Hydration of Metal and (CH3)4N+ Ions in Solutions of Mixed Salts

Molecular dynamic simulations of aqueous solutions containing Me₄NCl and an inorganic salt, NaCl, MgCl₂ or CaCl₂, have been performed at room temperature. Flexible models have been employed for the Me₄N⁺-ions and the water molecules. The hydration of the ions has been discussed on the basis of the radial and angular distribution functions. The geometrical arrangement of the water molecules in the coordination shell has been deduced form the distributions of the angles between two vectors connecting the ion and an oxygen and of the angles between three oxygens. The addition of Me₄N⁺ does not influence noticeably the size and structure of the cationic hydration shells, but it affects remarkably their persistence, causing a fast exchange of the water molecules between the shell and the bulk solvent.