Electrochemical reaction of tris(1,10-phenanthroline)iron complexes in some amide-type ionic liquids

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)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 apparent 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.