Nickel(II) complex with an asymmetric tetradentate Schiff base ligand: synthesis, characterization, crystal structure, and DFT studies (original) (raw)
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Chemistry
In this study, a new bi-nuclear nickel complex [Ni2HL2(EtOH)2](Cl)(EtOH) of a Schiff base ligand, 2-[3-[2-hydroxybenzylideneamino]propyliminomethyl]phenol, was synthesized and characterized using UV/Vis, IR, HRMS, and TGA/DTA analysis. The molecular structure of the obtained complex was corroborated by the single crystal X-ray diffraction technique. It was found in the complex that two molecules of the ligand coordinate with two nickel atoms through azomethine-N and phenoxy-O, resulting in 6-coordinate distorted octahedral geometry, in which two ethanol molecules occupy the axial positions. The dielectric and electrical properties of the obtained samples were studied by impedance spectroscopy at different frequencies (from 1 Hz to 1 MHz) in the temperature range 298–343 K. It is found that the electrical conductivity of the Ni(II) complex is lower than that of the free ligand H2L, suggesting that the complexation traps the charge carriers contained in the ligand.
This article reports the synthesis and characterization of four Ni(II) Schiff base complexes, [Ni(L) (H2O)], where H2L = N-(dehydroacetic acid)-thiosemicarbazide (H2dha-tsc), N-(dehydroacetic acid)- 4-methyl-3-thiosemicarbazide (H2dha-mtsc), N-(dehydroacetic acid)-4-phenyl-3-thiosemicarbazide (H2dha-ptsc), or N-(dehydroacetic acid)-4-phenylsemicarbazide (H2dha-psc). The nature of bonding and stereochemistry of these complexes have been deduced from elemental analysis, infrared and electronic spectral studies, molar conductance, magnetic measurements, mass spectrometry, thermogravimetric analysis, 1H NMR and 13C NMR studies, and cyclic voltammetry. The stabilities of the complexes were determined in both solid state and solution. Molecular geometry optimizations and vibrational frequency calculations were performed with Gaussian 09 software package using density functional theory (DFT) with B3LYP/6-311G for a ligand (dha-ptscH2) and B3LYP/LANL2DZ combination for [Ni(dha-mtsc)(H2O)]. Based on the combined experimental and theoretical studies, square planar geometry has been proposed for the Ni(II) complexes. The Schiff base ligands and their metal complexes were screened for antibacterial activities against gram-negative bacteria (Escherichia coli ) at different concentrations to get their minimum inhibition concentration values. The bactericidal activity was enhanced in metal complexes as compared to free ligands.