Conventional Liquid-State Synthesis of Glycine-Benzaldehyde Schiff Base Metal Complexes: Methodological Considerations and Antimicrobial Efficacy

Abstract

Despite growing interest in the emergent solid-state methods, conventional liquid-state reflux remains the main way to synthesize Schiff base transition metal complexes. This study describes a detailed framework for liquid-state synthesis, using the preparation of a glycine-benzaldehyde Schiff base ligand and its Fe(II), Co(II), and Cu(II) complexes as ingredient. The ligand was made by ethanolic reflux with methylamine as a catalyst, and the metal complexes were prepared in methanol at room temperature (30 °C) for 24 hours with a 2:1 ligand-to-metal ratio. The products were analyzed using FTIR, UV-Visible spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), magnetic susceptibility, and antimicrobial screening with agar well diffusion. The ligand was obtained in 88.2% yield and showed a clear azomethine ν(C=N) stretch at 1679.2 cm⁻¹. Complex yields followed the Irving-Williams order: Cu(II) (81.6%), Co(II) (76.5%), and Fe(II) (71.2%). FTIR confirmed bidentate N,O-coordination by shifts in the imine band. XRD showed that the Co(II) complex was highly crystalline (494–1247 Å), while the Fe(II) product was nearly amorphous (~53 Å). Magnetic measurements indicated spin-crossover behavior for Fe(II). TGA showed that Cu(II) and Co(II) decomposed gradually above 200 °C, but Fe(II) broke down rapidly near 400 °C. The Co(II) and Cu(II) complexes showed broad-spectrum antimicrobial activity against Staphylococcus aureus, Escherichia coli, Aspergillus niger, and Candida albicans at 100 µg/mL. Liquid-state synthesis offers clear benefits, such as thermodynamic control, improved crystallinity through Ostwald ripening, and access to spin-crossover materials. The framework described here can guide others using conventional solution-based synthesis in coordination and medicinal inorganic chemistry.