Association structures of ionic liquidDMSO mixtures studied by high-pressure infrared spectroscopy

摘要

Using high-pressure infrared methods, we have investigated close interactions of charge-enhanced C-H-O type in ionic liquiddimethyl sulfoxide (DMSO) mixtures. The solvation and association of the 1-butyl-3- methylimidazolium tetrafluoroborate (BMI + BF 4 -) and 1-butyl-2,3- dimethylimidazolium tetrafluoroborate (BMM + BF 4 -) in DMSO-d_6 were examined by analysis of C-H spectral features. Based on our concentration- dependent results, the imidazolium C-H groups are more sensitive sites for C-H-O than the alkyl C-H groups and the dominant imidazolium C-H species in dilute ionic liquidDMSO-d_6 should be assigned to the isolated (or dissociated) structures. As the dilute mixtures were compressed by high pressures, the loss in intensity of the bands attributed to the isolated structures was observed. In other words, high pressure can be used to perturb the association-dissociation equilibrium in the polar region. This result is remarkably different from what is revealed for the imidazolium C-H in the BMM + BF 4 - D_2O mixtures. DFT-calculations are in agreement with our experimental results indicating that C4-H-O and C5-H-O interactions seem to play non-negligible roles for BMM + BF 4 - DMSO mixtures.