Synthesis of N-hydroxybenzylethylenediamine- N, N′, N′-triacetic acid and the stabilities of its complexes with divalent and trivalent metal ions

Abstract

The synthesis, characterization and metal ion affinities of a multidentate ligand, N-hydroxybenzylethylenediamine- N, N′, N′-triacetic acid (HBET) are described. Protonation constants of the ligand and stability constants of its complexes with trivalent and divalent metal ions are determined by direct potentiometric measurement of p[H] and by potentiometric measurement of ligand-ligand competition. The stabilities of complexes formed by the trivalent ions, Fe 3+, Ga 3+ and In 3+ with HBET are compared with those of structurally related ligands. While this ligand, which contains one phenolate donor group, forms stable complexes with trivalent metal ions, its stability constants are significantly lower than those of hexadentate N, N′-bis(2-hydroxybenzyl)-ethylenediamine- N, N′-diacetic acid (HBED) which contains two phenolate donor groups. The difference is rationalized on the basis of the strength of coordination of these metal ions by phenolate donor groups.