Electrode reactions of tris(1,10-phenanthroline)iron complexes, [Fe(phen) 3 ] 3+/2+ , were investigated in some amide-type ionic liquids. The diffusion coefficients of [Fe(phen) 3 ] 2+ and [Fe(phen) 3 ] 3+ were smaller than those of tris(2,2 -bipyridine)iron complexes, [Fe(bpy) 3 ] 2+ and [Fe(bpy) 3 ] 3+ , in each ionic liquid, reflecting the phen complexes are larger than the bpy complexes. The ratio of diffusion coefficient of the trivalent species to that of the divalent one for [Fe(phen) 3 ] 3+/2+ was smaller than that for [Fe(bpy) 3 ] 3+/2+ , indicating the coulombic interaction between the charged species and the ions composing the ionic liquid is dependent on the charge densities of complexes. The rate constants for [Fe(phen) Electrochemical behavior of metal complexes in ionic liquids have been known to depend on the physicochemical properties of the ionic liquids.1-5 Since ionic liquids are composed of only cations and anions without any neutral molecule, the coulombic interaction between a charged species and the ions composing ionic liquids is significant compared with conventional aqueous or organic electrolyte solutions. Diffusion of a species in the conventional solutions is often represented by Stokes-Einstein relation, which is derived simply from the balance between the thermodynamic force based on the activity gradient of the species and the frictional force depending on the size of the species and the viscosity of the solution. However, Stokes-Einstein relation is inaccurate for a charged species even in conventional solutions. For polar solvents, modification of Stokes-Einstein relation has been proposed by considering dielectric friction in addition to the viscous drag.6,7 It has been known that the diffusion of a charged species dissolved in ionic liquids is affected not only by the viscosity of ionic liquids but also by the coulombic interaction between the charged species and the ions composing the ionic liquids, 1,2,4,5 suggesting Stokes-Einstein relation also needs some modification for the charged species diffusing in the ionic liquids. The charge transfer rate of the outer-sphere electron transfer complex is also known to be influenced by the physicochemical properties of the media. 8 The frequency factor of rate constant depends on the solvent dynamics, which is closely related to the viscosity of the medium. The activation Gibbs energy is given by the reorganization energy, which is composed of the inner and outer components. Although the inner component related to the bonds between the center metal and the ligands is insensitive to the medium, the outer component is dependent on the interaction between the complex and the medium. In conventional solutions, the outer component of reorganization energy is mainly determined by the dielectric interaction. However, the contribution of the coulombic interaction to the outer component is expected to be dominant in ionic liquids. Furthermore, the reaction entropy of the redox complexes without the change of their coordi...

Electrode reactions of tris(1,10-phenanthroline)iron complexes, [Fe(phen) 3 ] 3+/2+ , were investigated in some amide-type ionic liquids. The diffusion coefficients of [Fe(phen) 3 ] 2+ and [Fe(phen) 3 ] 3+ were smaller than those of tris(2,2'-bipyridine)iron complexes, [Fe(bpy) 3 ] 2+ and [Fe(bpy) 3 ] 3+ , in each ionic liquid, reflecting the phen complexes are larger than the bpy complexes. The ratio of diffusion coefficient of the trivalent species to the divalent one for [Fe(phen) 3 ] 3+/2+ was smaller than that for [Fe(bpy) 3 ] 3+/2+ , indicating the coulombic interaction between the charged species and the ions composing the ionic liquid is dependent on the charge densities of complexes. The rate constants for [Fe(phen) 3 ] 3+/2+ were close to those for [Fe(bpy) 3 ] 3+/2+ , suggesting the outer components of reorganization energies for both complexes are similar to each other. On the other hand, the reaction entropies for [Fe(phen) 3 ] 3+/2+ were smaller than those for [Fe(bpy) 3 ] 3+/2+ , reflecting the difference in the charge densities of complexes.