Synthesis of a new pyridinyl thiazole ligand with hydrazone moiety and its cobalt(III) complex: X-ray crystallography, in vitro evaluation of antibacterial activity

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The present work report the synthesis, structural characterization and in vitro antibacterial studies of (4-(4-methoxy phenyl)-2-(2-(1-pyridine-2-yl)ethylidene)hydrazinyl)thiazole bromide (HL·Br) and its cobalt(III) complex, [CoL2]ClO4. HL⋅Br crystallizes in a space group Pbca in a nearly planar structure and the crystal structure of complex shows a CoIIIN6 coordination geometry in which each L shows N,N,N-donor binding modes. Solution magnetic susceptibility measurement of [CoL2]ClO4 by modified Evan’s method confirms the low spin diamagnetic nature of the cobalt(III) complex. New compounds were screened for their antibacterial studies against gram positive bacteria including Staphylococcus aureus, Streptococcus faecalis and Bacillus subtilis and gram-negative bacteria including Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Klebsiella pneumonia and Proteus vulgaris. Both the compounds show very stronger growth inhibition activity against gram negative bacteria than gram positive bacteria. Present study shows that HL⋅Br has maximum antibacterial activity against E. coli (25±0.2mm) and S. typhi (28±0.7mm) at an MIC of 200µg/mL and 50µg/mL respectively, showing greater MIC values than the standard antibiotic ciprofloxacin (8µg/mL against E. coli and 10µg/mL against S. typhi).