Coordination and solvation of noble metal ions:: Infrared spectroscopy of Ag+(H2O)n

Vibrational spectra of mass-selected Ag+(H2O)(n) ions are measured by infrared photodissociation spectroscopy and analyzed with the aid of density functional theory calculations. Hydrogen bonding between H2O molecules is found to be absent for cold Ag+(H2O)(3), but detected for Ag+(H2O)(4) through characteristic changes in the position and intensity of OH-stretching transitions. The third H2O coordinates directly to Ag+, but the fourth H2O prefers solvation through hydrogen bonding. The preference of the tri-coordinated form is attributed to the inefficient 5s-4d hybridization in Ag+, in contrast to the efficient 4s-3d hybridization in Cu+. For Ag+(H2O)(4), however, di-coordinated isomers are identified in addition to the tri-coordinated one.