Communication: solute anisotropy effects in hydrated anion and neutral clusters

Specific ion effects in solvation processes are often rationalized in terms of spherically symmetric models involving an ion's size, charge, and polarizability. The effects of permanent charge anisotropy, related to the polyatomic nature of complex solutes, are expected to play a role in solvation but the extent of their importance remains unexplored. In this work, we provide compelling experimental and theoretical evidence that the anisotropic nature of complex polyoxyanion solutes can have a critical influence on the solvation process. Combined photoelectron spectroscopy and theoretical modeling results show that the electron binding energy of IO(3) (-)(H(2)O)(n) (n = 0-12) clusters is characterized by an anomalous drop at n = 10. Such behavior is unprecedented for rigid solute molecules and is related to the anisotropy of the neutral iodate radical that displays a strong selectivity to solvent configurations generated by the charged anion complex. These results highlight the significance of solute anisotropy and its potential impact on ion specificity and selectivity in aqueous environments.