Synthesis, Characterization, Biological Activity and Nano-Structure Study of Isoxazole-Dithiocarbamate Complexes

A new series of transition metal dithiocarbamate complexes derived from 3-amino-5-methylisoxazole, [ML2] [M = Fe(II) (1), Ni(II) (2), Cu(II) (3), Pt(II) (4), Cd(II) (5), Hg(II) (6)] and [PhHgL]2 (7), were synthesized by one-pot reaction of the isoxazole amine with CS2 in the presence of KOH followed by treatment with the corresponding metal salts. The ligand scaffold incorporates the coordination versatility of the dithiocarbamate moiety and the established bioactive profile of the isoxazole pharmacophore. Characterization of the complexes was done by molar conductivity, FT-IR, 1H and 13C NMR spectroscopy, powder XRD, SEM and EDX analysis. The IR spectra confirmed the bidentate κ²-S,S′ coordination of the dithiocarbamate moiety via the characteristic v(C=S), ν(C–S), ν(C–N) and ν(C=N) bands, while NMR data supported the proposed structures with the CSS carbon appearing at δ 200.26–203.76 ppm. XRD analysis showed that the Fe and Pt complexes are mostly amorphous with short-range order, while the Cd and Ni complexes are semi-crystalline with nanoscale ordered domains of about 2.6–2.8 nm as estimated from the Debye–Scherrer equation. SEM images showed different morphologies which vary from plate-like, fibrous, granular, agglomerated and cauliflower-like microstructures. The particle size was in the nanometer range. EDX analysis confirmed the presence of the expected metal, sulfur, oxygen and carbon in all complexes. The antibacterial activity of complexes 1–4 against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) was investigated by the agar diffusion method. All the complexes show moderate activity, where the platinum complex [PtL₂] has the highest activity (16 mm against S. aureus and 19 mm against E. coli) and the nickel complex [NiL₂] has the lowest activity, although none of them reach the level of the standard antibiotic tetracycline (23 and 26 mm, respectively).