Vibrational Spectroscopic Identification of the [AlCl2]+ Cation in Ether-Containing Liquid Electrolytes

A Raman and IR study of AlCl3-based ethereal solutions is here presented and aims at identifying the [AlCl2]+ cation, which has been so far unambiguously characterized by 27Al NMR spectrometry. To do that, experimental–theoretical vibrational spectroscopy was so employed, and the data are interpreted successfully. As a known amount of water is added to the tetrahydrofuran (THF)-containing electrolyte, a Raman band at 271 cm−1 has its intensity increased along with the most intense band of [AlCl4]−, and such behavior is also seen for a band at 405 cm−1 in the IR spectra. New bands at around 420 and 400 cm−1 are observed in both Raman and IR spectra for the tetraglyme (G4)-based systems. The [AlCl2(THF)4]+ complex, in the cis and trans forms, is present in the cyclic ether, while the cis-[AlCl2(G4)]+ isomer is identified in the acyclic one.