Potentiometric titration study of two novel polydenate ligands and investigations of their complexes

Abstract

Two novel linear polyamine ligands, N,N'-bis-(2-(N''-2-hydroxyl-5-bromobenzyl)aminoethyl) malondiamide (L1) and N,N'-bis-(3-(N''-2-hydroxyl-5-bromobenzyl)aminopropyl) malondiamide (L2), have been synthesized and fully characterized by elemental analysis (1H NMR and IR spectroscopy) (Fig. 1). The binding ability of ligands L1 and L2 to metal ions such as Cu(II), Zn(II), Co(II), Mn(II), Mg(II), and Ca(II) has been investigated by the potentiometric method in 1,4-dioxane–water (v/v = 15:100) and KNO3 (0.1 mol dm–3) at 25.0°C. In view of the linear structures of L1 and L2, binuclear metal complexes can be formed in solution by controlling Cu(II)-5-substituted o-phenanthroline (Rphen, R = CH3, H, Cl, NO2):L to a 2:1 molar ratio, whereas the mononuclear metal complexes form at molar ratio M(II):L of 1:1, where M(II) is Cu(II), Zn(II), Co(II), Mn(II), Mg(II), and Ca(II). The stability constants of metal complexes have been determined and further discussed. In addition, two manganic complexes have been synthesized and IR and electronic spectra showed their coordination nature.Key words: linear polyamine ligand, 5-substituted o-phenanthroline, mononuclear and binuclear metal complex, stability, spectrum.