Electrochemical Kinetic Parameters of Geometric Isomers of Singly Charged Cobalt(III) Complexes

Abstract

Abstract The kinetic parameters of electrode reactions of several geometric isomers of singly charged cobalt(III) complexes have been determined by means of Tast polarography. The complexes studied are trans-[Co(NCS)(NO2)(en)2]Cl·H2O, cis-[Co(NCS)(NO2)(en)2]Cl·2H2O, trans-[Co(NO2)2(en)2]NO3, cis-[Co(NO2)2(en)2]NO3, trans-[Co(NO2)2(NH3)4]NO3·0.5H2O, cis-[Co(NO2)2(NH3)4]NO3, trans-[CoCl(NO2)(en)2]NO3, and cis-[CoCl(NO2)(en)2]NO3. These complexes showed two irreversible reduction waves; the first corresponds to CoIII→CoII, and the second, to CoII→Co0. The electrochemical kinetic parameters for the one-electron reduction wave were obtained in 0.1 and 1.0 M acetate buffer solutions. The half-wave potentials for the first wave of the complexes were more positive for the cis isomers than for the corresponding trans isomers. The cathodic rate constants at E=0 for the cis isomers were also larger than those for the corresponding trans isomers. A slight increase in the rate constant with the decrease in ionic strength was observed.