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

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))center dot CH3OH (1) and Co(papH (1))(MEA)(2)center dot 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 -CH2-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). (C) 2010 Elsevier B. V. All rights reserved.