Synthesis, spectroscopic, CO-releasing ability, and anticancer activity studies of [Mn(CO)(3)(L-L)Br] complexes: Experimental and density functional theory studies

Two different series of manganese(I) tricarbonyl complexes containing phosphine-based (1-5) and 4'-substituted 2,2':6',2 ''-terpyridine-based ligands (6-10) have been synthesized in order to study their CO-releasing ability and to investigate their anticancer activity. All the synthesized complexes (1-10) have been fully characterized using standard spectroscopic and analytical techniques. Further 5, 7, and 9 have also been characterized by single-crystal X-ray diffraction studies. Although both the sets of ligands are pi-acceptors, they tend to change the Mn-CO bond strength upon complexation, thus affecting the CO release. Photoactivation of 1-5 and 6-10 has been achieved using 365 nm UV irradiation and low intensity visible light, respectively. The MnCO bond strength has been examined using the density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. In order to find the therapeutic viability of the visible light activated complexes, their cytotoxicity has been investigated both in the dark and under irradiation. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay reveals the potential application of some of the synthesized complexes especially towards the lung cancer cells in the dark condition.