A combined experimental and theoretical study on the structures, dynamics and interactions of BMIMTfO and BMIMTFSI binary ionic liquid mixtures

The study of ionic liquid mixtures has garnered growing attention due to its importance. However, our current understanding of molecular interactions in ionic liquid mixtures remains incomplete, necessitating further research to expand the foundational knowledge in this field. In this work, a comprehensive approach incorporating theoretical calculations and diverse experimental techniques was utilized to research the structures, dynamics, and interactions of 1-butyl-3-methylimidazolium trifluoromethansulfonate (BMIMTfO) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (BMIMTFSI) mixtures. The obtained conclusions are as follows: (1) The primary interaction sites for [BMIM](+), [TfO](-) and [TFSI](-) were identified as the C2H, O atoms of SO3 and O atoms of SO, respectively. (2) With the addition of BMIMTFSI, the hydrogen bonding interactions associated with imidazolium CH are weakened, while those associated with alkyl CH and SO are strengthened. Additionally, there is an increased propensity for aggregation between the two anions ([TfO](-), [TFSI](-)) and [BMIM](+). (3) The interactions between [BMIM](+) and [TfO](-) are stronger compared to those between [BMIM](+) and [TFSI](-), and the self-diffusion coefficient followed the order of [BMIM](+) > [TFSI](-) > [TfO](-). (4) The 2[BMIM](+)[TfO](-), 2[BMIM](+)[TFSI](-)-[TfO](-), 2[BMIM](+)[TFSI](-) and 2[BMIM](+)[TfO](-)-[TFSI](-) complexes were assigned using excess spectroscopy and quantum chemical calculations.