Characterization of the F−-water and Cl−-water hydrogen bonds in aqueous solution: From “interior” (I) to “surface” (S) states

Abstract

The ONIOM-XS MD technique has been applied to characterize the F−-water and Cl−-water hydrogen bonds (HBs) in aqueous solution. The QM region, which includes the anion and its surrounding water molecules, was treated by the HF method using the D95+* and D95** basis sets for the anions and water, respectively, while the rest, i.e., the MM region, was described by MM potentials. The ONIOM-XS MD results reveal a clear “structure-making” ability of F− in ordering its surrounding waters to form its specific linearly F−-water HB complexes. Comparing to F−, the structure of the Cl− hydrates is more flexible, showing a combination between the linear and bridging Cl−-water HB formations as well as the HB interactions among the first-shell water molecules. The observed differences in the structure and dynamics of the hydrated F− and Cl− complexes clearly visualize a transition from “interior” (I) to “surface” (S) states.