Synthesis and characterization of metal complexes with N, N″-bis(2-hydroxybenzyl)-diethylenetriamine- 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 new multidentate ligand, N, N″-bis(2-hydroxybenzyl)-diethyl- enetriamine - N, N′, N″-triacetic acid (HBDT) are described. Protonation constants of the ligand and stability constants of its 1:1 complexes with trivalent and divalent metal ions are determined by potentiometric, spectrophotometric methods and by potentiometric determination of ligand-ligand competition. The stabilities of complexes formed by the trivalent ions Fe 3+, Ga 3+ and In 3+ with HBDT are compared with those of structurally related ligands. While this new octadentate ligand, which contains two phenolate donor groups, 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 also contains two phenolate donor groups. The difference is rationalized on the basis of ligand structure and the probable arrangement of donor groups around the metal center.