Abstract

The ligand (L1) of 2, 4-Dinitrophenylhydrazine and 3-Hydroxybenzaldehyde with N-(3-hydroxybenzaldehyde)-p-fluoroaniline ligand (L2) and their Fe(II) complex were prepared using grinding as a solvent-free synthetic method. The new compounds were characterized through melting point, solubility test, molar conductance, UV-Vis and IR spectrophotometry. Thermal stability of the ligands with their Fe(II) complex were studied by thermogravimetric analyses (TGA). Energy of activation (E_a), entropy of activation (ΔSo), free energy of activation (ΔG), enthalpy of activation (ΔHo) and collision frequency (Z) were calculated using Coats-Redfern’s approximation methods. Surface morphologies of the solid compounds were imaged by scanning electron microscopy (SEM). The particle sizes of the ligands and the metal complex were measured using a particle size analyzer at a diffraction angle of 10.9°. The newly synthesized compounds were screened for their antimicrobial activities. Melting points of the synthesized compounds were in the temperature range of 190 - 194℃ showing that they were fairly stable; solubility in non- polar solvents and molar conductance values (5.6 - 11.20 Ω/cm-2) indicates that the ligands and the complex are non-electrolytic in nature. The IR spectra showed bidentate ligands which coordinated through nitrogen atom of the azomethine and deprotonated oxygen atom of the hydroxyl group. The kinetic parameters revealed that the decomposition reactions of the synthesized compounds followed first order reaction and the activation energy (kJmol-1) were 54.05, 25.59 and 25.92 for HL1, L2and Fe(II) complex respectively. This revealed that HL1 required extra energy to form activated complex as compared to L2and Fe(II) complex. On the other hand, the collision frequencies were7.06 ×〖10〗^16, 4.01 ×〖10〗^4and 7.33 ×〖10〗^4s-1for HL1, L2and Fe(II) complex signifying extra spaces in HL1 thanL2and Fe(II) complex. Positive values of Gibb’s free energy (ΔG) of the synthesized compounds indicates that the decomposition was non-spontaneous, the positive values of ΔHo showed that enthalpy was the driving force for the decomposition of the synthesized compounds and were exothermic in nature. The antimicrobial studies revealed weak activity against the test bacteria and inactivity against the test fungi by the Schiff base ligands while their metal complexes significantly increased or induced antimicrobial sensitivity against the test microbes. Thus, the Schiff base complex hold promise as powerful and all-around antibacterial agent.