Synthesis, characterization, and electrochemical behavior of mixed-ligand complexes of cobalt(III) with dimethylglyoxime and some amino acids

The syntheses of non-electrolyte complexes of the general formula [Co(Hdmg)(2)(HA)X], where Hdmg=dimethylglyoximato monoanion, HA = glycine (Gly), Serine (Ser), Cysteine (Cys) or Cystine (Cys-Cys) and X = Cl, Br, I, SCN are described. The structure of the complexes proposed according to elemental analyses, IR, UV-Visible and H-1 NMR spectra is pseudo-octahedral. The cyclic voltammograms in DMSO at a GC disk electrode consist of two processes (I and II) corresponding to oxidations, whereas the redox systems III and IV appear to be associated with reduction processes. The Co(II)/Co(I) redox couple is reversible for various complexes and is relatively insensitive to the axial ligand. The Co(III)/Co(II) couple depends on the axial ligation, shows chemical irreversibility and has a much slower rate of electron transfer than the Co(II)/Co(I) couple due to the strong binding of the Lewis base to the Co(III) ion.