The azo dye ligand 4‐(5‐chloro‐2‐hydroxyphenylazo)‐N‐thiazol‐2‐
ylbenzenesulfonamide (H2L) formed by the coupling reaction of sulfathiazole
and p‐chlorophenol was synthesized and characterized using elemental
analysis and Fourier transform infrared (FT‐IR) as well as UV–visible spectra.
Nano‐sized divalent Cu, Co, Ni, Mn and Zn complexes of the synthesized azo
dye ligand were prepared and investigated using various spectroscopic and
analytical techniques. Elemental and thermal analyses indicated the formation
of the Cu(II), Ni(II) and Mn(II) complexes in a molar ratio of 1:2 (L:M) while
Co(II) and Zn(II) complexes exhibited a 1:1 (M:L) ratio. FT‐IR spectral studies
confirmed the coordination of the ligand to the metal ions through the phenolic hydroxyl oxygen, azo nitrogen, sulfonamide oxygen and/or thiazole
nitrogen. The geometric arrangements around the central metal ions were
investigated applying UV–visible and electron spin resonance spectra, thermogravimetric analysis and molar conductance measurements. X‐ray diffraction
patterns revealed crystalline nature of H2L and amorphous nature of all synthesized complexes. Transmission electron microscopy images confirmed
nano‐sized particles and their homogeneous distribution over the complex
surface. Antibacterial, antifungal and antitumour activities of the investigated
complexes were screened compared with familiar standard drugs to confirm
their potential therapeutic applications. The Cu(II) complex showed IC50 of
3.47 μg ml−1 (5.53 μM) against hepatocellular carcinoma cells, which means
that it is a more potent anticancer drug compared with the standard cisplatin
(IC50 = 3.67 μg ml−1 (12.23 μM)). Furthermore, the Co(II), Ni(II), Cu(II) and
Zn(II) complexes displayed IC50 greater than that of an applied standard
anticancer agent (5‐flurouracil) towards breast carcinoma cells. Hence, these
complexes can be considered as promising anticancer drugs. The mode of
binding of the complexes with salmon serum DNA was determined through
electronic absorption titration and viscosity studies.