Abstract
The bis-Schiff bases of N2O2 dibasic ligands, H2La and H2Lb are synthesized by the condensation of ethylenediamine (a) and trimethylenediamine (b) with 6-formyl-7-hydroxy-5-methoxy-2-methylbenzo-pyran-4-one. The ligands are characterized using elemental analysis, IR, UV–Vis, 1H-NMR and mass spectroscopy. The ionization constant pKa values are determined spectrophotometrically. The 1H-NMR spectra of the ligands show the presence of phenolic coordinating groups. New complexes of H2La and H2Lb with metal ions Cr(III), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) are synthesized. Elemental analyses, infrared, ultraviolet-visible, electron spin resonance and thermal analysis, as well as conductivity and magnetic susceptibility measurements, are used to elucidate the structures of the newly prepared metal complexes. Thermal degradation studies for some complexes show that the final product is the metal oxide. A square planar geometry is suggested for the Cu(II), Zn(II) (for H2La and H2Lb) and Ni(II) (for H2La) complexes; an octahedral geometry for the Co(II), Cr(III), Fe(III) (for H2La and H2Lb), and Ni(II) (for H2Lb) complexes. The coordination sites are two azomethine nitrogens and two phenolic oxygens in the tetradentate Schiff bases.