Solvation of Co2+ ion in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid: A molecular dynamics and X-ray absorption study
| Autor: | Andrea Melchior, Matteo Busato, Andrea Lapi, Marilena Tolazzi, Paola D'Angelo |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
Materials science
Absorption spectroscopy Enthalpy Solvation 02 engineering and technology 010402 general chemistry Cobalt EXAFS Ionic liquids Molecular dynamics simulations XANES 01 natural sciences chemistry.chemical_compound Materials Chemistry Physical and Theoretical Chemistry Spectroscopy Extended X-ray absorption fine structure 021001 nanoscience & nanotechnology Condensed Matter Physics C4mim Atomic and Molecular Physics and Optics 0104 chemical sciences Electronic Optical and Magnetic Materials chemistry Ionic liquid Outer sphere electron transfer Physical chemistry Absorption (chemistry) 0210 nano-technology |
| Popis: | The solvation of the Co2+ ion in the [C4mim][Tf2N] (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) room temperature ionic liquid (RTIL) has been studied from both a structural and thermodynamic point of view. Co K-edge X-ray absorption spectroscopy (XAS) data have been collected on a 0.1 M Co(Tf2N)2 solution in [C4mim][Tf2N] as well as on the metallic salt and classical MD simulations have been performed to obtain both structural and thermodynamic data. The analysis of the extended X-ray absorption fine structure (EXAFS) region of the spectrum of the liquid sample has been carried out with the aid of MD simulations showing that the [Co(Tf2N)6]4− complex is formed in solution. A different coordination is present in the solid compound, where Co2+ is coordinated by two bidentate and two monodentate anions to form a [Co(Tf2N)4]2− unit. Thermodynamic data obtained from free energy calculations provide a strongly negative solvation free energy (ΔGsolv) which is qualitatively similar to that previously found for the Zn2+ ion. Free energy calculations carried out at variable temperature provided negative values for both ΔΗsolv and ΔSsolv. Thermodynamic parameters for the water→[C4mim][Tf2N] ion transfer (ΔGtrans, ΔΗtrans and ΔStrans) have been also obtained. The positive ΔGtrans shows that Co2+ is preferentially solvated by water, in agreement with the spectral changes in the visible region occurring when water is added to a Co2+ solution in dry [C4mim][Tf2N] even at low H2O/metal ratios. At higher water concentrations (up to the saturation limit), the spectrum is compatible with the presence of the [Co(H2O)6]2+ species. Interestingly, the positive ΔGtrans results from a compensation between ΔΗtrans and ΔStrans, which are both negative. However, the ligand exchange energy calculated for the CoL6 complexes (L = [Tf2N]− and H2O) indicates that [Tf2N]− is a much weaker ligand than water. This evidence suggests that the energetic contributions to the overall solvation enthalpy due to outer sphere effects are markedly different in water and [C4mim][Tf2N], so that the final ΔHtrans results to be negative. |
| Databáze: | OpenAIRE |
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