SYNTHESIS, CHARACTERIZATION AND NEMATOCIDAL STUDIES OF IRON (II) SCHIFF BASE COMPLEX OF 4 - HYDROXYBENZALDEHYDE AND O - PHENYLENE DIAMINE

Schiff base ligand was synthesised using solvent-free grinding method by condensing 4-hydroxybenzaldehyde (1.2214 g, 0.01 mol) with o-phenylenediamine (0.5407 g, 0.005 mol) in a 2:1 molar ratio, yielding a pale-yellow product with an 81.15% yield. Subsequent coordination with FeCl₂ (0.2028 g, 0.0016 mol) produced an Fe (II) complex with a yellowish-brown coloration and an improved yield of 85.91%. Physical characterization showed a decrease in pH from 6.69 ± 0.02 (ligand) to 4.93 ± 0.1 (complex), and an increase in electrical conductivity from 0.17 ± 0.01 µS/cm to 0.39 ± 0.2 µS/cm. The melting point also increased from 83.5 °C (ligand) to 103 °C (complex), indicating enhanced thermal stability. Solubility tests revealed both compounds to be soluble in ethanol, methanol, acetone, DMSO, and diethyl ether, but with limited solubility in water. FT-IR analysis confirmed coordination via the azomethine nitrogen and phenolic oxygen, as evidenced by the shift of the C=N stretching band from 1610 cm⁻¹ (ligand) to 1498 cm⁻¹ (complex), and appearance of new M–O or M–N bands around 600–500 cm⁻¹. UV-Visible spectra of the ligand showed peaks at 270 nm (π→π*) and 408 nm (n→π*), while the Fe (II) complex exhibited a new peak at 308 nm (LMCT) and a broad band near 500 nm (d–d transition). TGA analysis indicated initial decomposition of the ligand at ~150 °C and the complex at ~200 °C, confirming higher thermal stability of the metal complex. Nematocidal assays demonstrated enhanced biological activity of the Fe (II) complex across all tested concentrations (2.5–12.5 mg/mL), with mortality values reaching up to 12.5 at 12.5 mg/mL, compared to 4.0 for the free ligand and 10.0 for iron alone. The improved activity of the complex is attributed to increased lipophilicity and better membrane interaction. These results validate the successful synthesis of a thermally stable and biologically active Fe (II) Schiff base complex with potential applications in nematode control