Five Cd(II) complexes with the anion of 5-NO₂-salicylaldehydeH (5-NO₂-saloH) in the absence or presence of the α-diimine 1,10-phenanthroline (phen), 2,2′-dipyridylamine (dpamH), 2,2′-dipyridine (bipy), or 2,9-dimethyl-1,10-phenanthroline (neoc) were synthesized and characterized as [Cd(5-NO₂-salo)₂(CH₃OH)₂] (1), [Cd(5-NO₂-salo)₂(phen)]·2CH₃OH·H₂O (2), [Cd(5-NO₂-salo)₂(dpamΗ)] (3), [Cd₃(5-NO₂-salo)₆(bipy)₂] (4), and [Cd(5-NO₂-salo)(neoc)(NO₃)]₂ (5). Based on spectroscopic results (IR, UV, NMR), elemental analysis and conductivity measurements an octahedral geometry around cadmium metal ion is suggested, with the 5-NO₂-salicylaldehyde ligand having different coordination modes. The structures determined by X-ray crystallography verified neutral mononuclear 1–3 and trinuclear 4. Simultaneous TG/DTG–DTA technique was used to analyze the thermal behavior of 1, 2 , and 3. The complexes bind tightly to calf-thymus DNA mainly by intercalation, as concluded by DNA viscosity measurements and exhibit significant displacement of EB from the EB-DNA complex.

Copper(II) complexes with an α-diimine show a wide variety of biological activities, such as antibacterial, antifungal, antioxidant and anticancer. In this work, we synthesized and structurally characterized two novel Cu(II) complexes with methyl 3-formyl-4-hydroxybenzoate (HL) and α-diimines: 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen). Crystal structure analysis shows that the formulas of the compounds are [Cu(bipy)(L)(BF₄)] (1) and [Cu(phen)(L)(H₂O)](BF₄)·H₂O (2), with BF₄ ⁻ as a ligand in complex 1, which is rarely coordinated to metals. Both complexes have a square pyramidal geometry, while DFT calculations showed that the most stable structures of complexes 1 and 2 in a water/DMSO mixture are square-planar derivatives [Cu(bipy)(L)]⁺ and [Cu(phen)(L)]⁺. The antibacterial activity of compounds was evaluated in vitro on four Gram-negative and four Gram-positive bacterial strains. Complex 2 showed greater antibacterial activity towards all bacterial strains comparable to the control compound Amikacin. Complex 2 exerted a strong cytotoxic effect against the tested cancer cell lines (IC₅₀ values ranging from 0.32 to 0.44 μM). Both complexes caused apoptotic cell death in HeLa cells and a noticeable in vitro antiangiogenic effect. In the concentration range of 5 to 100 μM, the complexes showed the absence of a genotoxic effect and displayed a protective effect against oxidative DNA damage induced by H₂O₂ in human peripheral blood cells. The interaction between the compounds and calf–thymus DNA was evaluated by diverse techniques suggesting a tight binding, which was also confirmed by molecular docking. In addition, it was found that the complexes bind tightly and reversibly to bovine and human serum albumin.

Pentagonal-bipyramidal isothiocyanato Co(II) and Ni(II) complexes with condensation product of 2,6-diacetylpyridine and trimethylammoniumacetohydrazide (Girard’s T reagent) were synthesized and characterized by elemental analyses, IR and UV–vis spectra, molar conductivity, and magnetic susceptibility. Crystal structures of the Co(II) and Ni(II) complexes were also determined. Antimicrobial activities of the ligand and metal complexes were examined.