<p>Synthesis of new Fe^+ 3, Co^+ 2, Cu^+ 2, Ru^+ 3, and Rh^+ 3 complexes of azo ligand; [5-((2-(3&#xa0;H-1 indol-3-yl) ethyl) diazenyl) quinolin-8-ol], of 1:2 (M: L) and characterized through various techniques. The complexes exhibited octahedral geometries. Thermogravimetric (TGA and DSC) analysis is utilized to study the thermal properties of various compounds and reveal the presence of coordinated water molecules in the complexes. The multi-stage thermal decomposition mechanisms, where the thermal breakdown is ended by the formation of metal oxide as the final stable residue. The antioxidant activity of the ligand and its metal complexes was evaluated using the DPPH free radical scavenging assay and Gallic acid as a standard substance. Among the tested compounds, the Ru complex exhibited the strongest activity, whereas the free ligand (HL) showed the weakest. Finally, the anticancer potential of the synthesized complexes was evaluated against selected breast cancer cell lines. Experiments were carried out using five different concentrations, and absorbance was recorded at 570&#xa0;nm to determine the mean percentage of cell viability. Results indicated that the highest tested concentration (524.70&#xa0;µg / Ml ) produced the greatest reduction in cancer cell growth. Among the tested compounds, the Ru complex demonstrated the strongest inhibitory effect, showing superior anticancer activity as well as the most pronounced ability to suppress free radical activity.</p> Graphical Abstract <p></p>