Novel Mn2+, Fe3+, Co2+, Ni2+ and Cu2+complexes of potential OS donor thiosemicarbazide: Design, structural elucidation, anticorrosion potential study and antibacterial activity

Abstract Novel series of Co2+, Ni2+, Cu2+, Mn2+ and Fe3+complexes derived from 4,4-dimethyl-2,6-dioxo-N-phenylcyclohexanecarbothioamide (HDDPT) were prepared and characterized by conventional techniques. The complexes have adopted the formulae; {[Mn(DDPT)Cl(H2O)3]·3H2O, [Ni(DDPT-H)(H2O)(OH)], [Cu (HDDPT) Cl2(H2O)2]·2H2O, [Co(HDDPT)2Cl2] and [Fe (DDPT)Cl2], respectively. Spectral data revealed that HDDPT coordinates as OS donor in a neutral or mononegative manner. Electronic and magnetic measurements suggested a square planar geometry for Ni2+ complex and an octahedral one for the other complexes. X-ray powder diffraction data suggested monoclinic and orthorhombic structures for Fe3+ and Ni2+complexes, respectively. DFT method was utilized to prove the geometry and evaluate the bond lengths, bond angles as well as different energetic parameters. The thermal stability of the compounds was examined and the corresponding thermodynamic parameters were determined using Coats-Redfern and Horowitz-Metzger methods. Also, the corrosion hindrance of carbon steel (CS) in 0.5 M HCl by HDDPT was carried out using potentiodynamic polarization (PP) measurement. The data proved the thiosemicarbazide to be a powerful inhibitor and it is demonstrated that the protection efficiency and surface converge (Ɵ) increase with increasing the inhibitor concentration and decrease with increasing temperature. Finally, the adsorption procedure obeys Langmuir's adsorption isotherm. Moreover, all compounds were screened against the growth of four pathogenic bacterial strains.