FTIR and Raman study of lithium salts solutions in diethylsulfoxyde.

The curve fitting procedure has been performed for both IR and Raman spectra in SO and CH stretching regions for lithium salts solutions in diethylsulfoxide (DESO). The broad S=O stretching bands of DESO (1100 - 950 cm"1) show seven or eight components on band deconvolution. On th\ue8 basis of th\ue8 previous studies [1, 2] on solution DESO in aqueous and non-aqueous solutions, th\ue8 various components are assigned to free and associated species of DESO. The low-frequency component observed in solutions of lithium chloride in DESO at 1007 cm"1 is assigned to cation-molecular complexes. Lf-DESO associate is formed through th\ue8 interaction between Li* and S=O group of DESO, that leads to th\ue8 increase of SO stretching frequency. The spectral changes of th\ue8 SO stretching bands indicate that interaction between th\ue8 Li* ion and diethylsulfoxide breaks partially down th\ue8 self-association of th\ue8 solvent. In both IR and Raman spectra th\ue8 curve fitting procedure in CH stretching region (3000-2700 cm"1) gives five components, caused by antisymmetric and symmetric stretching vibrations of CH3 and CH2 groups of DESO. It is observed that both CH3 and CH2 stretching bands are shifted to th\ue8 high-frequency side in solutions of lithium nitrate and perchlorate in DESO, and to low-frequency side in solutions of lithium chloride in com-parison with their position in pure DESO. The increase of th\ue8 salt concentration in th\ue8 solution not only results in th\ue8 formation of Li*-DESO associates, but also makes th\ue8 elec-tronic nebula of th\ue8 C-H bond increase by way of th\ue8 induction effect transferred along th\ue8 molecular chain. This mechanism can explain th\ue8 changes in th\ue8 frequency of th\ue8 CH stretching modes in case of lithium nitrate and perchlorate solutions. The low-frequency shift in solutions of lithium chloride indicates th\ue8 existence of interactions between th\ue8 CH2 group of DESO and th\ue8 chloride anion. The curve fitting procedure performed for th\ue8 out-of-plane bending of NO}" anion (840-820 cm"1) in IR spectra, and for th\ue8 totally symmetric stretching vibration of C1O4" anion (950-920 cm"1) in Raman spectra has shown th\ue8 coexistence of free ions and contaci ion pairs. The comparison of experimental and theoretical calculated frequencies shows that th\ue8 coordination of C1O4" in th\ue8 ion pairs Li*ClO4" is monodentate