Solvation structures of lithium halides in methanol-water mixtures

The potentials of mean force (PMFs) for the ion pairs, Li+-Cl, Li+-Br and Li+-I have been calculated in five methanol-water compositions. The results obtained are verified by trailing the trajectories and calculating the ion pair distance residence times. Local structures around the ions are studied using the radial distribution functions, density profiles, orientational correlation functions, running coordination numbers and excess coordination numbers. The major change in PMF is observed as the methanol mole fraction (chi(methanol)) is changed from 1.0 to 0.75. The stable contact ion pair occurring for chi(methanol) = 1.0 becomes unstable at and below chi(methanol) = 0.75. The preferential solvation data show that the halide ions are always preferentially solvated by water molecules. Although the lithium ion is preferentially solvated by methanol molecules, there is significant affinity towards water molecules as well. (C) 2014 Elsevier B.V. All rights reserved.