Hidden Hydration Structure of Halide Ions: an Insight into the Importance of Lone Pairs

Sessa, Francesco; D’Angelo, P.; Guidoni, Leonardo

doi:10.1021/acs.jpcb.5b10636

Cited by 28 publications

(34 citation statements)

References 49 publications

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“…The exchange process rate has been evaluated by computing the mean residence times of both water molecules ( t WAT (2) ) and anions ( t X (2) ) in the Ln 3+ second coordination sphere (see Table ), by means of the Impey method . Following previous studies, ,,− a t * value of 0.5 ps has been chosen to define a real exchange in the Impey procedure. All of the calculated residence times are of the order of magnitude of picoseconds, thus revealing the flexible nature of the La 3+ second solvation shell.…”

Section: Resultsmentioning

confidence: 99%

Influence of Counterions on the Hydration Structure of Lanthanide Ions in Dilute Aqueous Solutions

et al. 2018

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A synergic approach combining molecular dynamics (MD) simulations and X-ray absorption spectroscopy (XAS) has been used to investigate diluted (0.1 M) aqueous solutions of two lanthanide ions (Ln), namely, La and Dy, with triflate, nitrate, and bis(trifluoromethylsulfonyl)imide (TfN) as counterions. The different complexing ability of the three anions has been highlighted by the analysis of the MD simulations: TfN does not form inner-sphere complexes, while a small amount of triflate coordinates both the La and Dy cations in their first solvation shell. On the other hand, the nitrate ion is almost absent in the La first coordination sphere, while forming contact ion pairs with Dy. Both lanthanide ions are found to preferentially interact with the water molecules, and the total number of oxygen atoms coordinating the Ln cations in their first solvation sphere is the same in all of the solutions, regardless of whether they belong to water molecules or to the counterion. The presence of counterions in the cation first or second shell changes neither the first shell distance nor the symmetry of the hydration complex formed in solution. The MD results have been confirmed by comparison with the Ln K-edge XAS experimental data, and the quantitative analysis of the extended X-ray absorption fine structure (EXAFS) spectra of the three salt solutions has provided a definite proof of the accuracy of the force field employed in the simulations and of the MD structural result. The anion-water and water-water hydrogen bond lifetimes have been analyzed highlighting the slow down effect of the triflate, nitrate, and TfN anions on the hydrogen bond dynamics in the Ln first solvation shell, with the effect being stronger in the Dy solutions, due to the higher charge density of the Dy ion as compared to La.

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Section: Resultsmentioning

confidence: 99%

Influence of Counterions on the Hydration Structure of Lanthanide Ions in Dilute Aqueous Solutions

et al. 2018

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“…In particular, at comparable sizes, anions induce a more pronounced perturbation of their hydration shells compared to cations, because they are hydrogen-bond acceptors. 17,50,113,268,282,294,[296][297][298][299][300][301][302] The same applies to small or/and multivalent ions, because they generate a stronger electric field at their surface. This more important perturbation may require the inclusion of the second hydration shell into the QM region.…”

Section: Discussionmentioning

confidence: 96%

“…In this respect, it is interesting to note that three recent approaches for improving the description of ion-water interactions at the MM level rely in effect on a weakening of the ion-solvent Coulombic interactions. These are: the induction-type 66,67,104,107,[278][279][280][281]284 force fields, where CT effects are included explicitly, the molecular dynamics in electric continuum (MDEC) approach, [285][286][287] where the ion charge is effectively scaled 75,[77][78][79]288 by a factor of about 0.7-0.9 (in line with QM results 282 ), and the multisite ion description, [289][290][291][292][293][294][295] where the ion charge is redistributed over virtual off-center sites within the ion. The observation made here that the features of the QM/MM RDFs can be reproduced more accurately with a MM model when reducing the nominal charge of the ion to +0.75 e is perfectly in line with these considerations.…”

