Molecular interactions in methylimidazolium tetrafluoroborate ionic liquid ([Mim][BF4]): Structures, binding energies, topological properties and NMR one- and two bonds spin-spin coupling constants

Molecular interactions in methylimidazolium tetrafluoroborate ionic liquid (Mim⁺]BF₄⁻]) have been investigated using B3LYP, B3PW91 and MP2 methods with a wide range of basis sets. Binding energy, topological properties of electron density, charge transfer, nucleus-independent chemical shift (NICS) and NMR one- and two bonds spin-spin coupling constants were calculated. With five preferential binding sites in the vicinity of the Mim⁺ ring, five ion pairs (A-E) with three intermolecular hydrogen bonds were found on the potential energy surface. The most stable ion pairs are formed via N-H and C-H bonds of Mim⁺ and B-F bonds of BF₄⁻. Ion pairs have electronic binding energies (BEs) in the range of − 335.6 to − 402.9 kJ/mol at MP2/6-311++G(2d,2p) level and − 328.1 to − 383.6 kJ/mol at B3LYP/AUG-cc-pVTZ level. NBO analysis confirms that the charge transfer takes place from BF₄⁻ to Mim⁺. The NICS values reveal the aromaticity of imidazole ring. The results show a correlation between absolute value of ^1hJ(H?F) and electron density at H?F bond critical point.