Synthesis, characterization, crystal structure and DNA binding studies of Pd(II) complexes containing thiosemicarbazone and triphenylphosphine/triphenylarsine

2-Oxo-1,2-dihydro-benzo[h]quinoline-3-carbaldehyde N-ethylthiosemicarbazone (H2L) and its palladium(II) metal complexes containing triphenylphosphine/triphenylarsine were synthesized and characterized. The structures of two new complexes [Pd(L)(PPh3)] (1) and [Pd(L)(AsPh3)] (2) were determined by single crystal X-ray diffraction. The Pd atom in both complexes is coordinated by the planar ligand and the P/As atom in square planar fashion, thus rendering the L-metal part of the molecules flat and suited for intercalation into DNA. The binding mode of the two new complexes to Calf thymus DNA was investigated by absorption spectroscopy, through the ethidium bromide (EB) displacement technique and viscosity measurements. These results indicate that the complexes bind to DNA via intercalation. Complex 2 shows stronger binding than that of complex 1 due to the deeper intercalation of the chromophore into the DNA because of the longer Pd–As versus the Pd–P distances in 2 and 1.