Section: Discussionmentioning

confidence: 99%

Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration

Hofer

Hünenberger

2018

The Journal of Chemical Physics

104

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The absolute intrinsic hydration free energy G • H + ,wat of the proton, the surface electric potential jump χ • wat upon entering bulk water, and the absolute redox potential V • H + ,wat of the reference hydrogen electrode are cornerstone quantities for formulating single-ion thermodynamics on absolute scales. They can be easily calculated from each other but remain fundamentally elusive, i.e., they cannot be determined experimentally without invoking some extra-thermodynamic assumption (ETA). The Born model provides a natural framework to formulate such an assumption (Born ETA), as it automatically factors out the contribution of crossing the water surface from the hydration free energy. However, this model describes the short-range solvation inaccurately and relies on the choice of arbitrary ion-size parameters. In the present study, both shortcomings are alleviated by performing first-principle calculations of the hydration free energies of the sodium (Na + ) and potassium (K + ) ions. The calculations rely on thermodynamic integration based on quantum-mechanical molecular-mechanical (QM/MM) molecular dynamics (MD) simulations involving the ion and 2000 water molecules. The ion and its first hydration shell are described using a correlated ab initio method, namely resolution-of-identity second-order Møller-Plesset perturbation (RIMP2). The next hydration shells are described using the extended simple point charge water model (SPC/E). The hydration free energy is first calculated at the MM level and subsequently increased by a quantization term accounting for the transformation to a QM/MM description. It is also corrected for finite-size, approximate-electrostatics, and potentialsummation errors, as well as standard-state definition. These computationally intensive simulations provide accurate first-principle estimates for G • H + ,wat , χ • wat , and V • H + ,wat , reported with statistical errors based on a confidence interval of 99%. The values obtained from the independent Na + and K + simulations are in excellent agreement. In particular, the difference between the two hydration free energies, which is not an elusive quantity, is 73.9 ± 5.4 kJ mol 1 (K + minus Na + ), to be compared with the experimental value of 71.7 ± 2.8 kJ mol 1 . The calculated values of G • H + ,wat , χ • wat , and V • H + ,wat ( 1096.7 ± 6.1 kJ mol 1 , 0.10 ± 0.10 V, and 4.32 ± 0.06 V, respectively, averaging over the two ions) are also in remarkable agreement with the values recommended by Reif and Hünenberger based on a thorough analysis of the experimental literature ( 1100 ± 5 kJ mol 1 , 0.13 ± 0.10 V, and 4.28 ± 0.13 V, respectively). The QM/MM MD simulations are also shown to provide an accurate description of the hydration structure, dynamics, and energetics. Published by AIP Publishing.

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“…And thus for the hydration of the [CaCl 4 ] 2– cluster, 12 water molecules were considered; 15 and 18 water molecules were considered for the [CaCl 5 ] 3– and [CaCl 6 ] 4– clusters, respectively. Recently, Sessa et al showed that the conventional first shell of a halide ion can be divided into a tight first shell and a loose shell . Such characteristics were taken into account for the construction of initiated hydrated structures of Cl – in [CaCl x ] 2– x ( x = 3–6) clusters.…”

Section: Results and Discussionmentioning

confidence: 99%

“…Recently, Sessa et al showed that the conventional first shell of a halide ion can be divided into a tight first shell and a loose shell. 69…”

Section: Dft Calculationsmentioning

confidence: 99%

High-Order Ca(II)–Chloro Complexes in Mixed CaCl₂–LiCl Aqueous Solution: Insights from Density Functional Theory and Molecular Dynamics Simulations

Wang

2016

J. Phys. Chem. A

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In this study, the structural characteristics of high-coordinated Ca-Cl complexes present in mixed CaCl2-LiCl aqueous solution were investigated using density functional theory (DFT) and molecular dynamics (MD) simulations. The DFT results show that [CaClx](2-x) (x = 4-6) clusters are quite unstable in the gas phase, but these clusters become metastable when hydration is considered. The MD simulations show that high-coordinated Ca-chloro complexes are possible transient species that exist for up to nanoseconds in concentrated (11.10 mol·kg(-1)) Cl(-) solution at 273 and 298 K. As the temperature increases to 423 K, these high-coordinated structures tend to disassociate and convert into smaller clusters and single free ions. The presence of high-order Ca-Cl species in concentrated LiCl solution can be attributed to their enhanced hydration shell and the inadequate hydration of ions. The probability of the [CaClx](2-x)aq (x = 4-6) species being present in concentrated LiCl solution decreases greatly with increasing temperature, which also indicates that the formation of the high-coordinated Ca-Cl structure is related to its hydration characteristics.

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Hidden Hydration Structure of Halide Ions: an Insight into the Importance of Lone Pairs

Cited by 28 publications

References 49 publications

Influence of Counterions on the Hydration Structure of Lanthanide Ions in Dilute Aqueous Solutions

Influence of Counterions on the Hydration Structure of Lanthanide Ions in Dilute Aqueous Solutions

Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration

High-Order Ca(II)–Chloro Complexes in Mixed CaCl₂–LiCl Aqueous Solution: Insights from Density Functional Theory and Molecular Dynamics Simulations

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Hidden Hydration Structure of Halide Ions: an Insight into the Importance of Lone Pairs

Cited by 28 publications

References 49 publications

Influence of Counterions on the Hydration Structure of Lanthanide Ions in Dilute Aqueous Solutions

Influence of Counterions on the Hydration Structure of Lanthanide Ions in Dilute Aqueous Solutions

Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration

High-Order Ca(II)–Chloro Complexes in Mixed CaCl2–LiCl Aqueous Solution: Insights from Density Functional Theory and Molecular Dynamics Simulations

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Product

Resources

About

High-Order Ca(II)–Chloro Complexes in Mixed CaCl₂–LiCl Aqueous Solution: Insights from Density Functional Theory and Molecular Dynamics Simulations