficulty in obtaining accurate results on metal ion solvation structures in disordered liquid systems is well-known; therefore, we used both the EXAFS and the XANES (X-ray absorption near-edge structure) techniques to obtain a unified picture of the hydration structure. XAS spectroscopy is known to be a very powerful tool for the study of the first shell structure surrounding a metal because of its high sensitivity to the closest environment of the photoabsorber. , The LAXS technique provides vital information about long and diffuse distances not accessible by XAS.…”

Section: Introductionmentioning

confidence: 99%

Elusive Coordination of the Ag⁺ Ion in Aqueous Solution: Evidence for a Linear Structure

et al. 2020

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X-ray absorption spectroscopy (XAS) has been employed to study the coordination of the Ag + ion in aqueous solution. The conjunction of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) data analysis provided results suggesting the preference for a first shell linear coordination with a mean Ag−O bond distance of 2.34(2) Å, different from the first generally accepted tetrahedral model with a longer mean Ag−O bond distance. Ab initio molecular dynamics simulations with the Car−Parrinello approach (CPMD) were also performed and were able to describe the coordination of the hydrated Ag + ion in aqueous solution in very good agreement with the experimental data. The high sensitivity for the closest environment of the photoabsorber of the EXAFS and XANES techniques, together with the long-range information provided by CPMD and large-angle X-ray scattering (LAXS), allowed us to reconstruct the three-dimensional model of the coordination geometry around the Ag + ion in aqueous solution. The obtained results from experiments and theoretical simulations provided a complex picture with a certain amount of water molecules with high configurational disorder at distances comprised between the first and second hydration spheres. This evidence may have caused the proliferation of the coordination numbers that have been proposed so far for Ag + in water. Altogether these data show how the description of the hydration of the Ag + ion in aqueous solution can be complex, differently from other metal species where hydration structures can be described by clusters with well-defined geometries. This diffuse hydration shell causes the Ag−O bond distance in the linear [Ag(H 2 O) 2 ] + ion to be ca. 0.2 Å longer than in isolated ions in solid state.

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“… 37 − 43 In this respect, due to its unique short-range sensitivity and chemical selectivity, the X-ray absorption spectroscopy (XAS) technique is an ideal candidate to provide accurate structural information on the local arrangement of the solvent molecules around a metal ion. 44 , 45 In particular, the combination between XAS and molecular dynamics (MD) simulations provides an invaluable tool for the structural characterization of metal ion solutions in ILs. 36 , 46 − 48 Through the synergic use of the XAS and MD techniques, one can also check the validity of the level of theory employed in the simulations directly on the experimental evidence, while having at the same time a reliable structural model to be used in the analysis of the experimental data.…”

Section: Introductionmentioning

confidence: 99%

“…For example, the thermodynamic parameters obtained in some studies on the formation of Ni 2+ complexes with dimethyl sulfoxide, methanol, and acetonitrile in 1-alkyl-3-methylimidazolium ([C n mim]) bis(trifluoromethylsulfonyl)imide ([Tf 2 N] − ) ILs (where C n is the length of the alkyl chain, in this work n = 2, 8) , and with nitrate in [C 4 mim][Tf 2 N] could be reinterpreted if the coordination geometry of the starting solvated metal ions was established. However, the structural characterization of metal ion solvation complexes in disordered liquid samples is known to be a difficult task. − In this respect, due to its unique short-range sensitivity and chemical selectivity, the X-ray absorption spectroscopy (XAS) technique is an ideal candidate to provide accurate structural information on the local arrangement of the solvent molecules around a metal ion. , In particular, the combination between XAS and molecular dynamics (MD) simulations provides an invaluable tool for the structural characterization of metal ion solutions in ILs. ,− Through the synergic use of the XAS and MD techniques, one can also check the validity of the level of theory employed in the simulations directly on the experimental evidence, while having at the same time a reliable structural model to be used in the analysis of the experimental data.…”

Section: Introductionmentioning

confidence: 99%

Coordination of the Co²⁺ and Ni²⁺ Ions in Tf₂N^– Based Ionic Liquids: A Combined X-ray Absorption and Molecular Dynamics Study

et al. 2021

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Molecular dynamics (MD) simulations and X-ray absorption spectroscopy (XAS) have been combined to study the coordination of the Co 2+ and Ni 2+ ions in ionic liquids (ILs) based on the bis(trifluoromethylsulfonyl)imide ([Tf 2 N] − ) anion and having different organic cations, namely, 1-butyl-3-methylimidazolium ([C 4 mim] + ), 1,8-bis(3-methylimidazolium-1-yl)octane ([C 8 (mim) 2 ] 2+ ), N , N , N -trimethyl- N -(2-hydroxyethyl)ammonium ([choline] + ), and butyltrimethylammonium ([BTMA] + ). Co and Ni K-edge XAS data have been collected on 0.1 mol L –1 Co(Tf 2 N) 2 and Ni(Tf 2 N) 2 solutions and on the metallic salts. MD simulations have been carried out to obtain structural information on the metal ion coordination. The analysis of the extended X-ray absorption fine structure (EXAFS) spectra of the solutions has been carried out based on the atomistic description provided by MD, and the studied ILs have been found to be able to dissolve both the Co(Tf 2 N) 2 and Ni(Tf 2 N) 2 salts giving rise to a different structural arrangement around the metal ions as compared to the solid state. The combined EXAFS and MD results showed that the Co 2+ and Ni 2+ ions are surrounded by a first solvation shell formed by six [Tf 2 N] − anions, each coordinating in a monodentate fashion by means of the oxygen atoms. The nature of the IL organic cation has little or no influence on the overall spatial arrangement of the [Tf 2 N] − anions, so that stable octahedral complexes of the type [M(Tf 2 N) 6 ] 4– (M = Co, Ni) have been observed in all the investigated ILs.

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XAS in Liquid Systems

Cited by 10 publications

References 76 publications

On the Role of Water in the Formation of a Deep Eutectic Solvent Based on NiCl₂·6H₂O and Urea

On the Role of Water in the Formation of a Deep Eutectic Solvent Based on NiCl₂·6H₂O and Urea

Elusive Coordination of the Ag⁺ Ion in Aqueous Solution: Evidence for a Linear Structure

Coordination of the Co²⁺ and Ni²⁺ Ions in Tf₂N^– Based Ionic Liquids: A Combined X-ray Absorption and Molecular Dynamics Study

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XAS in Liquid Systems

Cited by 10 publications

References 76 publications

On the Role of Water in the Formation of a Deep Eutectic Solvent Based on NiCl2·6H2O and Urea

On the Role of Water in the Formation of a Deep Eutectic Solvent Based on NiCl2·6H2O and Urea

Elusive Coordination of the Ag+ Ion in Aqueous Solution: Evidence for a Linear Structure

Coordination of the Co2+ and Ni2+ Ions in Tf2N– Based Ionic Liquids: A Combined X-ray Absorption and Molecular Dynamics Study

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On the Role of Water in the Formation of a Deep Eutectic Solvent Based on NiCl₂·6H₂O and Urea

On the Role of Water in the Formation of a Deep Eutectic Solvent Based on NiCl₂·6H₂O and Urea

Elusive Coordination of the Ag⁺ Ion in Aqueous Solution: Evidence for a Linear Structure

Coordination of the Co²⁺ and Ni²⁺ Ions in Tf₂N^– Based Ionic Liquids: A Combined X-ray Absorption and Molecular Dynamics Study