Synthesis of Heptadentate Nitrogen-Oxygen Ligands (N₄O₃) with Substituting Groups and Determination of Stability Constants of Their Transition Metal(II) Complexes

Abstract

ABSTRACT.A new N4O3 heptadentate ligand, N,N'-Bis(2-hydroxybenzyl)-1,3-bis[(2-aminoethyl)amino]-2-propanol(H-BAP· 4HCl)was synthesized. The hydrochloric acid salts of Br-BAP·4HCl, Cl-BAP·4HCl, CH3O-BAP·4HCl and CH3-BAP·4HCl containing Br-, Cl-, H-, CH3O-and CH3-groups at the para-site of the phenol group of the H-BAP were synthesized. The structures of the ligands were confirmed by C. H. N. atomic analysis and 1 H NMR, 13 C NMR, UV-visible and mass spectra. The elemental stepwise protonation constants(logKn H ) of the synthesized N4O3 ligands showed six steps of the proton dissociation. The orders of the overall dissociation constants(logβp) of the ligands were Br-BAP < Cl-BAP < H-BAP < CH3O-BAP < CH3-BAP. The orders agreed well with that of Hammett substituent constants(σp). The calculated stability constants(logKML) between the ligands and transition metal ions agreed well with the order of the overall proton dissociation constants of the ligands but they showed a reverse order in Hammestt substituent constants(σp). The order of the stability constants between the transition metal ions with the ligands were Co(II) < Ni(II) < Cu(II) > Zn(II) > Cd(II) > Pb(II).