On the characterization of some [bmim][X]/co-solvent binary mixtures: a multidisciplinary approach by using kinetic, spectrophotometric and conductometric investigations

In order to study the intrinsic characteristics and to evaluate the structural variations determined by the addition of a co-solvent to 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) we examined the behaviour of some probes in [bmim][BF4]/co-solvent binary mixtures. The rate constants of the piperidino-catalyzed rearrangement of the Z-phenylhydrazone of the 3-benzoyl-5-phenyl-1,2,4-oxadiazole into the relevant 4-benzoylamino-2,5-diphenyl-1,2,3-triazole as well as the spectrometric properties of pyrene and Nile Red were evaluated. With the same purpose also 1H NMR and conductivity measurements were carried out. By comparison the behaviour of 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonylimide)/1,4-dioxane mixtures has been analyzed. The whole of data confirms the presence of weak interactions that determine a partially preorganized structure for [bmim][X]. This is perturbed at some degrees by quantity and nature of guest molecules. For example conductivity measurements support the idea that different charged aggregates are present in the [bmim][X]/co-solvent binary mixtures.