TY - JOUR
T1 - Cooperativity and ion pairing in magnesium sulfate aqueous solutions from the dilute regime to the solubility limit
AU - Sebastiani, Federico
AU - Verde, Ana Vila
AU - Heyden, Matthias
AU - Schwaab, Gerhard
AU - Havenith, Martina
N1 - Funding Information:
We acknowledge Prof. H. Weingärtner for scientific support and helpful discussions, and Drs F. Böhm and L. Grimmelsmann for their help with preliminary measurements. Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) im Rahmen der Exzellenzstrategie des Bundes und der Länder ‘‘EXC 2033’’ Projektnummer 390677874 RESOLV (this work is supported by the Cluster of Excellence RESOLV (EXC2033, project 390677874) funded by the Deutsche Forschungsgemeinschaft).
Publisher Copyright:
© the Owner Societies 2020.
PY - 2020/6/7
Y1 - 2020/6/7
N2 - We report a terahertz absorption spectroscopy study of MgSO4aqueous solutions in the concentration range 0.1 mol dm−3to 2.4 mol dm−3. Accompanying classical MD simulations were carried out that use a polarizable force field parameterized to reproduce the solution thermodynamics. Contrary to prior reports, we find no evidence of contact ion pairs, even close to the solubility limit. Only solvent separated and different types of solvent shared ion pairs are found, being abundant even at the lowest concentration investigated here. The structure of the solution is concentration-dependent: the number of both types of ion pairs grows with increasing salt concentration. The combined theoretical and experimental analysis of the spectra in the frequency region 50-640 cm−1suggests that the dynamics of water directly between two ions in solvent shared configuration is very strongly perturbed,viaa cooperative, supra-additive, effect arising from the two ions. At high concentrations, the results support a scenario, where the perturbations in the water dynamics extend up to the third hydration layerviaa cooperative, but additive, effect involving multiple ions. The SO42−and its hydration shell are much more strongly perturbed by the presence of the counterions than the first hydration shell of Mg2+. It is further shown that our simulations and observations are in agreement with thermodynamic properties of aqueous MgSO4solutions derived by other methods.
AB - We report a terahertz absorption spectroscopy study of MgSO4aqueous solutions in the concentration range 0.1 mol dm−3to 2.4 mol dm−3. Accompanying classical MD simulations were carried out that use a polarizable force field parameterized to reproduce the solution thermodynamics. Contrary to prior reports, we find no evidence of contact ion pairs, even close to the solubility limit. Only solvent separated and different types of solvent shared ion pairs are found, being abundant even at the lowest concentration investigated here. The structure of the solution is concentration-dependent: the number of both types of ion pairs grows with increasing salt concentration. The combined theoretical and experimental analysis of the spectra in the frequency region 50-640 cm−1suggests that the dynamics of water directly between two ions in solvent shared configuration is very strongly perturbed,viaa cooperative, supra-additive, effect arising from the two ions. At high concentrations, the results support a scenario, where the perturbations in the water dynamics extend up to the third hydration layerviaa cooperative, but additive, effect involving multiple ions. The SO42−and its hydration shell are much more strongly perturbed by the presence of the counterions than the first hydration shell of Mg2+. It is further shown that our simulations and observations are in agreement with thermodynamic properties of aqueous MgSO4solutions derived by other methods.
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U2 - 10.1039/c9cp06845g
DO - 10.1039/c9cp06845g
M3 - Article
C2 - 32436497
AN - SCOPUS:85085960111
SN - 1463-9076
VL - 22
SP - 12140
EP - 12153
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
IS - 21
ER -