Synthesis of new heterocyclic N'-(2-hydroxy-3-methoxybenzylidene)-4-oxopiperidine-1-carbohydrazide and its mononuclear metal (II) complexes: spectroscopic characterization, fluorescence, DFT, thermo-kinetic, and antimicrobial studies

Abstract

The new hydrazone Schiff base N'-(2-hydroxy-3-methoxybenzylidene)-4-oxopiperidine-1-carbohydrazide (H2L) was synthesized by the condensation reaction of 2-hydroxy-3-methoxybenzaldehyde (HMB) and 4-oxopiperidine-1-carbohydrazide (CPH). The new mononuclear complexes of type the [Mn(HL)(Cl)(H2O)2], [Co(HL)(Cl)(H2O)2], [Ni(HL)(Cl)(H2O)2], [Cu(HL)(Cl)(H2O)2] have been prepared and characterized by elemental, molar conductance, IR, electronic absorption, magnetic susceptibility, and thermal decomposition data. The identity and purity of synthesized hydrazone ligand (H2L) was confirmed by elemental analysis, IR, 1H and 13C NMR, and ESI-Mass spectroscopy. ESR studies of the Cu(II) complex revealed that hyperfine splitting parameters A|| =287cm-1 > A⊥=257cm-1 which indicates at electrons interact with only one copper nucleus with distorted octahedral geometry. Powder X-ray diffraction pattern of hydrazone ligand and its divalent complexes have been inferred from their nanocrystalline nature. The fluorochromes of the ligand and its metal (II) complexes emitted the fluorescence in the solid state with good resonation (0.2nm) spectra in the region of λ(527-545nm). DFT optimized structures of ligand and its metal complexes showed expected molecular structure with frontier molecular orbitals energy band gap (Δ𝐸) = 4.258 a.u. The simultaneous (TG-DTG) study of metal complexes was found more thermally stable due to the ‘structural complexity’ at high temperatures. The thermo-kinetic activation parameters viz., (Ea*), (∆S*), (∆H*), and (∆G*) of non-spontaneous decomposition have been evaluated from the Coat-Redfern equation, shows thermal stability order as Ni(II)

Keywords: Tridentate hydrazone, Metal complexes, Fluorescence emission, DFT, Thermo-kinetic study, Antimicrobial study