Structural studies and cytotoxic activity of a new dinuclear coordination compound of palladium(II)-2,2:6,2-terpyridine with rigid dianionic 1,2,4-triazole-3-sulfonate linker

A new dinuclear coordination compound of palladium(II), [Pd-2(terpy)(2)(-tas-N-1,N-4)]SO(4)11H(2)O (1), was synthesized by tethering a doubly deprotonated 1,2,4-triazole-3-sulfonate (tas) linker generated in situ via oxidation of 1,2,4-triazole-3-thione (tat) under the synthetic conditions. X-ray diffraction analysis reveals that tat molecules adopt the thione form in the solid state, and are combined in infinite chains by symmetrically related classical intermolecular hydrogen bonds N1H1S1, N3H3N2 to give rise to R-2(2)(7) pattern in one-dimensional chains along the b-axis propagating along the a-axis. Further short contacts through lone pairs of N2S1 on the rings between the adjacent chains along the a-axis lead to a two-dimensional network structure. Compound 1 was characterized using infrared, H-1 NMR and UV-visible spectroscopies, electrospray ionization mass spectrometry and X-ray crystallography. The crystal structure determination of 1 reveals that the Pd(II) ions are coordinated with four nitrogen atoms: three from terpy and one from tas acting as an end-to-end (-1,4) bridging ligand. The Pd(II) ions in 1 adopt a distorted square planar geometry. The anti-growth effect of 1 was tested on colorectal cancer (HCT-15), non-small-cell lung cancer (A549), prostate cancer (PC-3) and cervical cancer (HeLa) cell lines using sulforhodamine B viability assay. The cytotoxic effect was further confirmed using adenosine triphosphate viability assay. Compound 1 shows a promising cytotoxic activity in the diverse cancer cell models in vitro (p <0.0001).