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 P2(1)/h. with a = 11.671(1), b = 10.405(1), c = 13.124(1), beta = 115.60(1)degrees and Z = 4; [Pd(2Bz4M)Cl] (2) in the monoclinic space group P2(1)/c with a = 9.695(1), b = 15.044(1), c = 10.718(1) Angstrom, beta = 105.38(1)degrees and Z = 4 and [Pd(2Bz4Ph)Cl] (3) in the triclinic space group P (1) over bar with a = 9.389(1), b = 13.629(1), c = 15.218(1) Angstrom, alpha = 70.25(1), beta = 73.46(1), gamma = 83.57(1)degrees 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 GI(50) and LC50 than the complexes, H2Bz4Ph being the most active with GI(50) < 0.003 muM; LC50 = 13.4 muM; GI(50) = 9.3 muM, LC50 = 12.9 muM; GI(50) < 0.003, LC50 = 13.8 muM in the MCF-7, TK-10 and UACC-62 cell lines, respectively. Among the complexes, [Pd(2Bz4Ph)Cl] (3) exhibited the lowest values of GI(50) in the three studied cell lines. (C) 2004 Elsevier Inc. All rights reserved.