Intermolecular interactions in mixtures of 1-n-butyl-3-methylimidazolium acetate and water: Insights from IR, Raman, NMR spectroscopy and quantum chemistry calculations

The behavior of the obtained spectroscopic data is consistent with the physical picture that when water is added to BmimAc, the interactions between cation-anion are weakened in favor of those between water and anion. The clear spectral signature is associated with the strong blue/red shift of the stretching and bending modes of the C(2)-H, respectively. Consistently with this spectral behavior, the corresponding 1H and 13C chemical shifts decrease when adding water to BmimAc. The strengthening of the water-anion interactions is also traced back to both the blue shift of the νs(COO−) at around 1380 cm− 1 and ν(C-C) of acetate at around 920 cm− 1 as well as the blue shift of the δ(COO−) at around 637 cm− 1 and ω(COO−) at 615 cm− 1. The 1H, 13C and 17O chemical shifts of COO− are consistent with the corresponding spectral behavior.