Palladium(II) complexes containing seven halogeno-derivatives of 7-azaindole: molecular structures, vibrational spectra, DFT calculations and in vitro cytotoxic activity

Abstract

In the present work seven new complexes of Pd(II) containing halogeno-derivatives of 7-azaindole (7AIH), [PdCl2(L)2], where L = 3-chloro-7-azaindole (3Cl7AIH) or 3-bromo-7-azaindole (3Br7AIH) or 4-chloro-7-azaindole (4Cl7AIH) or 4-bromo-7-azaindole (4Br7AIH) or 5-bromo-7-azaindole (5Br7AIH) or 3-bromo-4-chloro-7-azaindole (3Br4Cl7AIH) or 5-bromo-3-chloro-7-azaindole (5Br3Cl7AIH) were prepared and studied by infrared and Raman spectroscopy accompanied by the DFT calculations. Full geometry optimizations and vibrational frequency calculations were performed for the two possible isomers cis and trans of [PdCl2(L)2] using the B3LYP method with the 6–311++G(d,p)/LanL2DZ basis sets. According to the theoretical results, the trans isomers are more stable than cis. As shown by the combined experimental and theoretical vibrational spectroscopic studies, only trans isomers with Ci symmetry are present, in the solid state. The combined experimental and theoretical studies have revealed that in [PdCl2(L)2] complexes, palladium(II) is bound to two pyridine nitrogen atoms of L ligands and to two chloride ions, in a square-planar trans arrangement. Detailed vibrational assignments of the experimental infrared and Raman spectra of these complexes have been made on the basis of the calculated potential energy distributions (PEDs). The antiproliferative activity of selected trans-[PdCl2(L)2] have been tested against human cancer cell lines (T47D, MCF7, A549 and A2780). The obtained IC50 values indicate that the title complexes possess lower cytotoxicity, in comparison to cisplatin.