The polarography of trans-cobalt(III) complexes of tetradentate Sciff bases and .ALPHA.-methylbenzylamine in N,N-dimethylformamide and methanol solutions.
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The polarographic behavior of mixed-ligand cobalt(III) complexes of tetradentate Schiff bases and α-methylbenzylamine (pheNH<SUB>2</SUB>) of the general formula of [CoZ(pheNH<SUB>2</SUB>)<SUB>2</SUB>]<SUP>+</SUP> in methanol and <I>N</I>,<I>N</I>-dimethylformamide solutions was studied. At the dropping mercury electrode, these metal complexes give well-defined, two-step waves corresponding to the reduction of cobalt (III) to cobalt(II) and that of cobalt(II) to cobalt(I). A careful and systematic study of their polarographic behavior revealed that the reaction mechanism in the presence of uncomplexed pheNH<SUB>2</SUB> can be formulated as:<BR>& [CoZ(pheNH_2)_2]^++e^-\rightleftarrows[CoZ(pheNH_2)_2]^0<BR>& [CoZ(pheNH_2)_2]^0+e^-\rightleftarrows[CoZ(pheNH_2)_2]^-<BR>while, in the absence of pheNH<SUB>2</SUB>, the reaction mechanism for the second step of the <I>N</I>,<I>N</I>′-ethylenebis(acetylacetoneiminato) and <I>N</I>,<I>N</I>′-ethylenebis(benzoyIacetoiminate) systems is given by:<BR>[CoZ(pheNH_2)_2]^0+e^-\rightleftarrows[CoZ(pheNH_2)]^-+pheNH_2<BR>This can be ascribed to the labile nature of the axial ligand, pheNH<SUB>2</SUB>, in these two complexes. The introduction of halogen atoms on the methyl or methylene carbon of <I>N</I>,<I>N</I>′-ethylenebis(acetylacetoneiminato) and that of the benzene ring on the framework of the equatorial ligand remarkably shifted the half-wave potential towards more positive potentials. This fact suggests the electron withdrawal from the cobalt atom by these groups. Furthermore, by examining the nature of the half-wave potentials the redox orbitals of <I>N</I>,<I>N</I>′-ethylenebis(salicylideneaminato) and <I>o</I>-phenylenebis(salicylideneaminato) systems were concluded to be essentially different from those of other Schiff-base systems.
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