Synthesis, spectral characterization and biological evaluation of N′-(2-hydroxybenzylidene)benzohydrazide Schiff base and its ransition metal complexes

N′-(2-hydroxybenzylidene)benzohydrazide (HBAB) Schiff base and its transition metal complexes have attracted considerable attention because of their versatile coordination behavior and diverse biological applications. In the present study, HBAB and its Mn(II), Co(II), Ni(II), and Cu(II) complexes were synthesized and evaluated for antimicrobial, anticancer, antitubercular, haemolytic, antidiabetic, and molecular docking activities. Structural characterization was carried out using elemental analysis, UV–Visible, FT-IR, 1 HNMR spectroscopy, molar conductivity, magnetic susceptibility, and thermogravimetric analysis. Biological investigations were performed using agar diffusion, SRB cytotoxicity, haemolytic, α-amylase inhibition, microplate Alamar Blue, and molecular docking assays against EGFR and estrogen receptor proteins. The synthesized compounds were obtained in good yields (79–85%) and showed low molar conductance values (10.4–14.6 Ω −1 cm 2 mol −1 ), indicating their non-electrolytic nature. Spectral studies confirmed coordination through azomethine nitrogen and phenolic/carbonyl oxygen atoms. Magnetic moment and electronic spectral data suggested octahedral geometry for Mn(II), Co(II), and Ni(II) complexes, whereas the Cu(II) complex exhibited square-planar geometry with magnetic moment value of 1.64 BM. Thermogravimetric analysis confirmed the absence of coordinated water molecules also thermal stability of the metal complexes compared with the free ligand. Biological studies revealed enhanced activity of metal complexes relative to the ligand. Haemolytic analysis showed low erythrocyte toxicity with only 6–12% haemolysis at 500 μg/mL concentration. Cytotoxicity studies against MCF-7 and HT-29 cell lines demonstrated significant anticancer activity for Ni(II) and Cu(II) complexes with GI₅₀ values below 0.1 μM, comparable to Adriamycin. α-Amylase studies indicated concentration-dependent enzyme modulation, while Cu(II) and Ni(II) complexes exhibited comparatively higher activity at 1000 μg/mL concentration. Antimycobacterial screening against Mycobacterium tuberculosis H37Rv revealed that the Cu(II) complex possessed the highest activity with MIC value of 3.12 μg/mL. Molecular docking analysis demonstrated favorable binding affinities for the Cu(II) complex with docking scores of −10.31 and − 8.41 kcal/mol toward selected target proteins. Overall, metal coordination significantly enhanced the biological activity of HBAB, with the Cu(II) complex emerging as the most promising candidate for future therapeutic applications.