Abstract
The research demonstrates that thioether-based coordination complexes obtain their physicochemical properties and biological activity from both the metal ion type and the ligand molecular structure. The synthesized complexes showed tetrahedral coordination geometries, as evidenced by spectroscopic, magnetic, and conductivity measurements, which demonstrated that sulfur atoms function as the main donor sites. The behavior follows the soft donor–soft acceptor interaction framework, which allows the creation of stable metal–sulfur chemical bonds. The biological properties of metal coordination compounds produced better antibacterial effects than the unbound ligands. The improved results stem from two factors: enhanced lipophilicity after chelation, which enables better cell membrane penetration by bacteria, and decreased metal ion polarity due to electron delocalization within the chelate ring structure. The complexes become more accessible to the cell through these combined effects. The Ni(II) complex derived from ligand L1 exhibited the most effective antibacterial activity against both bacterial species. The d⁸ electronic configuration of Ni(II) leads to enhanced activity because it produces the best possible match between structural stability and electronic flexibility when the metal center binds to a tetrahedral coordination site. The compound shows better biological performance because its L1 structure contains a short ethylene bond, which produces a compact molecular arrangement that improves metal-sulfur bonding through its optimized metal-ligand electronic interactions. The research shows that thioether metal complexes exhibit antibacterial properties because their electronic structure interacts with their coordination and ligand structures in a combined manner, leading to the development of biologically active metal-based compounds.