FTIR and quantum chemical study of LiBr solvation in acetonitrile solutions

• Combined MP2 + SMD and FTIR investigations of ionic species in LiBr/acetonitrile solutions.
• The IR spectra for all stable ionic species solvated by acetonitrile molecules were calculated.
• All stable complexes are spectroscopically discernible.
• The far-infrared region of the IR spectrum is very sensitive with respect to the complex geometry.
• The composition and geometry of predominant complexes were established.

FTIR spectroscopy and quantum chemical calculations at the RTF + MP2/6-311G** level of theory with solvation model density (SMD) corrections were used to study ion solvation and association in LiBr/acetonitrile solutions. The aim of this study was to establish the composition and geometry of the predominant ionic species solvated by acetonitrile molecules and to analyse their spectroscopic signatures. The results obtained make it possible to propose an equilibrium between Li+Br−(CH3CN)3, Li+(CH3CN)4, and anionic Br−(CH3CN)n complexes with an undetermined n value and bent coordination of the solvent molecules. The calculated wavenumbers and the geometric parameters of the solvated ionic species were found to be in excellent agreement with the experimental data.