Vibrational spectroscopic characterization of stable solvates in the LiClO4/formamide:acetonitrile system

Raman and infrared (IR) experiments of extremely high concentrated solutions (1.0–5.0 M) of lithium perchlorate in equimolar formamide (FA) and acetonitrile (ACN) mixture were carried out. Raman quantitative analyses performed in the CO and CN bands of FA and ACN, respectively, the appearance of a new IR band in the N–H stretching region and the presence of the band at 939 cm−1 were interpreted in terms of a solvent separated ion pairs model. In salt concentrations higher than 3.0 M, a weak band at 945 cm−1 (contact ion pairs) can also be seen. Indeed, the mixture of solvents with considerable differences in the acid-base characters allows to prepare electrolytic solutions where the contact ion pairs formation is low. A coordination number of 4 for the lithium cation is suggested and this value is in full agreement with other authors. Fundamental aspects and the importance of the present system for the development of new lithium-based rechargeable batteries are also discussed.