Effect of the ionic strength on the redox reaction of dicyanobis(bipyridine)iron(III)‐iodide in binary and ternary solvent systems

The redox reaction between dicyanobis(bipyridine)iron(III) and iodide ion follows first‐order kinetics in 10% (v/v) tertiary butyl alcohol‐water. The reaction was found first and zero order in iodide and dicyanobis(bipyridine)iron(III), respectively, at 0.06 M ionic strength and 293 ± 1 K. The thermodynamic parameters of activation such as EA (16.07 kJ mol−1), A (1 × 10−4 M s−1), ΔH# (13.6 kJ mol−1), ΔS# (−329.81 J K−1 mol−1), and ΔG# (90.1 kJ mol−1) were determined. The effect of the ionic strength on the rate constant leads to recognizing the stabilization or destabilization of the transition state complex that forms during the rate‐determining step of the reaction. The value of the zero‐order rate constant was decreased with increasing ionic strength that yielded a negative value of the slope in each binary and ternary solvent systems. This negative sign refers to the electron transfer between opposite charge carriers such as [FeIII(bpy)2(CN)2]+ and I− during the rate‐determining step. The destabilization of the transition state complex is surfaced by the increasing slope, that is, 5