A polarographic investigation of the reduction mechanism of certain cobalt (III) complex ions

A series of eight compounds with bis-diamine cores were prepared and their electrochemical behavior was explored polarographically. The behavior of the compounds was studied at the dropping mercury electrode and the rotating platinum electrode.

Trans-dinitro-bis-(ethylenediamine) cobalt (III) nitrate shows reversible behavior in well-buffered solutions at the dropping mercury electrode, The mechanism for the reduction is proposed as; rapid, reversible election transfer; decomposition of the reduced species; and, in solutions sufficiently alkaline, the formation of tris-(ethylenediamine) cobalt (II), thereby accounting for the observed second wave.

The reduction of cis dithiocyanato-bis-(ethylenediamine) cobalt (III) thiocyanate and oxalato-bis-(ethylenediamine) cobalt (III) chloride both give irreversible waves, thereby complicating any proposal of a mechanism. The observed second reduction wave, though, appears to be caused by the formation of tris-(ethylenediamine) cobalt (II), as in the case of the dinitro compound.

A proposal of the mechanism for the other five compounds was not possible as they either reduced at too positive a potential, aquated too rapidly, or both.