A combined soft X-ray and theoretical investigation discloses the water harvesting behaviour of Mg-MOF-74 at the crystal surface.

Metal-organic frameworks (MOFs) are receiving growing interest as transformative materials for real-world atmospheric water harvesting applications. However, obtaining molecular-level details on how surface effects regulate MOF water uptake has proven to be elusive. Here, we present a novel methodology based on ambient pressure soft X-ray absorption spectroscopy (AP-NEXAFS), machine learning-assisted theoretical spectroscopy and molecular dynamics simulations to gain selective insights into the behaviour of water at a MOF crystal surface.

Mercury Monohalides as Ligands in Transition Metal Complexes.

The main categories of transition metal-mercury heterometallic compounds are briefly summarized. The attention is focused on complexes and clusters where the {Hg-Y} fragment, where Y represents a halide atom, interacts with transition metals. Most of the structurally characterized derivatives are organometallic compounds where the transition metals belong to the Groups 6, 8, 9 and 10.

Insight into physico-chemical properties of oxalatoborate-based ionic liquids through combined experimental-theoretical characterization.

Ionic liquids (ILs) including oxalatoborate anions, like bis(oxalato)borate (BOB) and difluoro(oxalato)borate (DFOB) are extensively used in the battery sector as additives to promote the formation of protective layers on the surface of high-voltage cathode materials. In this work four ILs have been synthesized: -ethoxyethyl--methylpiperidinium bis(oxalato)borate (PIPBOB), -ethoxyethyl--methylpiperidinium difluoro(oxalato)borate (PIPDFOB), -propyl--methylpiperidinium bis(oxalato)borate (PIPBOB) and -propyl--methylpiperidinium difluoro(oxalato)borate (PIPDFOB) and their thermal properties have been linked to their structure. The presence of an oxygen atom in the PIP lateral chain suppresses crystallization of the ILs.

On the composition and isomerism effect in the thermal and structural properties of choline chloride/hydroxyphenol deep eutectic solvents.

We have carried out a comparative study on three sets of eutectic mixtures based on choline chloride (ChCl) and hydroxyphenol isomers having two hydroxyl groups in the -, -, and -positions of the aromatic ring, namely catechol (Cate), resorcinol (Reso), and hydroquinone (Hydro), respectively. Differential scanning calorimetry highlighted a different thermal behavior of the mixtures depending on the composition and precursor isomerism. These systems behave as deep eutectic solvents (DESs) with the exception of the ChCl/Cate mixture at a 1 : 0.

In-Depth XANES and EXAFS Characterization of the Ag Ion Coordination in Dimethyl Sulfoxide Solution.

X-ray absorption near-edge structure (XANES) spectroscopy has been used, in conjunction with extended X-ray absorption fine structure (EXAFS), to determine the coordination structure of the Ag ion in a dimethyl sulfoxide (DMSO) solution. From the EXAFS data analysis, the Ag-O first shell distance in DMSO was found to be 2.31(3) Å, with 4.

Investigating the High-Temperature Water/MgCl Interface through Ambient Pressure Soft X-ray Absorption Spectroscopy.

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 surface. By exposing MgCl to water vapor at temperatures between 595 and 391 K, we show that water is preferentially adsorbed on five-coordinated Mg sites in an octahedral configuration, confirming previous theoretical predictions, and find that MgCl is capable of retaining a significant amount of adsorbed water even under prolonged heating to 595 K.

Direct Observation of Contact Ion-Pair Formation in La Methanol Solution.

An approach combining molecular dynamics (MD) simulations and X-ray absorption spectroscopy (XAS) has been used to carry out a comparative study about the solvation properties of dilute La(NO) solutions in water and methanol, with the aim of elucidating the still elusive coordination of the La ion in the latter medium. The comparison between these two systems enlightened a different behavior of the nitrate counterions in the two environments: while in water the La(NO) salt is fully dissociated and the La ion is coordinated by water molecules only, the nitrate anions are able to enter the metal first solvation shell to form inner-sphere complexes in methanol solution. The speciation of the formed complexes showed that the 10-fold coordination is preferential in methanol solution, where the nitrate anions coordinate the La cations in a monodentate fashion and the methanol molecules complete the solvation shell to form an overall bicapped square antiprism geometry.

Caught while Dissolving: Revealing the Interfacial Solvation of the Mg Ions on the MgO Surface.

