New derivatives of N₂O₂ tetradentate Schiff bases, from condensation of meso-1,2-diphenyl-1,2-ethylenediamine and salicylaldehyde derivatives (X-salicylaldehyde; X = 3-OMe, 4-OMe, 5-OMe, 6-OMe, 5-Cl, 5-Me), and oxidovanadium(IV) complexes were synthesized and characterized by ¹H NMR, UV-Vis, IR spectroscopy, and elemental analysis. Crystal structure of 5-OMe; H₂L³ and two of the complexes (VOL² and VOL³) were also obtained. In the crystals, the molecule of H₂L³ is C_i symmetrical, as it occupies the special position on the center of symmetry; its conformation is partially determined by classical intramolecular O–H···N hydrogen bonds. The complexes have monomeric structures with a distorted square pyramid of vanadium, with the oxo ligand in the apical position. Cyclic voltammetry studies show quasi-reversible V^IV/V^V redox for which the presence of electron-withdrawing groups on salicylaldehyde derivatives shifts the E° to more positive values. The complexes were used as catalysts for selective epoxidation of cyclooctene with tert-butylhydroperoxide as oxidant, in various solvents and reaction conditions. High catalytic activities and excellent selectivity was found. The catalytic activity of the complexes increased increasing E°, a consequence of the presence of electronegative substituents. This epoxidation process with the new catalysts was also studied under solvent-free condition and excellent reactivity was observed.

Generation of well-defined potential metallotherapeutics for cancer treatment, one of the most population-threatening diseases, is challenging and an active area of modern research in view of their unique properties and thus multiple possible pathways of action in cells. Specifically, Schiff base ligands were recognized as very promising building blocks for the construction of stable and active complexes of numerous geometries and topologies. Incorporation of Ag(I) ions allows for the formation of flat complexes with potential unoccupied coordination sites, thus giving rise to specific interactions between the metallotherapeutic and biomolecule of interest. Herein, we present the design, synthesis and characterization of new Schiff base ligand L and its Ag(I) bimetallic complex [Ag₂L₂]²⁺ with two planar moieties formed around the metal ions and connected through cyclohexane rings, confirmed by X-ray measurements. The compounds were described in context of their potential use as anticancer drugs through DNA and BSA binding pathways by several spectroscopic methods (CD, UV-Vis, fluorescence). We revealed that both, L and [Ag₂L₂]²⁺, interact with similar affinity with CT-DNA (K_b~10⁶ M⁻¹), while they differ in the type and strength of interactions with the model albumin–BSA. [Ag₂L₂]²⁺ binds BSA in both a dynamic and static manner with the K_sv = 8.8 × 10⁴ M⁻¹ in the Trp-134 and Trp-213 sites, whereas L interacts with BSA only dynamically (K_SV = 2.4 × 10⁴ M⁻¹). This found further confirmation in the CD studies which revealed a reduction in α-helix content in the albumin of 16% in presence of [Ag₂L₂]²⁺.