Synthesis and spectroscopic studies on ternary bis-Schiff-base complexes having oxygen and/or nitrogen donors

Abstract

The bis-Schiff-base of N2O2 donor dibasic ligand, H2L, is synthesized by the reaction of 4,6-diacetylresorcinol with ethylamine in molar 1 : 2 ratio. The ligand is characterized using IR, UV-Vis, 1H NMR and mass spectroscopy. The 1H NMR spectrum of the ligand shows the presence of phenolic coordinating groups. Several new mixed ligand complexes of the Schiff-base ligand (H2L) and (L′) where (L′) = deprotonated 8-hydroxyquinoline (8-HQ), 2,2′-bipyridine (2,2′-Biby) and 1,10-phenanthroline (1,10-Phen) with different metal ions such as Co(II), Ni(II), Cu(II) and UO2(VI) 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. The complexes are isolated as binuclear and confirmed by ESR spectra. Thermal degradation studies for some complexes show that the final product is the metal oxide. In addition, thermal gravimetric analysis (TGA) is used as a tool to detect that the water molecules associated with the complexes are either coordinated or crystalline. An octahedral geometry is suggested for the Co(II), Ni(II), Cu(II) (for 2,2′-Biby and 1,10-Phen), and UO2(VI) complexes, square planar for Cu(II) (for 8-HQ) complexes and their calculated field parameters agree with their proposed geometry.