Studies of anion solvation in polar aprotic solvents

Infrared spectra for LiI solutions in acetonitrile (AcN) and dimethyl sulfoxide (DMSO) are presented and analyzed. It is shown that characteristic vector analysis provides an effective tool for determining the effect of the electrolyte on the spectral features. In the case of AcN, the iodide anion interacts with the methyl group of the solvent molecule, which is at the positive end of the molecular dipole. In the case of DMSO, the anion interacts with the sulphur atom in the molecule, which is easily available to a monoatomic anion such as iodide. However, the spectral features of DMSO are complex in the region of the SO stretch so that an unambiguous identification of the anion effects cannot be made without further experimental work with other electrolytes. In the case of AcN, the spectral data are compared with the results of quantum chemical calculations.