Extensive measurements of the intervalence-transfer absorption band energy of the (NH3)5RuII  -4,4'bpy-RuIII  (NH3)55+ Mixed-Valence dimer in both H2O and D2O have been carried out in the presence of a selection of simple alkali-metal halide and other added salts. In contrast with previous investigations of salt effects on this system, we observe distinct red shifts in the optical energy gap with the majority of salts investigated as well as with the neutral molecular solutes studied. In the halide series, for example, added fluoride causes a non-linear but smoothly-varying blue shift in the band energy whereas chloride, bromide and iodide cause progressively stronger red shifts (with no resolvable-dependence on the identity of the cation). These and related results call for a reconsideration of the nature of the outer-sphere ET reorganizational barrier in such strongly-hydrated systems. We will offer interpretations based on the known water-structure altering properties of the various anions involved as well as an analysis showing a probable role for both anionic and neutral solute perturbations of the electronic polarizability of the medium surrounding the chromophore.

Novel ion-pairing and ion-atmosphere effects on the intervalence-transfer band energy of the symmetrical (NH3)5RuII -4,4'bpy-RuIII (NH3)55+ mixed-valence dimer in water and D2O: Possible roles for anion-induced hydration-sphere structural modifications as well as changes in the effective medium electronic polarizability induced by added anions and neutral solutes

248th National Meeting (2014)

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