A multifaceted insight into dinuclear salicylatocopper(II) complexes containing 2,2'-bipyridine: Syntheses, structural characterization, spectral properties and biological activity.

The present study reports the syntheses, structural characterization, and biological evaluation of five dinuclear copper(II) complexes containing substituted salicylato ligands and 2,2'-bipyridine as a neutral N,N´-donor ligand: [Cu₂(bpy)2(3-F-Sal)2] (1), [Cu₂(bpy)2(4-Cl-Sal)2] (2), [Cu₂(bpy)2(3-Cl-Sal)2] (3), [Cu₂(bpy)2(4-MeO-Sal)2] (4), and [Cu₂(bpy)2(3,5-I-Sal)2] (5a). This work demonstrates that variations in preparation methods can lead to solid-state structural variability. Single-crystal XRD diffraction and complementary spectroscopic methods revealed a conserved CuN₂O₃ coordination environment, while substituent effects governed hydrogen bonding and secondary interactions demonstrated by Hirshfeld surface analyses. In DMSO solution, the complexes may display partial decomposition into mononuclear Cu(II) species, which appear to represent the solution-active form. DNA-binding studies combining electronic absorption titration, viscosity measurements, and ethidium bromide displacement indicated mixed binding mode, with halogenated derivatives exhibiting the highest affinity. The binding to bovine serum albumin resulted in moderately stable ground-state adducts. The antimicrobial evaluation showed negligible activity only for most compounds, whereas the iodinated salicylate complex achieved measurable inhibition of Staphylococcus aureus. Redox-based assays revealed substituent-dependent modulation of reactive oxygen species (ROS). The methoxy-substituted complex displayed the strongest superoxide dismutase (SOD) mimetic behaviour, while electron-withdrawing or bulky functional groups promoted increased ROS formation in a Fenton-like model system, consistent with electrochemical findings. Catecholase-like studies further highlighted pronounced differences in catalytic competence across the series of studied complexes. These results show that modest substituent variations in salicylatocopper(II)-bipyridine systems modulate their solution-phase speciation, redox behaviour, and interactions with biomolecules, thereby influencing their catalytic and ROS-related profiles under biologically relevant conditions.