New Mn(II) Mefenamates Appended by Substituted Bipyridine Linkers: Structural, Thermal, Magnetic, and Biological Investigations

Two new manganese complexes of NSAID mefenamic acid (Hmef) with heterocyclic diimines, 4,4′-diethoxy 2,2′-bipyridine (DEB) and 4,4′-dimethyl 2,2′-bipyridine (DMB) were synthesized. DEB crystallised in triclinic Pī space group, exhibiting a 2-D network. MM1 crystallised in triclinic P1 space group, with mef^2- adopting monodentate and bidentate chelate modes to Mn, owing to its flexibility and DEB with bidentate chelation. The interplay of O─H···O, N─H···O, and C─H···O interactions stabilised the overall lattice of MM1. MM2 crystallized in triclinic Pī space group with mef^2- and DMB adopting diverse coordination modes to Mn and the π–π stacking and hydrogen bonding interactions gave rise to a parallel alignment of Mn units when extended along b axis. The thermalprofiles of MM1 and MM2 corroborated with the crystal structure, evidencing the loss of solvent between RT- 127 °C, followed by ligand decomposition. XPS analysis of MM1 and MM2 validated the presence of Mn in + 2 oxidationstate, thereby confirming ligand composition. The magnetic susceptibility values for MM1 and MM2 increased with decreasing temperature, suggesting paramagnetic nature of Mn(II) in both the compounds. Interestingly, MM1 and MM2 exhibited 15.67 ± 0.21 % and 19.17 ± 0.10 % cell viability, respectively, of HepG2 cancerous cells at 100 µg/mL and possessed DNA cleavage activity, indicating their role in  biomedical applications.