Synthesis and Antibacterial Investigation of Triphenylphosphine-Stabilized Cobalt Schiff Base Complexes

Abstract

This study reports the preparation, characterisation and antibacterial activity of cobalt (II) Schiff base complexes (C1-C5) bearing triphenylphosphine (PPh3) as a co-ligand. Five Schiff base ligands (L1 to L5) were prepared by condensation of selected aldehydes and ketones with primary amines or hydrazines under acid catalysis in ethanol. The synthesised compounds were characterised by infrared (FTIR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy and magnetic susceptibility measurements. In vitro antibacterial screening was carried out using agar well diffusion method against Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa. FTIR analysis revealed coordination through the azomethine bond with characteristic bands at 1556 and 1684 cm⁻¹ with C–N ν (cm-1) between 1306 and 1338 cm⁻¹, and the C–P ν (cm-1) of the PPh3 observed between 1075 and 1088 cm⁻¹. The UV- Vis absorption peaks of 368, 342, 367 and 377 nm in complexes C1, C2, C3 and C5 respectively were assigned to respective Ligand to Metal Charge Transfer (LMCT). Magnetic susceptibility measurements revealed paramagnetic behaviour in C1, C4 and C5 with chi g values between 1.2 x10 -7 and 1.85x10-6, while C2, (-6.3 x10 -7) and C3 (-8 x10 -8) were diamagnetic. The antimicrobial results showed that the cobalt (II) complexes were substantially more active than their free-ligand against all four bacterial test organisms. The particularly notable anti-Pseudomonal activity in all five cobalt (II) complexes. The complexes displayed inhibition zone ranging from 20-29 mm, surpassing the standard drug Ofloxacin (23.50 mm) and showing significant enhancement over the free PPh3, ligands and cobalt salt.