Synthesis,spectral and structural investigations,theoretical studies,and antibacterial activity of 4-(2-hydroxynaphthalen-3-ylamino)pent-3-en-2-one and its diphenyltin(IV) complex

The Schiff base, 4-(2-hydroxynaphthalen-3-ylamino)pent-3-en-2-one (H₂L) and its diphenyltin complex have been synthesized and characterized by elemental analysis and FT-IR, ¹H, or ¹¹⁹Sn NMR spectroscopy. The structures of free ligand and complex have been confirmed by single-crystal X-ray diffraction. In the structure of H₂L, enolic proton is transferred to imine nitrogen and there is an intramolecular hydrogen bond between amine and carbonyl group. There are also 1-D intermolecular hydrogen-bonded chains with π–π stacking between chains. SnPh₂L is crystallized in the Pca2(1) orthorhombic space group with four molecules in an asymmetric unit cell. The geometry around tin is a highly distorted trigonal bipyramid with Schiff base completely deprotonated and coordinated tridentate to tin via phenolic and enolic oxygen atoms in axial and imine nitrogen in equatorial positions. The results of X-ray diffraction were also compared with density functional theory calculations. These calculations also confirm the keto-amine tautomeric form for Schiff base in solid phase. The in vitro antibacterial activities of ligand and complex have been evaluated against Gram-positive (Bacillus cereus and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. H₂L showed no activity but the diphenyltin(IV) complex exhibited good activities along with the standard antibacterial drugs.