Synthesis, crystal structures and antimicrobial activities of 3-methyl and 3-bromo substituted benzo[b]thiophene based thiosemicarbazones

A series of thiosemicarbazones (TSCs) (L1–5) containing benzothiophen moiety were prepared via the reaction of 3-methyl/3-bromobenzo[b]thiophene-2-carboxaldehyde with appropriate thiosemicarbazides. The compounds were confirmed by elemental analysis, FT-IR, 1H NMR, MALDI-TOF and single crystal X-Ray diffraction techniques. The compounds exist in the E conformation with respect to the azomethine C = N double bond as confirmed by their C8/C9/N1/N2 torsion angles being 178.4(2)° (L1), – 175.2(5)/177.4(5)° (L2), 177.5(2)° (L3), 179.7(3)° (L4), and – 177.4(7)° (L5). These compounds were researched for their antibacterial activity against Gram-positive bacteria (E. faecalis and S. aureus), Gram-negative bacteria (E. coli, P. aeruginosa and S. marcescens) and antifungal activity against a yeast species C. albicans. The ligands possessed varying degrees of antimicrobial activity. Generally, the compounds demonstrated higher efficacy against gram-positive bacteria than gram-negative ones. The antifungal activity of the compounds against C. albicans was found to be lower in comparison to their activity against bacteria.