PNNL

Abstract

We show, through a combination of density function theory based molecular dynamics simulations (DFTMD) and experimental x-ray absorption fine structure spectroscopy (XAFS) studies, that the iodate ion (IO3-) is a zwitterion in solution. The local region adjoining the I atom is sufficiently electropositive that three hydrating waters are oriented with their O’s atoms directly interacting with the iodine atom at an I-OH2O distance of 2.95 Å. This is the orientation of water hydrating a cation. Further, approximately 2-3 water molecules hydrate each O of IO3 - through a single H atom in an orientation of the water that is expected for an anion at an IOH2O distance of 3.85 Å. We predict that this structure persists, although to a much lesser degree, for BrO3 -, and ClO3 -. This type of local microstructure profoundly affects the behavior of the "anion" at interfaces and how it interacts with other ionic species in solution.