Palladium(II) complexes of 2-benzoylpyridine-derived thiosemicarbazones: spectral characterization, structural studies and cytotoxic activity

Palladium(II) complexes of 2-benzoylpyridine thiosemicarbazone (H2Bz4DH) and its N(4)-methyl (H2Bz4M) and N(4)-phenyl (H2Bz4Ph) derivatives were obtained and fully characterized. [Pd(2Bz4DH)Cl] (1) crystallizes in the monoclinic space group P21/c with a = 11.671(1), b = 10.405(1), c = 13.124(1), β = 115.60(1)° and Z = 4; [Pd(2Bz4M)Cl] (2) in the monoclinic space group P21/c with a = 9.695(1), b = 15.044(1), c = 10.718(1) Å, β = 105.38(1)° and Z = 4 and [Pd(2Bz4Ph)Cl] (3) in the triclinic space group P1¯ with a = 9.389(1), b = 13.629(1), c = 15.218(1) Å, α = 70.25(1), β = 73.46(1), γ = 83.57(1)° and two independent molecules per asymmetric unit (Z = 4). All complexes show a quite similar planar fourfold environment around palladium(II). A negatively charged organic molecule acts as a tridentate ligand and binds to the metal through the pyridine nitrogen, the imine nitrogen and the sulfur atom. A chloride ion occupies the fourth coordination site. The planar complexes stack nearly parallel to one another in the lattice conforming a layered crystal structure. The cytotoxic activity of the thiosemicarbazones and their metal complexes was tested against the MCF-7, TK-10 and UACC-62 human tumor cell lines. The ligands exhibit lower values of GI50 and LC50 than the complexes, H2Bz4Ph being the most active with GI50 < 0.003 μM; LC50 = 13.4 μM; GI50 = 9.3 μM, LC50 = 12.9 μM; GI50 < 0.003, LC50 = 13.8 μM in the MCF-7, TK-10 and UACC-62 cell lines, respectively. Among the complexes, [Pd(2Bz4Ph)Cl] (3) exhibited the lowest values of GI50 in the three studied cell lines.