Effect of the Second Coordination Sphere on the Standard Rate Constants of Charge Transfer for the Cr(Ⅲ)/Cr(Ⅱ) Redox Couple in Chloride Melts

摘要

The cyclic voltammetry method was used to determine thestandard rate constants of charge transfer (k_s) on a glassy carbonelectrode for the Cr(Ⅲ)/Cr(Ⅱ) redox couple in the NaCl–KCl–CrCl_3, KCl–CrCl_3, and CsCl–CrCl_3 melts in the temperature rangeof 973–1173 K. It was shown that k_s increases with an increase intemperature and decrease as sodium cations are replaced bypotassium and cesium cations in the second coordination sphere ofchromium complexes.Optimized geometrical structures and energies of such modelparticles as (M~+)_n[Cr(Ⅲ)Cl_6]~(3-) and (M~+)_n[Cr(Ⅱ)Cl_6]~(4-) (M - Na, K,Cs; n=1 - 6) were obtained by quantum-chemical calculations. Themost stable compositions of these particles are determined. Basedon the calculated reorganization energies the activation energies ofcharge transfer have been computed. These values changemonotonously in the Na–K–Cs series in accordance with the ratioof reorganization energies: E_(act) (Na)