Novel series of Zn^2+, Cd²⁺and Hg²⁺ complexes derived from (E)-2-((3-cyano-4,6-dimethylpyridin-2-yl)thio)-N'-(thiophen-2-ylmethylene)acetohydrazide (HDMAH) in1:1 or 2:1 (L:M) ratio. The complexes were characterized by conventional techniques adopting the molecular formulae; [Zn(HDMAH)₂Cl(OH)], [Cd(HDMAH)Cl₂H₂OEtOH]and[Hg(HDMAH)Cl(OH)EtOH]3EtOH, respectively. Electronic and infrared spectral dataconfirmed the coordination of HDMAH as   neutral ON bidentate in an octahedral environment around metal ion. The structure of Zn⁺² was also studied by XRD technique. was completed using the DFT method, which was also utilised to assess other energy properties include electronegativity, HOMO, LUMO, and hardness. As well as using TGA and DrTGA to evaluate thermal stability, Coats-Redfern and Horowitz-Metzger techniques were employed to determine the corresponding thermodynamic parameters of activation. Additionally, each molecule was examined for antioxidant using ABTS⁺ free radical scavenger and antihemolytic activities. The biological assay is extended to test the inhibition activity of breast cancer. The results revealed Zn⁺² possesses a potent activity among all title compounds