Nano-synthesis, spectroscopic characterization, quantum chemical calculations, thermal properties and antimicrobial activity of (E)-N′-(2-hydroxybenzylidene)morpholine-4-carbothiohydrazide ligand and its metal complexes

The (E)-N′-(2-hydroxybenzylidene)morpholine-4-carbothiohydrazide (H₂L) ligand and its chelates with Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) have been synthesized. Analytical and spectral data prove that the ligand acts a monobasic tridentate ligand coordinated via deprotonated phenolic O, azomethine N and thione S atoms (ONS chromophore) with cobalt(II), nickel(II) and copper(II) salts leading to two fused five and six-membered chelate rings. While with zinc(II) and cadmium(II) salts the ligand behaves as a neutral bidentate and coordinated through the azomethine nitrogen and thione sulfur (NS type). The percent of weight losses during thermal degradation processes are in agreement with the proposed formulae as indicated by the TG/DTG studies. The X-ray diffraction patterns (XRD) indicate nano-sized particles and crystalline nature of the free organic ligand as well as all of its metal complexes. The corresponding predicted spectral data of H₂L and its metal chelates were calculated in the Polarizable Continuum Model (PCM) using DFT and DT-DFT methods at the B3LYP/LanL2DZ level of theory. The obtained results showed a relatively good agreement between the experimental and predicted spectral data. The in vitro antibacterial and antifungal properties of the H₂L and its metal complexes against four bacteria, Gram-positive (Staphylococcus aureus and bacillus subtilis) and gram-negative (Escherichia coli and proteus vulgaris) and two strains of fungus (Aspergillus fumigatus and candida albicans) showed that metal chelates exhibit more inhibitory effects than the free ligand. Selectivity is detected in the activities of some compounds over certain microorganisms, which is important for future pharmaceutical applications.