Inert Low-Spin Rhenium(I) Tricarbonyl Complexes of Phosphine-Based Schiff Bases: Integrating Synthesis, Luminescence, Structural Elucidation, and Biological Activity

Abstract

Rhenium(I) tricarbonyl complexes in their monometallic forms have been extensively studied, mainly for their potent inhibitory activity against cancer cells. In this study, we report the synthesis, photoluminescence, crystal structure, and in vitro biological screening of five (5) ligands and their corresponding metal complexes. Of the five ligands, three crystal structures were analysed (with one being an oxidized ligand), while four metal complexes were studied. All crystallized in the monoclinic crystal system. The ligands and complexes, under the Beer-Lambert concentration range, displayed tuneable luminescent properties, with emission energies influenced by the electronic nature of the substituents on the backbone of the Schiff Base ligands. The in vitro cytotoxicity of selected compounds was tested against a panel of human cancer cell lines, including pancreatic (PANC-1, CFPAC-1), breast (MCF7, MDA-MB-231), and cervical (CaSki, HeLa) cancers. While most compounds showed moderate activity, complexes Re-2 and Re-3 exhibited interesting cytotoxicity against MCF7 and MDA-MB-231 cells, with IC50 values of 11.42 and 12.07 μM, respectively.