Correlation of the Raman ν₁ bands of aquated divalent metal ions with the cation–hydrated water distance

The frequencies of the symmetric stretching ν 1 Raman bands have been measured for aquated Be 2+ , Mg 2+ , Ca 2+ , Mn 2+ , Fe 2+ , Ni 2+ , Zn 2+ , Cd 2+ , Hg 2+ and Pb 2+ ions in aqueous solutions. There is a linear relationship between the frequency of the band and 1/r MO , where r MO is the distance between a metal cation and its hydrated water molecules. It is concluded that the electrostatic theory for ionic hydration can explain most of the hydrations of divalent metal ions in aqueous electrolyte solutions.