Nature of hydration shells of a polyoxy-anion with a large cationic centre: The case of iodate ion in water

Abstract

The structural nature of the solvation shells of an iodate ion, which is known to be a polyoxy-anion with a large cationic centre, is investigated by means of Born–Oppenheimer molecular dynamics (BOMD) simulations using BLYP and the dispersion corrected BLYP-D3 functionals. The iodate ion is found to have two distinct solvation regions around the positively charged iodine (iodine solvation shell or ISS) and the negatively charged oxygens (oxygen solvation shell or OSS). We have looked at the spatial, orientational, and hydrogen bond distributions of water in the two solvation regions. It is found that the water orientational profile in the ISS is typical of a cation hydration shell. The hydrogen bonded structure of water in the OSS is found to be very similar to that of the bulk water structure. Thus, the iodate ion essentially behaves like a positively charged iodine ion in water as if there is no anionic part. This explains why the cationic character of the iodate ion was prominently seen in earlier studies. The arrangement of water molecules in the two solvation shells and in the intervening regions around the iodate ion is further resolved by looking at structural cross-correlations. The electronic properties of the solvation shells are also looked at by calculating the solute–solvent orbital overlap and dipole moments of the solute and solvation shell water. We have also performed BOMD simulations of iodate ion-water clusters at experimentally relevant conditions. The simulation results are found to be in agreement with experimental results. © 2018 Wiley Periodicals, Inc.