Synthesis, Characterization and Antimicrobial Activity of Schiff Bases Including Three Hydroxy Groups and Their CoCl 2 , PdCl 2 , CuCl 2 and ZnCl 2 Complexes

Four Schiff bases, (3/4/2/4)‐{[(2‐hydroxy‐5‐methylphenyl)imino]methyl}benzene‐1,2/1,3/1,4/1,2‐diols ( H 3 L 1 ‐ H 3 L 4 ), derived from 2,3/2,4/2,5/3,4‐dihydroxybenzaldehydes and 2‐amino‐4‐methylphenol, and their CoCl 2 , PdCl 2 , CuCl 2 and ZnCl 2 complexes were synthesized and characterized. The structures of the complexes were suggested on the basis of elemental analysis, TGA, molar conductivity, magnetic moment, FT‐IR, UV‐vis and NMR spectroscopy. According to the analytical and spectral data, the ligands H 3 L 1 , H 3 L 2 and H 3 L 3 acted as tridentate, giving chelate structures in the complexes, via the C=N nitrogen and two phenolate oxygen atoms whereas H 3 L 4 acted as bidentate. In addition, the crystal structure of H 3 L 1 was determined by X‐ray diffraction. The spectral data show that there is keto‐enol tautomerization in the ligands and keto form is dominant in H 3 L 1 and H 3 L 3 while enol form is in H 3 L 2 and H 3 L 4 . Antimicrobial activities of the compounds were tested against six bacteria and three fungi. [Zn( H 2 L 1 )Cl]⋅4H 2 O showed superior activity toward the fungi C. albicans , C. parapsilosis and C. tropicalis compared to H 3 L 1 and the other compounds. Strong activity of H 3 L 1 , H 3 L 2 and H 3 L 3 was observed toward S. aureus whereas they showed weak activity to the other microorganisms.