ECE mechanism as a tool for the investigation of unstable metal complexes: Part I. Electrochemical reduction of trans-[CoBr2(N)4]+-type complexes on the mercury electrode

A polarographic investigation of trans-CoBr₂(N)₄]⁺-type complexe where (N)₄ represents (NH₃)₄, (ethylenediamine)₂ and (propylenediamine)₂, has been carried out in acetate buffer solutions. These complexes gave two polarographic waves; the first wave corresponds to the reduction of Co(III) to Co(II) and the second to the reduction of Co(II) to Co(0). The relation between current and time of the first wave in a positive potential is dependent on the dissolution wave due to bromide ions produced by acid hydrolysis and parallel ECE mechanism. Overall reaction is as follows: at the electrode surface, Co(III)Br₂(N)₄]⁺+e^-→Co(II)Br₂(N)₄] Co(II)Br₂(N)₄]+6H₂O→Co(II)(H₂O₆]²⁺+2Br^-+(N)₄ 2Br^-+2Hg→Hg₂Br₂+2e and in the solution, Co(III)Br₂(N)₄]⁺+2H₂O→Co(III)(H₂O₂(N)₄]³⁺+2Br^-The effects of the acid hydrolysis of a tervalent cobalt complex on the current—potential curve were simulated.