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 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 solvation at the interphase between MgO and solvating media such as water and methanol (MeOH).

Solubilization and coordination of the HgCl molecule in water, methanol, acetone, and acetonitrile: an X-ray absorption investigation.

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 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-edge absorption spectra recorded on 0.1 M HgCl solutions in water, methanol (MeOH), acetone and acetonitrile.

On the Role of Water in the Formation of a Deep Eutectic Solvent Based on NiCl·6HO and Urea.

The metal-based deep eutectic solvent (MDES) formed by NiCl·6HO 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.

Two Faces of the Same Coin: Coupling X-Ray Absorption and NMR Spectroscopies to Investigate the Exchange Reaction Between Prototypical Cu Coordination Complexes.

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 H 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 Cu ion with terpyridine to the tetrahedral complex formed by Cu and neocuproine.

Fate of a Deep Eutectic Solvent upon Cosolvent Addition: Choline Chloride-Sesamol 1:3 Mixtures with Methanol.

The changes upon methanol (MeOH) addition in the structural arrangement of the highly eco-friendly deep eutectic solvent (DES) formed by choline chloride (ChCl) and sesamol in 1:3 molar ratio have been studied by means of attenuated total reflection Fourier transform infrared spectroscopy, small- and wide-angle X-ray scattering (SWAXS), and molecular dynamics simulations. The introduction of MeOH into the DES promotes the increase of the number of Cl-MeOH hydrogen bonds (HBs) through the replacement of sesamol and choline molecules from the chloride anion coordination sphere. This effect does not promote the sesamol-sesamol, choline-choline, and sesamol-choline interactions, which remain as negligible as in the pure DES.

On the Coordination Chemistry of the lanthanum(III) Nitrate Salt in EAN/MeOH Mixtures.

A thorough structural characterization of the La(NO) salt dissolved into several mixtures of ethyl ammonium nitrate (EAN) and methanol (MeOH) with EAN molar fraction χ ranging from 0 to 1 has been carried out by combining molecular dynamics (MD) and X-ray absorption spectroscopy (XAS). The XAS and MD results show that changes take place in the La first solvation shell when moving from pure MeOH to pure EAN. With increasing the ionic liquid content of the mixture, the La first-shell complex progressively loses MeOH molecules to accommodate more and more nitrate anions.

Coordination of the Co and Ni Ions in TfN Based Ionic Liquids: A Combined X-ray Absorption and Molecular Dynamics Study.

Molecular dynamics (MD) simulations and X-ray absorption spectroscopy (XAS) have been combined to study the coordination of the Co and Ni ions in ionic liquids (ILs) based on the bis(trifluoromethylsulfonyl)imide ([TfN]) anion and having different organic cations, namely, 1-butyl-3-methylimidazolium ([Cmim]), 1,8-bis(3-methylimidazolium-1-yl)octane ([C(mim)]), ,,-trimethyl--(2-hydroxyethyl)ammonium ([choline]), and butyltrimethylammonium ([BTMA]). Co and Ni K-edge XAS data have been collected on 0.1 mol L Co(TfN) and Ni(TfN) solutions and on the metallic salts.

Anatomy of a deep eutectic solvent: structural properties of choline chloride : sesamol 1 : 3 compared to reline.

The structural properties of the deep eutectic solvent (DES) formed by choline chloride (ChCl) and sesamol in 1 : 3 ratio have been investigated and compared to those of reline (ChCl : urea 1 : 2). An integrated approach combining small and wide angle X-ray scattering with molecular dynamics simulations has been employed and the simulation protocol has been validated against the experimental data. In the ChCl : sesamol DES, strong hydrogen bonds (HBs) are formed between the chloride anion and the hydroxyl groups of the choline and of sesamol molecules.

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

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.

Solvation of Zn ion in 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids: a molecular dynamics and X-ray absorption study.

Molecular dynamics (MD) simulations and X-ray absorption spectroscopy (XAS) were employed to study the solvation of Zn2+ ion in dry [Cnmim][Tf2N] (n = 2, 4; 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) room temperature ionic liquids (RTILs). For [C4mim][Tf2N] also a water-saturated system was considered. The thermodynamic parameters of single ion solvation and transfer from water to the RTIL, as well as the structural information, were calculated by means of MD simulations and our study evidences that both structural and thermodynamic features can be reproduced by MD in good agreement with the experimental data.