Structural, spectral, DFT, pH-metric and biological studies on Cr(III), Mn(II) and Fe(III) complexes of dithione heterocyclic thiosemicarbazide ligand

Cr(III), Mn(II) and Fe(III) complexes derived from the quadruple potential dithione heterocyclic thiosemicarbazide ligand (H2PET) have been prepared and characterized by conventional techniques. The isolated complexes were assigned the formulae, [Cr(HPET)(H2O)2Cl2]·3H2O, [Mn(HPET)(H2O)Cl]2 and [Fe(HPET)(H2O)2Cl2]·H2O, respectively. IR data revealed that the ligand behaves as monobasic bidentate through (CN)py and (CS) groups in both Cr(III) and Fe(III) complexes. In the binuclear Mn(II) complex, H2PET acts as NSNS monobasic tetradente via (CN)py, (CS), (CS) and the new azomethine, (NC)* groups. An octahedral geometry for all complexes was proposed. The bond lengths, bond angles, HOMO, LUMO and dipole moment have been calculated by DFT using materials studio program to confirm the geometry of H2PET and its metal complexes. The ligand association constant and the stability constants of its complexes in addition to the thermodynamic parameters were calculated from pH metrically at 298, 308 and 318°K in 50% dioxane–water mixture, respectively. Also, the kinetic and thermodynamic parameters for the different thermal degradation steps of the complexes were determined by Coats–Redfern and Horowitz–Metzger methods. Moreover, the anti-oxidant (using ABTS and DPPH methods), anti-hemolytic, and cytotoxic activities of the compounds have been tested.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Preparation of binuclear Cr3+, Mn2+ and Fe3+ complexes of the new thiosemicarbazide. ► Elemental analysis, spectral characterization of the ligand and complexes. ► pH-metric studies in 50% dioxane–water mixture at different temperatures. ► Thermal behavior of the solid metal complexes was studied using TGA technique. ► The compounds were screened for antioxidant activity and cytotoxicity.