Unexpected formation of the copper(II) dinuclear mixed-ligand species in the ternary system of N,N,N′,N″,N″-pentamethyldiethylenetriamine with methionine- or histidinehydroxamic acids in aqueous solution

Equilibrium studies of the mixed-ligand complexes of the copper(II) ion with pentamethyldiethylenetriamine (N,N,N 0 ,N 00 ,N 00 -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 0 -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. � 2007 Elsevier Ltd. All rights reserved.