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X-ray absorption spectroscopy (XAS) has been employed to carry out structural characterization of the local environment around mercury after the dissolution of the HgCl2 molecule. A combined EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) data analysis has been performed on the Hg L3-edge absorption spectra recorded on 0.1 M HgCl2 solutions in water, methanol (MeOH), acetone and acetonitrile. The Hg–Cl distance determined by EXAFS (2.29(2)–2.31(2) Å) is always comparable to that found in the HgCl2 crystal (2.31(2) Å), demonstrating that the HgCl2 molecule dissolves in these solvents without dissociating. A small sensitivity of EXAFS to the solvent molecules interacting with HgCl2 has been detected and indicates a high degree of configurational disorder associated with this contribution. XANES data analysis, which is less affected by the disorder, was therefore carried out for the first time on these systems to shed light into the still elusive structural arrangement of the solvent molecules around HgCl2. The obtained results show that, in aqueous and MeOH solutions, the XANES data are compatible with three solvent molecules arranged around the HgCl2 unit to form a trigonal bipyramidal structure. The determination of the three-body Cl–Hg–Cl distribution shows a certain degree of uncertainty around the average 180° bond angle value, suggesting that the HgCl2 molecule probably vibrates in the solution around a linear configuration. [ABSTRACT FROM AUTHOR]

The satisfactory rationalization of complex reactive pathways in solution chemistry may greatly benefit from the combined use of advanced experimental and theoretical complementary methods of analysis. In this work, we combine X‐Ray Absorption and 1H NMR spectroscopies with state‐of‐the‐art Multivariate Curve Resolution and theoretical analyses to gain a comprehensive view on a prototypical reaction involving the variation of the oxidation state and local structure environment of a selected metal ion coordinated by organic ligands. Specifically, we investigate the 2‐cyano‐2‐phenylpropanoic acid reduction of the octahedral complex established by the Cu2+ ion with terpyridine to the tetrahedral complex formed by Cu+ and neocuproine. Through our interdisciplinary approach we gain insights into the nature, concentration time evolution and structures of the key metal (XAS measurements) and organic (1H NMR measurements) species under reaction. We believe our method may prove to be useful in the toolbox necessary to understand the mechanisms of reactive processes of interest in solution. [ABSTRACT FROM AUTHOR]

Magnesium chloride is a prototypical deliquescent material whose surface properties, although central for Ziegler-Natta cataysis, have so far remained elusive to experimental characterization. In this work, we use surface-selective X-ray absorption spectroscopy (XAS) at ambient pressure in combination with multivariate curve resolution, molecular dynamics, and XAS theoretical methods to track in real time and accurately describe the interaction between water vapor and the MgCl 2 surface. By exposing MgCl 2 to water vapor at temperatures between 595 and 391 K, we show that water is preferentially adsorbed on five-coordinated Mg 2+ sites in an octahedral configuration, confirming previous theoretical predictions, and find that MgCl 2 is capable of retaining a significant amount of adsorbed water even under prolonged heating to 595 K. As a consequence, our work provides first experimental insights into the unique surface affinity of MgCl 2 for atmospheric water. The developed technique is proven highly sensitive to the modifications induced by adsorbates on a given low-Z metal based surface and may be useful in the toolbox required to disentangle the mechanisms of interfacial chemical processes.

Interfaces between water and materials are ubiquitous and are crucial in materials sciences and in biology, where investigating the interaction of water with the surface under ambient conditions is key to shedding light on the main processes occurring at the interface. Magnesium oxide is a popular model system to study the metal oxide-water interface, where, for sufficient water loadings, theoretical models have suggested that reconstructed surfaces involving hydrated Mg 2+ metal ions may be energetically favored. In this work, by combining experimental and theoretical surface-selective ambient pressure X-ray absorption spectroscopy with multivariate curve resolution and molecular dynamics, we evidence in real time the occurrence of Mg 2+ solvation at the interphase between MgO and solvating media such as water and methanol (MeOH). Further, we show that the Mg 2+ surface ions undergo a reversible solvation process, we prove the dissolution/redeposition of the Mg 2+ ions belonging to the MgO surface, and we demonstrate the formation of octahedral [Mg(H 2 O) 6 ] 2+ and [Mg(MeOH) 6 ] 2+ intermediate solvated species. The unique surface, electronic, and structural sensitivity of the developed technique may be beneficial to access often elusive properties of low-Z metal ion intermediates involved in interfacial processes of chemical and biological interest.

X-ray absorption spectroscopy (XAS) has been employed to carry out structural characterization of the local environment around mercury after the dissolution of the HgCl 2 molecule. A combined EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) data analysis has been performed on the Hg L 3 -edge absorption spectra recorded on 0.1 M HgCl 2 solutions in water, methanol (MeOH), acetone and acetonitrile. The Hg-Cl distance determined by EXAFS (2.29(2)-2.31(2) Å) is always comparable to that found in the HgCl 2 crystal (2.31(2) Å), demonstrating that the HgCl 2 molecule dissolves in these solvents without dissociating. A small sensitivity of EXAFS to the solvent molecules interacting with HgCl 2 has been detected and indicates a high degree of configurational disorder associated with this contribution. XANES data analysis, which is less affected by the disorder, was therefore carried out for the first time on these systems to shed light into the still elusive structural arrangement of the solvent molecules around HgCl 2 . The obtained results show that, in aqueous and MeOH solutions, the XANES data are compatible with three solvent molecules arranged around the HgCl 2 unit to form a trigonal bipyramidal structure. The determination of the three-body Cl-Hg-Cl distribution shows a certain degree of uncertainty around the average 180° bond angle value, suggesting that the HgCl 2 molecule probably vibrates in the solution around a linear configuration.

The dissipative translocation of the Zn 2+ ion between two prototypical coordination complexes has been investigated by combining X-ray absorption and 1 H NMR spectroscopy. An integrated experimental and theoretical approach, based on state-of-the-art Multivariate Curve Resolution and DFT based theoretical analyses, is presented as a means to understand the concentration time evolution of all relevant Zn and organic species in the investigated processes, and accurately characterize the solution structures of the key metal coordination complexes. Specifically, we investigate the dissipative translocation of the Zn 2+ cation from hexaaza-18-crown-6 to two terpyridine moieties and back again to hexaaza-18-crown-6 using 2-cyano-2-phenylpropanoic acid and its para -chloro derivative as fuels. Our interdisciplinary approach has been proven to be a valuable tool to shed light on reactive systems containing metal ions that are silent to other spectroscopic methods. These combined experimental approaches will enable future applications to chemical and biological systems in a predictive manner.

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.