Synthesis, spectroscopic, photoluminescence properties and biological evaluation of novel Zn(II) and Al(III) complexes of NOON tetradentate Schiff bases

Abstract Novel mononuclear Zn(II) and Al(III) complexes were synthesized from the reactions of Zn(OAc) 2 ·2H 2 O and anhydrous AlCl 3 with neutral N2O2 donor tetradentate Schiff bases; N,N′bis(salicylaldehyde)4,5-dimethyl-1,2-phenylenediamine (H 2 L 1 ) and N,N′bis(salicylaldehyde)4,5-dichloro-1,2-phenylenediamine (H 2 L 2 ). The new complexes were fully characterized by using micro analyses (CHN), FT-IR, 1 H NMR, UV–Vis spectra and thermal analysis. The analytical data have been showed that, the stoichiometry of the complexes is 1:1. Spectroscopic data suggested tetrahedral and square pyramidal geometries for Zn(II) and Al(III) complexes, respectively. The synthesized Zn(II), and Al(III) complexes exhibited intense fluorescence emission in the visible region upon UV-excitation in methylene chloride solution at ambient temperature. This high fluorescence emission was assigned to the strong coordination of the ligands to the small and the highly charged Zn(II) and Al(III) ions. Such strong coordination seems to extend the π-conjugation of the complexes. Thermal analysis measurements indicated that the complexes have good thermal stability. As a potential application the biological activity (e.g., antimicrobial action) of the prepared ligands and complexes was assessed by in-vitro testing of their effect on the growth of various strains of bacteria and fungi.