Synthesis, structural, physico-chemical and biological properties of new palladium(II) complexes with 2,6-dimethyl-4-nitropyridine

Abstract

This paper describes the synthesis and properties of two new palladium(II) complexes with 2,6-dimethyl-4-nitro-pyridine (dmnp): mononuclear [Pd(dmnp) 2Cl 2] and dinuclear [Pd 2(dmnp) 2Cl 4]. Complexes were characterized on the basis of chemical and chromatographic analyses, MS and conductometric measurements, as well as by IR and NMR ( 1H and 13C) spectral studies. The crystal structures of ligand and mononuclear complex, trans-dichlorobis(2,6-dimethyl-4-nitro-pyridine)palladium(II), were determined by three-dimensional X-ray methods. The crystals of both compounds are monoclinic, space groups P2 1/ c with a=19.075(4), b=5.419(1), c=15.045(3) Å and β=108.15(3)° for (dmnp), and a=7.544(2), b=14.509(3), c=8.032(2) Å and β=90.32(3)° for [Pd(dmnp) 2Cl 2]. In the (dmnp) there are two crystallographically independent molecules in the unit cell. The nitro groups and methyl C atoms are coplanar with the ring plane. The hydrogen bond of the type C–H⋯O links the molecules into pairs around center of symmetry. These dimers are held together by contacts of the van der Waals type. In the crystal structure of [Pd(dmnp) 2Cl 2] the Pd atom lies on an inversion center and is four-coordinated by two pyridine N atoms and by two Cl atoms in trans positions. The coordination geometry is square-planar, with Pd–N and Pd–Cl distances of 2.033(2) and 2.311(1) Å, respectively. The two pyridine rings are mutually parallel, but they are twisted from the PdN2Cl2 coordination plane by about 88.5°. The preliminary assessments of anti-tumor properties of both complexes and ligand were evaluated as in vitro anti-proliferative activity in four human cancer cell lines: SW707 (adenocarcinoma of the rectum), T47D (breast cancer), HCV (bladder cancer) and A549 (non-small cell lung carcinoma). The [Pd(dmnp) 2Cl 2] exhibits strong cytotoxic activity against all cell lines whereas the free ligand and dinuclear [Pd 2(dmnp) 2Cl 4] are only moderate active.