IR spectroscopic and quantum-chemical investigation of perchlorate anion solvation in acetonitrile

The solvation of anions in solutions of tetrabutylammonium perchlorates in acetonitrile is studied by means of quantum-chemical calculations and Fourier-transform infrared spectroscopy. It is shown that perchlorate-anions form stable solvate complexes with acetonitrile molecules due to ion-dipole interactions between atoms of oxygen in the composition of ClO4− anion and hydrogen atoms of methyl groups of solvent molecules. It is established that the energy of formation of anionic solvate complexes ClO4−(CH3CN)n (n = 1–4) is comparable in value that of cation solvate complexes Li+(CH3CN)n (n = 1–4) and is about one third of the latter. This requires us to consider the solvation of perchlorate anions along with the solvation of metal cations in acetonitrile. Spectroscopic signs of perchlorate anion solvation by acetonitrile molecules are analyzed.