HYDRATION OF LITHIUM ION IN AQUEOUS-SOLUTION

Raman spectra of aqueous lithium salt solutions (LiCl, LiBr, and LiClO 4) were measured from saturation concentrations to more dilute solutio ns at room temperature. In the saturated LiCl and LiBr solutions a pol arized band at 380 and 335 cm(-1), respectively, was detected. This ba nd was assigned to a symmetric vibrational mode from an inner sphere c omplex LiCl/Br(OH2)(n)(+) where n is probably three. In more dilute aq ueous LiCl and LiBr solutions the high frequency component disappeared , and a new polarized band at 255 cm(-1) (FWHH 60 cm(-1)) was observed and assigned to the Li-O symmetric stretching motion of Li-(OH2)(4)(). This is the first definitive report of the symmetric stretching mot ion of an univalent cation. Ab initio geometry optimizations and frequ ency calculations at the 3-21G and 6-31G level were performed on the tetraaquolithium species and support our assignment.