Syntheses, structural characterization and evaluation of the anti-tubercular activity of copper (II) complexes containing 3-methoxysalicylaldehyde-4-methylthiosemicarbazone

• Copper (II) complexes having 3-methoxysalicylaldehyde-4-methylthiosemicarbazone were synthesized and characterized using spectral techniques like FT-IR, NMR, UV-Vis, ESR, TGA and VSM. • SC-XRD data of complex 2 showed a distorted square pyramidal geometry. • The anti-tubercular activity of all the complexes is 10 3 times better than standard drugs used while exhibiting low cytotoxicity. • Selectivity index value shows that complexes can be excellent anti-TB agents if treated in vivo. In the present work three novel copper (II) complexes ([CuL(CH 3 COO)] ( 1 ), [CuL(phen)] ( 2 ) and [CuL(bpy)] ( 3 ) (where phen=1,10-phenanthroline; bpy=2,2′ bipyridyl)) containing 3-methoxysalicylaldehyde-4-methylthiosemicarbazone ( HL ) were synthesised and characterised. All the complexes were characterized using spectral techniques like FT-IR, ESI-MS, TGA-DTA, UV–Vis, ESR and VSM. The structure of complex 2 was confirmed by single-crystal X-ray structure determination. Complex 2 crystallized in a monoclinic crystal system and P 2 1 /n space group with a distorted square pyramidal geometry. In vitro anti-TB and cytotoxicity studies were also carried out using MABA (Microplate Alamar Blue Assay) and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) assay, respectively. All the copper (II) complexes have shown excellent anti-TB properties in the nano-molar concentration range and exhibit low cytotoxicity.