Palladium(II) and platinum(II) complexes with thiourea derivatives and phosphine ligands: synthesis, characterization, DFT analysis, and biological evaluation

This study reports the synthesis and characterization of novel palladium(II) and platinum(II) complexes containing a thiourea-derived ligand (DCBIT) and various phosphine co-ligands. The ligand DCBIT was synthesized via a reflux reaction between benzimidazole and phenyl isothiocyanate. The ligand and its metal complexes were characterized using various spectroscopic techniques and elemental analyses. Spectroscopic data indicate that the thiourea-derived ligand coordinates to Pd(II) or Pt(II) ions through the imidazole nitrogen and thiocarbonyl sulfur atoms, acting as a bidentate donor. The phosphine ligands coordinate through the phosphorus atom, leading to square-planar geometries around the metal centers. The antimicrobial activities of the complexes were evaluated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), showing moderate to high antibacterial activity. In vitro cytotoxic activities of complexes [Pt(DCBIT)(Ph3P)Cl2], [Pt(DCBIT)(dppe)]Cl2, and [Pt(DCBIT)(dppf)]Cl2 were evaluated against CaCo-2 and MCF-7 cancer cells. Among these, [Pt(DCBIT)(dppf)]Cl₂ exhibited the highest cytotoxic activity, with an IC₅₀ value of 22.56 µg/mL against CaCo-2 cells. Computational studies provided valuable insights into the behavior of the ligands and their complexes. The results indicate that the free ligand, and dppe exhibits a wider energy gap, ΔE = (3.753 and 5.318 eV) making it more stable and less reactive than of Pt(II) complex (3.390 eV). KEY WORDS: Biological evaluation, DFT, Phosphine coordination, Pd(II) and Pt(II) complexes, Spectroscopic study, Thiourea derivatives ligands Bull. Chem. Soc. Ethiop. 2026, 40(4), 843-859. DOI: https://dx.doi.org/10.4314/bcse.v40i4.9