Strong Similarities in the Local Hydration Environments of the Bromide Ion and the Cl-·CCl3• Ion−Radical Complex: Factors Contributing to Intramolecular Distortions in the Primary Hydration Shell

Abstract

We report the infrared photofragmentation spectra of the Cl-·CCl3·nH2O, n = 1−3 complexes and compare the observed pattern of OH stretching vibrations with those displayed by the X-·nH2O, [X = Cl, Br] clusters. The predissociation spectra reveal hydrogen bonded networks in the di- and trihydrate clusters. Addition of the CCl3• radical to the Cl-·nH2O complexes causes a significant blue shift in the OH stretching vibrations involving the hydrogen atoms bound to the ion. As a result, the Cl-·CCl3·nH2O spectra appear remarkably similar to those observed previously for the bromide hydrates. We trace this effect to partial charge delocalization onto the CCl3• radical through an analysis of the electronic structure carried out with density functional calculations. Two important factors contributing to the ion-bound OH stretch frequencies are the radius, (ri), and excess charge, (qi), associated with the halide. The red shifts displayed by the water molecule in a number of halide−water complexes are found to be ...