Dimethylglyoxime and Related Ligands

It has been noted (2) that many oxygen-carrying cobalt(II) complexes involve ligands that provide four donor atoms lying in the same plane as the cobalt atoms, such as salen , porphyrin and dimethylglyoxime, DMG, and related ligands. 

It has been observed (52) that Fe(DMG)2 readily takes up dioxygen in the presence of ligands such as pyridine, ammonia, histidine or imidazole bubbling nitrogen through the solution reverses the process 

The reversible oxygenation of Fe(DMG)2 (B)2 in aqueous dioxane solution, as monitored by reversible changes in the visible absorption spectrum and manometric oxygen evolution, has been reported (55), but in a more recent study 54) it was not possible to confirm the earlier findings. However it was established that there was a slow irreversible 

It is possible that steric factors prevent the formation of the bridging peroxide species in the case of vitamin Bj2,. (55), however, other cases have been reported (59) in which oxygenation proceeds no further than the formation of mononuclear peroxo radicals (i.e. first stage above). 

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