Coordination modes of histidine- or methioninehydroxamic acids in copper(II) mixed-ligand complexes with ethylenediamine in aqueous solution

The stability constants and coordination modes of the mixed-ligand complexes formed by copper(II) ion and ethylenediamine as a primary ligand and methioninehydroxamic acid (Metha) or histidinehydroxamic acid (Hisha) as a secondary ligand L were determined by potentiometric titration, UV–Vis and EPR spectroscopy. The obtained results suggest the formation of mixed-ligand species in basic solution with 4N coordination – both amine and hydroxamic nitrogens of Metha or Hisha (NH2, Nha) and two amine nitrogens of en (2 × NH2) in the equatorial plane.

Equilibrium studies of the mixed-ligand complexes of the copper(II) ion with ethylenediamine and methionine- or histidinehydroxamic acid show that the mixed-ligand species is formed in the basic solution. Their absorption and EPR spectra indicate 4N coordination – both amine and hydoxamic nitrogens of aminohydroxamic acid and two amine nitrogens of ethylenediamine in the equatorial plane. The weak interactions between thioether sulfur of methioninehydroxamic acid or imidazole ring of histidinehydroxamic acid and copper(II) ion are suggested.Figure optionsDownload as PowerPoint slide