Unraveling the solvation geometries of the lanthanum(iii) bistriflimide salt in ionic liquid/acetonitrile mixtures

Coordination Structure of Samarium Diiodide in a Tetrahydrofuran-Water Mixture

Chemoselective reductive conversion of organic and inorganic compounds has been developed by the combination of samarium(II) diiodide (SmI₂) and water. Despite the extensive previous studies to elucidate the role of water in the reactivity of SmI₂, the direct structural data of the reactive Sm²⁺-water complexes, SmI₂(H₂O)_n, in an organic solvent-water mixture have not been reported experimentally so far. Herein, we performed the structure analysis of the Sm²⁺-water complex in tetrahydrofuran (THF) in the presence of water by in situ X-ray absorption spectroscopy using high-energy X-rays (Sm K-edge, 46.8 keV). The analysis revealed the dissociation of the Sm²⁺-I bonds in the presence of ≥ eight equivalents of water in the THF-water mixture. The origin of the peak shift in the UV/visible absorption spectra after the addition of water into SmI₂/THF solution was proposed based on electron transitions simulated with time-dependent density-functional-theory calculations using optimized structures in THF or water. The obtained structural information provides the fundamental insights for elucidating the reactivity and chemoselectivity in the Sm²⁺-water complex system.

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. Differently, the displaced sesamol and choline molecules are solvated by MeOH, which also forms HBs with other MeOH molecules, so that the system arranges itself to keep the overall amount of HBs maximized. SWAXS measurements show that this mechanism is predominant up to MeOH/DES molar ratios of 20-24, while after this ratio value, the scattering profile is progressively diluted in the cosolvent background and decreases toward the signal of pure MeOH. The ability of MeOH to interplay with all of the DES components produces mixtures with neither segregation of the components at nanoscale lengths nor macroscopic phase separation even for high MeOH contents. These findings have important implications for application purposes since the understanding of the pseudophase aggregates formed by a DES with a dispersing cosolvent can help in addressing an efficient extraction procedure.

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

A thorough structural characterization of the La(NO₃)₃ salt dissolved into several mixtures of ethyl ammonium nitrate (EAN) and methanol (MeOH) with EAN molar fraction χ_EAN 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 La³⁺ first solvation shell when moving from pure MeOH to pure EAN. With increasing the ionic liquid content of the mixture, the La³⁺ first-shell complex progressively loses MeOH molecules to accommodate more and more nitrate anions. Except in pure EAN, the La³⁺ ion is always able to coordinate both MeOH and nitrate anions, with a ratio between the two ligands that changes continuously in the entire concentration range. When moving from pure MeOH to pure EAN, the La³⁺ first solvation shell passes from a 10-fold bicapped square antiprism geometry where all the nitrate anions act only as monodentate ligands to a 12-coordinated icosahedral structure in pure EAN where the nitrate anions bind the La³⁺ cation both in mono- and bidentate modes. The La³⁺ solvation structure formed in the MeOH/EAN mixtures shows a great adaptability to changes in the composition, allowing the system to reach the ideal compromise among all of the different interactions that take place into it.

The structural properties of the La(NO₃)₃ salt dissolved into EAN/methanol mixtures were characterized by molecular dynamics and X-ray absorption spectroscopy. The La³⁺ solvation shell undergoes significant changes with increasing the ionic liquid content of the mixture, progressively losing methanol molecules to accommodate more and more nitrate anions. The La³⁺ solvation structure shows great adaptability to composition changes, passing from a 10-fold bicapped square antiprism geometry in pure methanol to a 12-coordinated icosahedral complex in EAN.

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. Conversely, choline-choline, choline-sesamol and sesamol-sesamol interactions are negligible. A more extended interplay between the constituents is observed in reline where, besides the HBs involving the chloride anion, the eutectic formation is favored also by strong choline-urea and urea-urea interactions. The three-dimensional arrangement around the individual components shows that, in the ChCl : sesamol DES, the cholinium cations and the sesamol molecules are packed in such a way to maximize the interactions with the chlorine anion. This structural arrangement may favor the π-π interactions between the sesamol molecules and the aromatic species mediated by the chloride ions, providing an interpretation for the high separation rates previously observed for phenolic DESs towards aromatic compounds.