Characterization and thermal studies of nano‐synthesized Mn(II), Co(II), Ni(II) and Cu(II) complexes with adipohydrazone ligand as new promising antimicrobial and antitumor agents

New seven complexes of N₁,N₆‐bis((2‐hydroxynaphthalin‐1‐yl)methinyl))adipohydrazone (H₂L) with MnCl₂?4H₂O, CoCl₂?6H₂O, NiCl₂?6H₂O, CuCl₂?2H₂O, Cu(NO₃)₂?3H₂O, CuSO₄?5H₂O, and Cu(OAc)₂?2H₂O have been prepared and characterized by the aid of elemental and thermal analyses, spectra (FT‐IR, ¹H NMR, MS, UV‐Vis, ESR, X‐ray powder diffraction), molar conductance and magnetic moment measurements. The XRD results unambiguously confirmed the nano‐sized particles of the complexes. The results showed that H₂L behaves as dibasic tetra‐dentate ligand towards the metal ions of interest. The low molar conductance values revealed the non‐electrolytic nature for the chelates. The magnetic moment data, UV‐Vis and ESR spectra denoted the formation of octahedral geometries for Mn(II) and Ni(II) complexes, whereas Co(II), Cu(II) complexes exhibited tetrahedral arrangement. The activation parameters for the thermal decomposition stages were calculated from TGA curves using Coats‐Redfern and Horowitz–Metzger methods. The obtained data were confirmed by 3‐D molecular modeling of the ligand and some complexes. The investigated compounds were screened for their antimicrobial activities against different types of organisms and antitumor activities towards human liver Carcinoma (HEPG2) cell to access their potential chemotherapeutic use. The free ligand (H₂L) exhibited a weak inhibition of cell viability with IC₅₀ of 11.80 μg/ml, complexes 4 , 6 and 7 showed a moderate activity with IC₅₀ of 5.56, 7.71 and 5.67 μg/ml, whereas complexes 1 , 2 , 3 , and 5 displayed a strong anticancer activity with IC₅₀ of 4.65, 3.97, 3.30 and 4.84 μg/ml, compared with IC₅₀ value of 4.73 μg/ml for the doxorubicin (standard cytotoxin drug).