Mixed-ligand zinc(II) complexes with diethylenetriamine (or triethylenetetramine) and α-(or β-) alaninehydroxamic acids in water solution. Potentiometric and NMR studies

Abstract

Stabilities of the mixed-ligand complexes of Zn II ion with diethylenetriamine [bis(2-aminoethyl)amine, dien) or triethylenetetramine [ethylenebis(2′-aminoethylamine, trien] as a primary ligand A 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 NMR behaviour are reported. The NMR spectra show that in the binary systems α- and β-Alaha are capable of binding zinc(II) in either (O,O) or (N,N) chelating mode. In contrast, in the ternary systems both behave as simple hydroxamic acids, thus, co-ordinate zinc(II) exclusively through the oxygens of the hydroxamate groups. This is reflected in the same basicity-adjusted stability constants, log K Zn(dien)(α-Alaha)(β-Alaha)−p K NHOH micro .