Synthesis and characterization of polydentate schiff-base ligands and their complexes

In this study, we synthesized the amine compounds 2-{(E)-[(2-aminoethyl) imino]methyl}phenol (H₃A) and 2-{(E)-[(3-aminopropyl)imino]methyl}-6- methoxyphenol (H₃B) as the starting materials. From reactions of the starting materials with 2-hydroxy-5-methylisophthalaldehyde, phthalaldehyde, and 2-hydroxy-5-t-butylisophthalaldehyde, we prepared the new ligands H ₃L¹-H₃L³ and H₂L. The Cu(II) and Cd(II) complexes of the ligands have been obtained. Microanalytical data, magnetic moment, ¹H(¹³C) NMR, mass spectra, FT-IR, and conductivity measurements have been used to explain the structures of the ligands and their complexes. The protonation constants of the ligands H ₃L¹-H₃L³ have been studied in a 1:1 molar ratio (M:L). Protonation and stability constants of the Schiff bases and their Cu(II) and Cd(II) complexes have been determined by the potentiometric titration method in 50% dioxane-water media at 25.00 ± 0.02°C under a nitrogen atmosphere and ionic strength of 0.1M NaClO₄. The ligands H₃L1-H₃L³ have seven protonation constants. In other words, the ligand H₂L has six protonation constants. The variation of protonation constants of these compounds were interpreted on the basis of structural effects exposed by the substituents.