Structure and Dynamics of Hydrated Ions in a Water-Immiscible Organic Solvent

The structure and dynamics of hydrated alkali and halide ions in bulk 1,2-dichloroethane (DCE) are studied using molecular dynamics computer simulations. The number of water molecules in the ions' hydration shell and their orientational distribution, hydration water residence time, and ion diffusion constant are calculated and compared with the same quantities in bulk water. As the ion size increases, the average hydration number in DCE decreases, which is the opposite trend found in bulk water. The water molecules in the first hydration shell of the ion in bulk DCE are more tightly held to the ion, with a longer residence time than in bulk water. The hydrated ions in DCE are more mobile than in bulk water, and their mobility is much less sensitive to the ion size compared with the size dependence in bulk water.