1‐phenyl‐3‐methyl‐4‐benzoyl‐5‐pyrazolone 4‐ethyl‐thiosemicarbazone (HL) and its copper(II), vanadium(V) and nickel(II) complexes: [ Cu ( L )( Cl )]·C₂H₅OH·(1), [ Cu (L)₂]· H₂O (2), [ Cu ( L )( Br )]· H₂O ·CH₃OH (3), [ Cu ( L )( NO ₃)]·2C₂H₅OH (4), [VO₂(L)]·2 H₂O (5), [ Ni ( L )₂]· H₂O (6), were synthesized and characterized. The ligand has been characterized by elemental analyses, IR, ¹H NMR and ¹³C NMR spectroscopy. The tridentate nature of the ligand is evident from the IR spectra. The copper(II), vanadium(V) and nickel(II) complexes have been characterized by different physico‐chemical techniques such as molar conductivity, magnetic susceptibility measurements and electronic, infrared and electron paramagnetic resonance spectral studies. The structures of the ligand and its copper(II) (2, 4), and vanadium(V) (5) complexes have been determined by single‐crystal X‐ray diffraction. The composition of the coordination polyhedron of the central atom in 2, 4 and 5 is different. The tetrahedral coordination geometry of Cu was found in complex 2 while in complex 4, it is square planar, in complex 5 the coordination polyhedron of the central ion is distorted square pyramid. The in vitro antibacterial activity of the complexes against Escherichia coli, Salmonella abony, Staphylococcus aureus, Bacillus cereus and the antifungal activity against Candida albicans strains was higher for the metal complexes than for free ligand. The effect of the free ligand and its metal complexes on the proliferation of HL‐60 cells was tested.

Due to the structure of acylhydrazones both by the pharmacophore –CO–NH–N= group and by the different substituents present in the molecules of compounds of this class, various pharmacological activities were reported, including antitumor, antimicrobial, antiviral, antiparasitic, anti-inflammatory, immunomodulatory, antiedematous, antiglaucomatous, antidiabetic, antioxidant, and actions on the central nervous system and on the cardiovascular system. This fragment is found in the structure of several drugs used in the therapy of some diseases that are at the top of public health problems, like microbial infections and cardiovascular diseases. Moreover, the acylhydrazone moiety is present in the structure of some compounds with possible applications in the treatment of other different pathologies, such as schizophrenia, Parkinson’s disease, Alzheimer’s disease, and Huntington’s disease. Considering these aspects, we consider that a study of the literature data regarding the structural and biological properties of these compounds is useful.

Thirty two new Cu(II), Ni(II) and Zn(II) complexes (1–32) with salicylidene thiosemicarbazones (H₂L¹–H₂L ¹⁰) were synthesized. Salicylidene thiosemicarbazones, of general formula (X)N-NH-C(S)-NH(Y), were prepared through the condensation reaction of 2-hydroxybenzaldehyde and its derivatives (X) with thiosemicarbazide or 4-phenylthiosemicarbazide (Y = H, C₆H₅). The characterization of the new formed compounds was done by ¹H-NMR, ¹³C-NMR, IR spectroscopy, elemental analysis, magnetochemical, thermoanalytical and molar conductance measurements. In addition, the structure of the complex 5 has been determined by X-ray diffraction method. All ligands and metal complexes were tested as inhibitors of human leukemia (HL-60) cells growth and antibacterial and antifungal activities.

