Infrared spectroscopic study of interionic hydrogen bonds in triethylammonium salts

Abstract

The frequencies and integrated intensities of the stretching vibration bands ν_N⁺H were measured in the i.r. spectra of the triethylammonium salts Et₃N⁺H…Y^–(Y^–= PF^–₆, BF^–₄, ClO^–₄, FSO^–₃ and ClSO^–₃) in [²H₃]acetonitrile, [²H₁]chloroform, [²H₆]acetone, nitrobenzene, [²H₆]dimethylsulphoxide and [²H₅]pyridine solvents. The complex structure of the ν_N⁺H band observed was in all cases shown to be independent of the type of the solvent (excluding dimethylsulphoxide and pyridine), the temperature and the concentration, and to have been caused by Fermi resonance perturbations of ν_N⁺H↔ 2δ_N⁺H and ν_N⁺H↔δ_N⁺H+ν_CN. The parameters of these interactions (Fermi coupling constant W) were evaluated. The values of the frequency and intensity of the stretching band ν_N⁺H were obtained for a “free” triethylammonium cation. The energies of the H bonds of N⁺—H…Y^– in the above triethylammonium salts were estimated from the spectral parameters.