Synthesis of Pd(II) and Ag(I) complexes with pyrazole thiosemicarbazone: Characterization of the molecular structure by DFT/X-ray diffraction, in vitro antibacterial activity and molecular docking study

New Pd(II) and Ag(I) complexes derived from (2E)-2-[(1,3-diphenyl-1H-pyrazol-4-yl)methylidene]-N-ethylhydrazine-1-carbothioamide (L) were synthesized. The compounds, with general formulas [PdL2]Cl2 and [AgL (phen)]NO3, 1,10-phenanthroline (phen), were characterized by physicochemical and theoretical techniques. Thus, the results obtained by IR, Raman, UV-Vis, NMR, and mass spectrometry data allowed the determination of the structures of complexes synthesized, indicating the chelation of ligand to the metals occurs through the sulfur atoms of thiol and the nitrogen of the azomethine group. Single-crystal X-ray diffraction (XRD) analysis revealed the formation of the E-isomer of the ligand. These results were confirmed with DFT calculations, in which atomic charge and molecular orbital analyses were conducted to predict the reactivity and stability of the compounds. The in vitro antibacterial assays were performed against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. With the Ag(I) complex exhibiting the best activity (MIC = 35.74 mu M) against S. aureus, this being attributed to a synergistic effect between the Ag(I) ion, the pyrazole-derived thiosemicarbazone ligand and the 1,10-phenanthroline coligand. Finally, the in silico molecular docking studies showed that all the compounds have a potential antibacterial effect, especially the complex [PdL2]Cl2 with a more negative scoring energy value indicating a stronger interaction between the macromolecules and the ligand.