A Metallacage Encapsulating Chloride as a Probe for a Solvation Scale in Ionic Liquids

With the purpose of assessing the reactivity of chloride ions dissolved in ionic liquids (ILs), a relative scale for the solvation of chloride is given for a series of ILs based on the bis(trifluoromethane)sulfonimide ([Tf2N]) anion and different cations, 1-butyl-3-methylimidazolium ([bmim]), 1-butyl-2,3-dimethylimidazolium ([bdmim]), 1-butyl-1-methylpyrrolidinium ([bmpy]), 1-butylpyridinium ([bpy]), 1-pentyl-1,1,1-triethylammonium ([C5e3am]), and 1-(2-hydroxy)ethyl-3-methylimidazolium ([mimeOH]). Insights into the solvation of chloride are achieved by the thermodynamic study of the reaction of dissociation of a chloride-templated nickel(II) metallacage performed at various temperatures by UV-visible spectroscopy in each IL. The order of chloride solvation [C5e3am][Tf2N] < [bmpy][Tf2N] < [bmim][Tf2N] ≤ [bdmim][Tf2N] < [bpy][Tf2N] << [mimeOH][Tf2N] was ascertained from the reaction enthalpies determined in the different ILs. The reaction entropies display a concentration-dependent behavior, which has highlighted a correlated motion of the ions in these ILs.