Effects of metal ion on the water structure studied by the Raman OH stretching spectrum

Abstract Raman spectra in the OH stretching region of aqueous salt solutions were measured and compared, and the effects of metal ions on water structure deduced. The effects of alkali ions, alkaline ions or the first‐row transition metals on water structure were found to be similar. Differences of metal ionic effects on water structure exist among Na + , Mg 2+ and Al 3+ , and between Ca 2+ and Mn 2+ and Al 3+ and Fe 3+ . The factors that influence the metal ionic effects on the water structure are the ionic charge, the outmost electronic structure and ionic size, the ionic charge being the most important. With a five‐component Gaussian deconvolution of the Raman spectra of the aqueous solutions of NaCl, MgCl 2 , AlCl 3 and FeCl 3 with concentrations of 0 to ∼1mol/l, the ionic effects were found to be similar on the bands at 3233, 3393, 3511 and 3628 cm −1 , but different on the band at 3051 cm −1 . With increasing polarization of the metal ion, the band at 3051 cm −1 , due to strong hydrogen bonding, increases. Copyright © 2009 John Wiley & Sons, Ltd.