Synthesis, characterization and crystal structures of cobalt(III) and iron(III) complexes derived from bis-Schiff bases with antibacterial activity

Abstract

Schiff bases are versatile ligands for constructing transition metal complexes with diverse structural and biological properties. In this work, two brominated bis-Schiff bases, N,N′-bis(3-bromo-2-hydroxybenzylidene)ethane-1,2-diamine (H2La) and N,N′-bis(4-bromo-2-hydroxybenzylidene)ethane-1,2-diamine (H2Lb), were employed for the synthesis of five mononuclear Co(III) and Fe(III) complexes, namely [CoLa(N3)(DMF)] (1), [CoLa(NCS)(DMF)] (2), [CoClLb(OH2)]∙DMF (3), [FeLa(NCS)] (4), and [FeLb(NCS)(MeOH)] (5). The complexes were characterized by elemental analysis, infrared and electronic spectroscopy, molar conductivity measurements, and single crystal X-ray diffraction. Complexes 1–3 possessed six-coordinate octahedral Co(III) centers, in which the Schiff base occupied the equatorial coordination framework and azido, thiocyanato or chlorido/aqua ligands completed the coordination sphere. In contrast, complex 4 adopted a distorted square pyramidal Fe(III) geometry, whereas 5 exhibited a distorted octahedral Fe(III) coordination environment. The antibacterial activities of the ligands and complexes were evaluated against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens. Complex 3 gave the lowest MICs against B. subtilis, S. aureus and P. fluorescens (1.2, 2.3 and 37.5 μM, respectively), and shared the MIC of 18.8 μM against E. coli with 1 and 2.