Study on the interactions between [BMIM][SCN] and naphtalene/dibenzothiophene: A theory-experiment comparison

Abstract

Interactions between the ionic liquid (IL), 1-butyl-3-methylimidazolium thiocyanate [BMIM][SCN], and two polycyclic aromatic hydrocarbons (PAHs), naphthalene (NPT) and dibenzothiophene (DBT), were studied, from the theoretical point of view, using Atoms In Molecules (AIM) and Non Covalent Interactions (NCI) methodologies through density functional theory, at the M06-2X/6-311++G** level of calculation. In addition, 1H Nuclear Magnetic Resonance spectroscopy was carried out. Theoretical and experimental results show that the complexes IL-PAHs are stabilized mainly by interactions of the cation-π type, hydrogen bonds, as well as CH-π. Also, the spectroscopic data showed that the interaction was stronger in the case of the [BMIM][SCN]-DBT complex with respect to the [BMIM][SCN]-NPT complex, since DBT has a higher dipolar moment than NPT, this is due to the capacity of the sulfur atom to form extra hydrogen bonding. This result is also in good agreement with the calculated thermodynamics. The [BMIM][SCN] capacity to break the π-π stacking between NPT-NPT and DBT-DBT molecules was also explored in gas phase. Theoretical results showed that the formation of the complex between the ionic liquid and dibenzothiophene was exothermic and slightly spontaneous, whereas the opposite was found for the analogous process with NPT. Therefore, [BMIM][SCN] would be a better solvent for DBT.