Different spectroscopic approaches and thermal investigations were used to identify the structures of Fe (III), Co (II), Ni (II), Cu (II), Y (III), Zr (IV), La (III), and U (VI) complexes with Gat-o-phdn. The practical data confirm that Gat-o-phdn reacted with the metal ions as a tetradentate ligand through the two nitrogen atoms of azomethine groups and two oxygen atoms for caroboxylate groups forming distorted octahedral complexes. The kinetic characteristics of the complexes and thermal degradation phases were specified using the Coats–Redfern and Horowitz–Metzger procedures. The results of DFT calculations show that the computed and experimental geometrical parameters coincide quite well. For Cu (II) complex with smaller ΔE value (0.002 eV), it is more reactive, and for U (IV) complex with the higher ΔE value (0.051 eV), it is less reactive. According to antibacterial activity assays, the Cu (II) complex had strong activity against S. typhi, S. aureus, and B. cereus when compared with other complexes and high activity against S. typhi and S. aureus when compared with Gat-o-phdn. Also, the complexes of Fe (III), Co (II), Ni (II), Y (III), Zr (IV), La (III), U (VI), and Gat-o-phdn Schiff base are very highly significant against S. typhi, S. aureus, and B. cereus (P > 0.001)