Preferential Solvation of Mg2+ in Ethanol-Water Mixtures Probed by Intermolecular Coulombic Decay and Molecular Dynamics Simulations.

The microsolvation of Mg2+ ions in ethanol-water mixtures was investigated using intermolecular Coulombic decay (ICD) after Mg 1s ionization, a nonlocal relaxation process involving the ejection of valence electrons from molecules in the first solvation shell. As the solvent composition shifts from pure water to pure ethanol, the ICD spectral shape evolves, and its total intensity decreases by 20% relative to the local Mg KLL Auger decays. Spectral analysis reveals that Mg2+ ions are preferentially solvated by water; a substantial contribution from ethanol is observed only at high ethanol concentrations. Molecular dynamics simulations corroborate the experimental results, and together they provide quantitative understanding for the changes in solvation-shell composition, revealing a substantial enrichment of water in the solvation shell relative to the bulk solvent composition.