Effects of metal ion on the water structure studied by the Raman O-H stretching spectrum

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+, Mg2+ and Al3+, and between Ca2+ and Mn2+ and Al3+ and Fe3+. 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, MgCl2, AlCl3 and FeCl3 with concentrations of 0 to similar to 1 mol/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 (C) 2009 John Wiley & Sons, Ltd.