Synthesis, characterization, biological activity and equilibrium studies of metal(II) ion complexes with tridentate hydrazone ligand derived from hydralazine

In the present study, a new hydrazone ligand (2-((2-phthalazin-1-yl)hydrazono)methyl)phenol) prepared by condensation of hydralazine (1-Hydralazinophthalazine) with salicylaldehyde (SAH). The synthesized SAH-hydrazone and its metal complexes have been characterized by elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance, mass spectra, UV–vis and thermal analysis (TGA). The analytical data of the complexes show the formation of 1:1 [M:L] ratio, where M represents Ni(II), Co(II) and Cu(II) ions, while L represents the deprotonated hydrazone ligand. IR spectra show that SAH is coordinated to the metal ions in a tridentate manner through phthalazine-N, azomethine-N and phenolic-oxygen groups. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria and fungi. Proton-ligand association constants of (SAH) and the stepwise stability constants of its metal complexes are determined potentiometrically in 0.1 M NaNO3 at different temperatures and the corresponding thermodynamic parameters were derived and discussed. The order of −ΔG° and −ΔH° were found to obey Mn2+ < Co2+ < Ni2+ < Cu2+, in accordance with the Irving–Williams order. The complexes were stabilized by enthalpy changes and the results suggest that the complexation is an enthalpy-driven process. The concentration distribution diagrams of the complexes are evaluated.

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► A new hydrazone ligand derived from the biologically active hydralazine was synthesised and characterized.
► Metal complexes were synthesised and characterized and showed promising biological activity.
► Stability and structural characterization of the complexes are supporting the biological activity of this class of complexes.
► Stability constant data is used to calculate the equilibrium distribution of the metal complexes in biological fluids.