5‐methoxy‐2‐(((2chloro‐5‐(trifluoromethyl)phenyl)imino)methyl)phenol) (HL) and its cobalt (II), copper (II), manganese (II), nickel (II), palladium (II), and platinum (II) complexes, [Co(L)₂]·4H₂O (1), [Cu(L)₂] (2), [Mn(L)₂(H₂O)₂]·H₂O (3), [Ni(L)₂] (4), [Pd(L)₂] (5), [Pt(L)₂] (6), were synthesized and characterized. The compounds were investigated by different physico‐chemical techniques including IR, ¹H‐NMR, ¹³C‐NMR, UV‐Vis, mass spectroscopies, elemental and thermal analysis, magnetic susceptibility measurements, and molar electric conductivity. The molecular structures of the HL ligand and copper (II), nickel (II), and palladium (II) complexes were confirmed by X‐ray crystallography analysis on the monocrystal. Each metal ion, in these complexes, is four‐coordinated in N₂O₂ coordination environment. The coordination geometry of Ni²⁺ and Pd²⁺ is square planar due to cystallographically imposed inversion symmetry of the metal centers, and the coordination geometry of copper atom can be described as tetrahedrally distorted square planar. The assessed toxicity of the ligand and its complex combinations on plant cell of Triticum aestivum L. were macroscopically and microscopically consistent. The same substances were investigated for the animal cell toxicity on crustacean Artemia franciscana Kellogg, and Mn²⁺ complex did not record any lethal effect.

Hydrazone complexes of Cu(II), Co(II), Zn(II), Ni(II) and Pt(II) with N-isonicotinoyl-N′-(3-metoxy-2 hydroxybenzaldehyde)-hydrazone (HL) were synthesized and characterized by different physico-chemical techniques including elemental and thermal analysis, magnetic susceptibility measurements, molar electric conductivity, as well as IR (infrared), ¹H-NMR and ¹³C-NMR (hydrogen and carbon nuclear magnetic resonance, UV-Vis (ultraviolet-visible), FAB (fast atom bombardment), EPR (electron paramagnetic resonance), and mass spectroscopies. The crystal structure of ligand was determined by single crystal X-ray diffraction studies. Spectral data showed that hydrazone behaves as an ONO tridentate ligand through the azomethine nitrogen, phenolate and keto oxygen atoms. For the copper(II) complexes, metal–ligand bonding parameters were evaluated from the EPR spectra. These parameters indicate the presence of in-plane π bonding. In addition, the f values of complexes 1–4 indicate small distortion from planarity. The effect of these complexes on proliferation of human breast cancer (MCF-7 and SKBR-3), human melanoma (A375), lung adenocarcinoma cells (NCI-H1573) and their antibacterial activity against Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus and Candida albicans strains were studied and compared with those of free ligand. The ligand and complexes 1–3 showed significant antimicrobial activity against the Gram-positive bacteria Staphylococcus aureus and Candida albicans in comparison to the control drugs. The complexes 2–4 could be potential antitumor agents, leading to a significant improvement of the cytotoxic activity when compared with HL.

A novel Schiff base, ethyl 4-[(E)-(2-hydroxy-4-methoxyphenyl)methylene-amino]benzoate (HL), was prepared and structurally characterized on the basis of elemental analyses, ¹H NMR, ¹³C NMR, UV-Vis and IR spectral data. Six new copper(II) complexes, [Cu(L)(NO₃)(H₂O)₂] (1), [Cu(L)₂] (2), [Cu(L)(OAc)] (3), [Cu₂ (L)₂Cl₂(H₂O)₄] (4), [Cu(L)(ClO₄)(H₂O)] (5) and [Cu₂(L₂S)(ClO₄)(H₂O)]ClO₄·H₂O (6) have been synthesized. The characterization of the newly formed compounds was done by IR, UV-Vis, EPR, FAB mass spectroscopy, elemental and thermal analysis, magnetic susceptibility measurements and molar electric conductivity. The crystal structures of Schiff base and the complex [Cu₂(L₂S)(ClO₄)(H₂O)]ClO₄·H₂O (6) have been determined by single crystal X-ray diffraction studies. Both copper atoms display a distorted octahedral coordination type [O₄NS]. This coordination is ensured by three phenol oxygen, two of which being related to the µ-oxo-bridge, the nitrogen atoms of the azomethine group and the sulfur atoms that come from the polydentate ligand. The in vitro antimicrobial activity against Escherichia coli ATCC 25922, Salmonella enteritidis, Staphylococcus aureus ATCC 25923, Enterococcus and Candida albicans strains was studied and compared with that of free ligand. The complexes 1, 2, 5 showed a better antimicrobial activity than the Schiff base against the tested microorganisms.