Effects of the Interaction between Ionic Liquids and Redox Couples on Their Reaction Entropies

The temperature dependence of the potential, d E /d T , of some redox couples was determined using an isothermal cell with ferrocenium / ferrocene couple as a calibration redox couple in different ionic liquids, BMPTFSA, EMITFSA, PP13TFSA, BMPBETA and EMI[BF 4 ] (BMP + = 1-butyl-1-methypyrrolidinium, EMI + = 1-ethyl-3-methylimidazolium, PP13 + = 1-methyl-1-propylpiperidinium, TFSA − = bis(trifluoromethylsulfonyl)amide and BETA − = bis(perfluoroethylsulfonyl)amide). The reaction entropies of the redox couples, Δ rc S °, were calculated from the d E /d T values. It is suggested that the coulombic interaction between the redox couples and the ions with the opposite sign of charge to those of the redox couples is a dominant factor determining the Δ rc S ° value and that the absolute Δ rc S ° value for the redox couple increases with an increase in the charge density of the ions with the opposite charge to the redox couple. However, the Δ rc S ° values are considered to be affected not only by the charge density of the ions but also by the polarization and/or steric shape of the ions.