Synthesis of cobalt(III) complexes with novel open chain oxime ligands and metal–ligand coordination in aqueous solution

Abstract Cobalt(III) complexes with new open chain oxime ligands: N,N′-bis(2-hydroxyiminopropionyl)-1,2-aminoethane ( H 2 pen ) and N,N′-bis(2-hydroxyiminopropionyl)-1,3-diaminopropane ( H 2 pap ) have been investigated. Single crystals of Co(papH −1 )(Im 2 )·CH 3 OH ( 1 ) and Co(papH −1 )(MEA) 2 ·1.5H 2 O ( 2 ) (where Im = imidazole, MEA = monoethanolamine) suitable for X-ray crystallography were grown by slow evaporation of methanol/water solutions at room temperature. The molecular structures have been determined using single-crystal X-ray diffraction methods. The potentiometric and spectrophotometric results in aqueous solution reveal that both of the open chain ligands show a very high efficacy in the coordination of Co(II) ions. As it has been indicated, differences between the two oxime ligands in complexing ability may be attributed to the longer –CH 2 – chain in H 2 pap and by that a better fit of the relatively large Co(II) ion to the accessible binding site. One of the complex species confirmed under inert atmosphere, namely of type Co(LH −1 ) − (where L = pap or pen), has been shown as the “active” form, capable of dioxygen uptake followed by irreversible oxidation to Co(III).