FTIR study of ion solvation and ion-pair formation in alkaline and alkaline earth metal salt solutions in acetonitrile

Abstract

The IR spectra of alkaline and alkaline earth metal perchlorate and of lithium bromide solutions in acetonitrile, obtained with the help of FTIR measurements in the region of the C-N stretching mode of the solvent, reveal bands produced by acetonitrile molecules in the solvation shells and bands of ClO 4 − ions in contact and solvent separated ion pairs. The shift and the attenuation of the C-N stretching band of acetonitrile at 2254 cm−1 is used for the calculation of cation solvation numbers for Li+(4), Na+(4), Mg2+(6), Ca2+(6), and Ba2+(6). No solvation is assumed for the contact ion pairs of LiClO4, LiBr, NaClO4, Mg(ClO4)2, Ca(ClO4)2, and Ba(ClO4)2. The association constants of the symmetrical electrolytes are compared to those obtained from other methods.