1,721,021 research outputs found
Unraveling the Sc3+ hydration geometry: the strange case of the far-coordinated water molecule
No full textThe hydration structure and dynamics of Sc3+ in aqueous solution have been investigated using a combined approach based on quantum mechanical (QM) calculations, molecular dynamics (MD) simulations, and extended X-ray absorption fine structure (EXAFS) spectroscopy. An effective Sc−water two-body potential has been generated from QM calculations and then used in the MD simulation of Sc3+ in water, and the reliability of the entire procedure has been assessed by comparing the theoretical structural results with the EXAFS experimental data. The outstanding outcome of this work is that the Sc3+ ion forms a well-defined capped square antiprism (SAP) complex in aqueous solution, where the eight water molecules closest to the ion are located at the vertexes of a SAP polyhedron, while the ninth water molecule occupying the capping position is unusually found at a very long distance from the ion. This far-coordinated water molecule possesses a degree of structure comparable with the other first shell molecules surrounding the ion at much shorter distances, and its presence gave us the unique opportunity to easily identify the geometry of the Sc3+ coordination polyhedron. Despite very strong ion−water interactions, the Sc3+ hydration shell is very labile, as the far-coordinated ligand allows first shell water molecules to easily exchange their positions both inside the solvation shell and with the rest of the solvent molecules
Deep eutectic solvents: a structural point of view on the role of the anion
Full text linkThe structural properties of four deep eutectic solvents (DESs), namely a 1:2 mixture of choline chloride and urea, and three analogous DESs containing different anions in place of chloride, namely fluoride, nitrate or acetate, were investigated by using Molecular Dynamics. The order of the DES melting points was found not to correlate with the strength of urea-anion hydrogen bonds. However, the DES low melting points are related to the anion ability to build favourable networks of interactions with both choline and urea, in such a way as to maximize the hydrogen bonds among all the different moieties of the system
Unraveling the perturbation induced by Zn2+ and Hg2+ ions on the hydrogen bond patterns of liquid methanol
No full textThe perturbation induced by the Zn2+ and Hg2+ ions on the methanol hydrogen bond patterns has been investigated by means of Molecular dynamics simulations. The methanol structure in the ion second coordination shell has been found to be significantly altered by the presence of both ions, the structuring ability being larger for Zn2+. Remarkable modifications of the hydrogen bond structure and dynamics have been evidenced, and peculiar networks of hydrogen bonds have been highlighted where the methanol molecules act as a bridge between the ion first shell complex and the bulk solvent. © 2015 Elsevier B.V. All rights reserved
A quantum mechanics, molecular dynamics and EXAFS investigation into the Hg2+ ion solvation properties in methanol solution
No full textThe coordination properties of the Hg2+ ion in methanol solution have been investigated by combining extended X-ray absorption fine structure (EXAFS) spectroscopy and Quantum Mechanics/Molecular Dynamics (QM/MD) calculations. An effective Hg-methanol two-body potential has been generated from QM calculations in which the effect of bulk solvent is accounted for by the polarizable continuum model (PCM). This effective potential is then used in the MD simulation to obtain the structural and dynamic properties of the solution, and the reliability of the entire procedure is assessed by comparing the theoretical structural results with the EXAFS experimental data. The outstanding outcome of this work is that the Hg2+ ion forms a stable sevenfold complex in methanol solution, where the first shell solvent molecules are arranged in a distorted pentagonal bipyramid geometry. In this geometry five methanol molecules are not located on the equatorial plane, but are displaced above and below the plane, forming a "crown" around the ion. The Hg2+ first coordination shell has been found to be very flexible, and several transitions among coordination numbers of 7, 8 and 6 are observed during the simulation
Solvation structure of Zn2+ and Cu2+ ions in acetonitrile: a combined EXAFS and XANES study
No full textThe solvation structure of Zn2+ and Cu2+ in acetonitrile has been determined by a combined approach using both X-ray absorption near edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) spectroscopy. For the former cation, an octahedral geometry of the acetonitrile solvate complex has been found with a Zn-N distance of 2.12(1) Å. For the Cu2+ solvates the EXAFS technique has been found to be not able to provide a conclusive determination of the coordination numbers and polyhedral environment, while the analysis of the XANES spectra unambiguously shows the existence of an axially elongated square pyramidal coordination, ruling out the previously proposed octahedral Jahn-Teller (JT) distorted geometry. The Cu-N distances obtained are 2.00(1) and 2.28(2) Å for the equatorial and axial ligands, respectively, and the EXAFS and XANES techniques find values of the bond distances in good agreement. The XANES technique has proven to be extremely powerful in providing a reliable resolution of solution structure for dynamic ion complexes. © 2015 American Chemical Society
Using 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
Unraveling the hydration properties of the Ba2+ aqua ion: the interplay of quantum mechanics, molecular dynamics, and EXAFS spectroscopy
No full textThe structural and dynamic properties of the Ba2+ cation in water have been studied by combining quantum mechanical (QM) calculations, molecular dynamics (MD) simulations, and extended X-ray absorption fine structure (EXAFS) spectroscopy. An effective Ba2+-water interaction potential, to be used in the MD simulation of a Ba2+ aqueous solution, has been developed by means of QM methods, and the validity of the whole procedure has been assessed by comparing the theoretical structural results with the EXAFS experimental data. By combining distance and angular distribution functions it was possible to unambiguously identify the geometry adopted by the water molecules surrounding the ion in the solution. The Ba2+ ion was found to preferentially form an 8-fold first shell complex with a bicapped trigonal prism (BTP) geometry. The 8-fold complex is in equilibrium with a 9-fold structure having a tricapped trigonal prism (TTP) geometry, and the hydration shell is very diffuse and flexible, being characterized by a very fast solvent exchange process on the picosecond time scale
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