Synthesis, structural insights, antimicrobial and cytotoxic potentials of Mn(II) and Fe(III) complexes with a novel Triazine–Quinoline ligand

Two novel Mn(II) and Fe(III) complexes were synthesized using a newly developed s -triazine ligand, N -(4,6- bis (3,5-dimethyl-1 H -pyrazol-1-yl)-1,3,5-triazin-2-yl)quinolin-8-amine, and their structures were fully confirmed using single-crystal X-ray diffraction. The Mn(II) ion is penta-coordinated with one NNN -tridentate chelate and two chloride ions leading to the [MnLCl 2 ] formula for 1 . The [Fe 2 L 2 ( μ -O)(H 2 O) 4 ](NO 3 ) 4 .3H 2 O comprised two hexacoordinated Fe(III) centers connected by an oxo bridge where each metal center is further coordinated with one NNN -tridentate chelate L and two water molecules. Hirshfeld analysis disclosed the highest contributing intermolecular interactions in the crystal of 1 to be H···H (43.3%), Cl···H (20.7%), and C···H (11.3%). For 2 , the main contributions are H···H (39.7 and 40.3%), O···H (33.6 and 32.0%), and H···C (16.0 and 15.9%), for units A and B , respectively. Atoms in molecules (AIM) analysis indicates that the Mn N, Fe N, and terminal Fe O bonds are predominantly closed-shell in nature, while modest covalent character is observed for the Mn Cl and bridging Fe O bonds. Moreover, 1 and 2 exhibited enhanced anticancer activities than the free ligand L against HCT-116 and A-549 cancer cell lines, where 2 being the most potent (IC 50 values of 9.05 ± 0.21 and 10.67 ± 0.25 μM, respectively). Compared to cis -platin, 1 and 2 demonstrated greater cytotoxic effects against HCT-116 cells (~1.2- and 3.1-fold, respectively). Additionally, the free ligand exhibited the strongest antimicrobial activity against B. subtilis and C. albicans with inhibition zone diameters (IZDs) of 18 and 11 mm, respectively, while 2 is more effective against P.vulgaris, with an IZD of 15 mm.