Spectra-structure correlation based study of complex molecules of 1-isonicotinoyl-3-thiosemicarbazide with Ni2+, Mn2+ and Fe3+ using Raman, UV–visible and DFT techniques

• 1-isonicotinoyl-3-thiosemicarbazide (Hintsc) and its complexes with Ni2+, Mn2+, Fe3+ metal ions have been synthesized.
• A Spectra-structure correlation based study has been carried out to probe the molecular structure of complexes.
• Coordination property of metal ions with Hintsc is investigated using Raman spectroscopic, UV–visible and DFT methods.
• The three metals ions Ni2+, Mn2+ and Fe3+ exhibited octahedral coordination property with Hintsc.
• The molecular level properties viz. geometry optimization, MEPS and FMO plots have been studied by DFT method.

In present work, we have analysed the structural property of newly synthesized ligand and its coordination complex molecules with Ni2+, Mn2+ and Fe3+. The spectroscopic techniques UV–visible, IR, Raman and DFT methods are used. The newly synthesized ligand 1-isonicotinoyl-3-thiosemicarbazide (Hintsc) has supramolecular architecture stabilized through various intermolecular interactions viz. NH⋯O, CH⋯O, CH⋯N, NH⋯S and CH⋯S type hydrogen bonds as observed in the single crystal of the ligand. The single crystals of the complexes could not be obtained with high degree of homogeneity from the solutions therefore plausible geometry of the complexes have been proposed on the basis of Raman spectroscopy, UV–visible and DFT methods and coordination properties of Ni2+, Mn2+ and Fe3+ with ligand (Hintsc). The ligand Hintsc contains the thiosemicarbazide (TSC) moiety through which Ni2+, Mn2+ and Fe3+ metals are coordinated. Raman spectroscopy is used to investigate the binding of Ni2+, Mn2+ and Fe3+ with ligand (Hintsc). In Raman spectra, the disappearance of NH bending/ NH stretching and lower wavenumber region Raman spectra clearly confirms that Ni2+ and Mn2+ metals are coordinated through N3 and O sites of thiosemicarbazide (TSC) and consequently formed the chelate ring {C6N2N3MO}, where M Ni2+ and Mn2+. In Fe complex, Fe3+ is coordinated through N2 and S sites of TSC and formed the chelate ring {C7N3N2FeS}. The structural and molecular property of 1-isonicotinoyl-3-thiosemicarbazide (Hintsc) and its complexes with transition metals Ni2+, Mn2+, Fe3+ have also been studied by DFT technique. By means of UV–visible, Raman spectroscopy and DFT technique, it is found that Ni2+, Mn2+ and Fe3+ exhibit the octahedral coordination property with 1-isonicotinoyl-3-thiosemicarbazide (Hintsc).

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