Experimental and calculation methods of studying the effect of second coordination sphere on standard rate constants of charge transfer for Cr(III)/Cr(II) redox couple in chloride melts

摘要

The cyclic voltammetry method was used to determine the standard rate constants of charge transfer (k _s) on a glassy carbon electrode for the Cr(III)/Cr(II) redox couple in the systems of NaCl-KCl-CrCl_3, KCl-CrCl_3, and CsCl-CrCl_3 in the temperature range of 973-1173 K. It was shown that k _s grows at an increase in the temperature and decreases as sodium cations are replaced by potassium and cesium cations in the second coordination sphere of chromium complexes. The calculations carried out using the PC GAMESS/Firefly quantum-chemical software by means of the DFT technique showed that the values of the charge transfer activation energy change monotonously in the series of Na-K-Cs in accordance with the ratio of reorganization energies. In its turn, this leads to monotonous variation of the charge transfer rate constants.