Dimethyltin(IV) Dichloride Derivatives of 4-N-Diethylaminosalicylaldimine Schiff Bases: Synthesis, Crystal Structures, Biological Activities, and Photophysical Properties

Abstract

Five new dimethyltin(IV) addition complexes with the general formula [SnMe₂Cl₂(HL^1–5)₂] (HSR 1–5) were synthesized via a 1:2 M reaction between dimethyltin(IV) dichloride and a series of 4-N-diethylaminosalicylaldimine Schiff bases. The ligands employed were HL¹ = 4-N-diethylaminosalicylidene-1-aminobenzene, HL² = 4-N-diethylaminosalicylidene-2-methyl-1-aminobenzene, HL³ = 4-N-diethylaminosalicylidene-3-methyl-1-aminobenzene, HL⁴ = 4-N-diethylaminosalicylidene-4-methyl-1-aminobenzene, and HL⁵ = 4-N-diethylaminosalicylidene-2,4,6-trimethyl-1-aminobenzene. The complexes were characterized by FT-IR, (¹H, ¹³C, and¹¹⁹Sn) NMR, HRMS spectroscopy and elemental analysis (C, H, N, Cl, and Sn). The molecular structures of HSR 1, HSR 2, HSR 4, and HSR 5 were elucidated by single-crystal X-ray diffraction. All these complexes feature a Sn(IV) center in a distorted octahedral geometry, where the six coordination sites are occupied by two trans chloride ions, two trans methyl groups, and two trans oxygen atoms derived from the Schiff base ligand. The structural analysis reveals that the tin atom exhibits an all-trans octahedral coordination geometry, with the two 4-N-diethylaminosalicylaldimine Schiff base ligands binding through their phenolic oxygen atoms as iminium–phenolato zwitterions. The complexes exhibited moderate antibacterial activity against all tested strains, including E. coli, P. aeruginosa, S. aureus, and S. pyogenes, with MIC values ≥ 200 μg/mL. Activity against the fungal strains C. albicans and A. niger was also assessed. DNA cleavage studies (agarose gel electrophoresis) exhibited that the complexes possess significant potency to cleave DNA. Their photophysical properties were also investigated, and UV–Vis absorption and fluorescence measurements provided insight into the electronic behavior of the complexes, with complex HSR 1 showing the highest fluorescence intensity.