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Stabilities of the mixed-ligand complexes of Cu2+ ion with N,N,N′,N″,N″-pentamethyldiethylenetriamine [N,N,N′,N″,N″-pentamethyl-{bis(2-aminoethyl)amine}, Me5dien] as a primary ligand and α-alaninehydroxamic acid [2-amino-N-hydroxypropanamid, α-Alaha] or β-alaninehydroxamic acid [3-amino-N-hydroxypropanamid, β-Alaha] as a secondary ligand L and their absorption and EPR spectra at various pH values are reported. The visible spectra exhibit a characteristic red shift and a shoulder at lower energies indicating a five-coordinate structure of the formed complexes. The change of the EPR spectral parameters as a function of pH reflects two modes of an equatorial–axial chelation by the aminohydroxamic acid ligand L in the [Cu(Me5dien)(HL)]2+ and [Cu(Me5dien)(L)]+ species. [Copyright &y& Elsevier]

Abstract: Equilibrium studies of the mixed-ligand complexes of the copper(II) ion with pentamethyldiethylenetriamine (N,N,N′,N″,N″-pentamethyl-[bis(2-aminoethyl)amine], Me5dien) as a primary ligand and methioninehydroxamic acid (2-amino-4-(methylthio)butanehydroxamic acid, Metha) or histidinehydroxamic acid (2-amino-3-(4′-imidazolyl)propanehydroxamicacid, Hisha) as a secondary ligand L were performed by potentiometric titration, UV–Vis and EPR spectroscopy. The results show that in these ternary systems the dinuclear [Cu2(Me5dien)L2H−1]+ mixed-ligand species is formed as a predominant one in the basic solution. The monouclear [Cu(Me5dien)L]+ species is formed in low concentration. Our spectroscopic results indicate that the geometry of these mixed-ligand five-coordinate complexes is strongly distorted towards trigonal-bipyramidal. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]