Ternary copper(II) complexes with diethylenetriamine and α-(or β-) alaninehydroxamic acids in water solution

Abstract

Stabilities of the mixed-ligand complexes of Cu 2+ ion with diethylenetriamine [bis(2-aminoethyl) amine, dien)] 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 aminohydroxamic acid ligand L in [Cu(dien)(HL)] 2+ and [Cu(dien)(L)] + species, while the diethylenetriamine nitrogens are coordinated at three equatorial positions in each case. α-Alaha is a more effective chelating ligand than β-Alaha in the Cu 2+-dien-L ternary system. This is reflected in the much higher basicity-adjusted stability constants, logK Cudien)(α-Alaha)(β-Alaha) ∑pK H.