We describe, herein, the synthesis, full characterization, and optical properties of four different ligands L1-L4 which associate an azo group, an imidazole unit, and a Schiff base fragment. The UV-visible absorption bands are characteristic of π→π⁎ and n→π⁎ transitions with an additional charge transfer between the azobenzene moiety and the imino group. Finally the determination of MIC80 values against pathogenic fungi such as S. apiospermum, A. fumigatus, and C. albicans revealed that these ligands have effective antifungal properties with highest activities (MIC80) on C. albicans for the azole based ligands L1-L3. DPPH radical scavenging of the studied ligands was also tested.

Herein, to develop the comprehension of the microbiological activity of metal complexes based on benzaldehyde‐N4‐thiosemicarbazone derivatives, we described the synthesis, characterization of copper(II), zinc(II) and cadmium(II) complexes with vanillin‐4‐methylthiosemicarbazone (MTSVN) and 3,4‐dihydroxybenzaldehyde‐4‐methylthiosemicarbazone (MTSDHB). The crystal structures of the [ZnCl2(MTSVN)2] (L1 C1) and [CdBr2(MTSDHB)2.H2O]2 (L2C5) complexes were determined by the single X‐Ray diffraction method, the central ion is coordinated through the sulphur. For the other complexes, the ion is coordinated through the sulfur as well as azomethine nitrogen atom of the thiosemicarbazone. All these compounds, the two ligands and the new nine complexes were screened in vitro for their antifungal activity against human pathogenic fungi: Candida albicans and Aspergillus fumigatus, and for their antibacterial activity against Gram (+) bacteria such as Bacillus subtilis and Enterococcus faecalis as well as against Gram (−) bacteria such as Paracoccus yeei and Acinetobacter baumanii. By investigating the structure‐activity relationships, we found that the two ligands MTSVN (L1) exhibited significant effect against E. faecalis and A. baumanii and the MTSDHB (L2) acted only against E. faecalis. Furthermore, all the complexes (L1C1–L1C4 and L2C1–L2C5) showed significant antifungal and antibacterial activities against gram‐positive, gram‐negative bacteria, and two fungal human pathogens.

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The reactions of Cu (II), Zn (II) and Cd (II) chloride or bromide with (E)‐1‐(3,4‐dimethoxybenzylidene)‐4‐methylthiosemicarbazone (MTSVT) lead to the formation of new complexes. They were characterized by spectroscopic studies: IR, 1H and 13C NMR. The crystal structures of the compounds [MTSVT] (L), [ZnBr2(MTSVT)2] (2), [CdCl2(MTSVT)2] (3) and [CdBr2(MTSVT)2.H2O] (4) were determined by X‐ray diffraction. For complexes 2–4, the ion is coordinated through the sulfur atom. All compounds were tested for their antifungal activity against human pathogenic fungi Candida albicans and Aspergillus fumigatus, and for their antibacterial activity against Gram (+) Bacillus subtilis and Enterococcus faecalis as well as against Gram (−) bacteria such as Paracoccus yeei and Acinetobacter baumanii. The results indicated that the metal complexes exhibited a marked enhancement in antibacterial activity compared with the parent Schiff base.