New mono- and dinuclear complexes of 7-azaindole-3-carboxaldehyde with palladium(II): crystal structure, IR and Raman spectra, DFT calculations and in vitro antiproliferative activity

Abstract New Pd(II) complex, trans- [PdCl 2 (7AI3CAH) 2 ], containing 7-azaindole-3-carboxaldehyde (7AI3CAH) and the dinuclear complex [Pd 2 (7AI3CA) 4 ]·DMSO with the deprotonated ligand (7AI3CA) have been prepared and characterized by X-ray crystallography, infrared and Raman spectroscopy, DFT calculations and antiproliferative activity studies. A single crystal X-ray analysis of [Pd 2 (7AI3CA) 4 ]·DMSO has shown that the complex crystallizes in Cmca space group with the following unit cell dimensions: a  = 15.6593(9), b  = 17.9444(8), c  = 13.8915(7) A, V = 3903.5(3) A 3 , Z  = 4. Two ligands and DMSO solvate molecule are disordered. In this complex, the Pd 2 4+ unit is surrounded by four N -deprotonated 7AI3CA − anions with a Pd–Pd distance of 2.7122(12) A. Vibrational spectroscopic studies have revealed that in trans- [PdCl 2 (7AI3CAH) 2 ] complex, palladium(II) is bound to two pyridine nitrogen atoms of 7AI3CAH and to two chloride ions, in a square-planar trans arrangement. Comprehensive DFT calculations (including geometry optimizations, theoretical vibrational spectra and HOMO/LUMO orbitals) were performed for the four possible isomers of the dinuclear complex [Pd 2 (7AI3CA) 4 ] and for two isomers of [PdCl 2 (7AI3CAH) 2 ] using the B3LYP method with the 6–311++G(d,p)/LanL2DZ basis sets. The results have shown that the most stable isomers are: cis -(2,2)-[Pd 2 (7AI3CA) 4 ] for the dinuclear complex and trans -[PdCl 2 (7AI3CAH) 2 ] for the mononuclear complex. Detailed vibrational assignments of the experimental infrared and Raman spectra of both the palladium(II) complexes have been made on the basis of the calculated potential energy distributions (PEDs). The antiproliferative activity of trans -[PdCl 2 (7AI3CAH) 2 ] has been tested against the following human cancer cell lines: T47D and MCF7 (breast cancer), A549 (lung carcinoma), A2780 (ovarian cancer) and one normal cell line BALB/3T3 (mouse fibroblast). The trans -[PdCl 2 (7AI3CAH) 2 ] has revealed a remarkable cytotoxicity against the T47D tumour cell line (IC 50  = 4.77 ± 1.61 μM), which is over three-times higher than the clinically used cisplatin (IC 50  = 16.3 ± 3.9 μM). A study on stability of trans -[PdCl 2 (7AI3CAH) 2 ] in DMSO solution has been performed by FT-IR (ATR) spectroscopy.