Mixed Ionic Liquids: The Case of Pyridinium-Based Fluids

We report in this work a combined experimental and computational study on the molecular level structuring of binary ionic liquid mixtures comprising pyridium cations. The effect of anions on liquid structure was analyzed from the mixing (mixture 1) of [b3mpy][BF4] and [b3mpy]-[N(CN)(2)] ionic liquids, in the full composition range, leading to [b3mpy][BF4](x)[N(CN)(2)](1-x) mixed ionic liquids. The effect of the length of alkylic chains in cations was studied with mixtures (mixture 2) of [b3mpy][BF4] and [o3mpy][BF4] ionic liquids, also studied in the full composition range, leading to [b3mpy](x)[o3mpy](1-x)[BF4] ionic liquids. Fourier transform infrared-attenuated total reflection spectra were recorded and analyzed as a function of anionic and cationic composition for the two studied mixture types. Classical molecular dynamics simulations were also performed for mixtures 1 and 2 as a function of anionic and cationic composition. The reported experimental and computational results show that the properties of the studied mixed systems change in an almost linear way, leading to almost ideal mixtures from the thermodynamic viewpoint, and thus pointing to simple dilution effects of the involved ions controlling the mixture properties.