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A series of some transition metal, Fe(III), Cu(II), Cd(II), and Hg(II), complexes with N′,2‐bis((Z)‐2‐oxoindolin‐3‐ylidene)hydrazine‐1 carbohydrazide (H3L) ligand have been synthesized, and their structures were elucidated based on their spectral analyses (Fourier transform infrared [FT‐IR], 1H nuclear magnetic resonance (NMR) and 13C NMR, UV‐visible (UV‐Vis), electron spin resonance (ESR), powder X‐ray diffraction [XRD], and mass spectroscopy), elemental analyses, conductance, and magnetic susceptibility measurements. The structures of the H3L ligand and its metal complexes were optimized using the DMol3 tool in the material studio package. The ligand behaves as binegative N2O3 pentadentate in [Fe(HL)(Cl)]·2H2O complex, mononegative N2O3 pentadentate in [Cu(H2L)(OAc)]·2H2O complex, mononegative N2O tridentate in [Cd(H2L)2]·H2O complex, and finally, neutral N2 bidentate in [Hg(H3L)(Cl)2]·2H2O complex. Coats–Redfern and Horowitz–Metzger methods were used to estimate the various thermodynamic and kinetic parameters. Cyclic voltammetry of the ligand in the absence and presence of Cd(II) and Hg(II) ions was studied. Fluorescence studies were performed in DMSO and showed that Cu(II) ions quench the fluorescence spectrum of the free ligand, whereas Cd(II) ions enhance it. The in vitro antimicrobial activities of the free ligand and its complexes against different bacterial strains and fungi Candida albicans were screened using agar‐disc diffusion techniques. The antioxidant potentials of the isolated compounds were also screened by employing SOD and ABTS free radical scavenging methods. Molecular docking studies were performed using Auto‐Dock tools to predict the best binding mode and predominant binding interactions.

Complexes of several transition metal ions with alpha-oximinoacetoacetyl pyridine-4-phenylthiosemicarbazone (H3OAPT) have been prepared. Attempts were made to elucidate their geometries by elemental analysis, molar conductance, magnetic measurements and by some spectroscopic (IR, ESR and electronic) techniques. All the investigated metal ions form mononuclear complexes except for CuII, which forms mononuclear and trinuclear complexes with its chloride and acetate salts, respectively. The IR spectra show that the ligand behaves as a mono or binegative tridentate. Moreover, it acts as a trinegative hexadentate in the trinuclear CuII complex. The protonation constants (logK1H = 9.9 and log K2H = 6.0), as well as the stability constants of the metal complexes, are determined by the pH-titration of H3OAPT and its metal(II) complexes against 0.01 M NaOH. CuII complexes possess square-planar stereochemistry while CoII and NiII have an octahedral one. The crystal field parameters of CoII and NiII complexes are evaluated.