Alkyl chain length effect on construction of copper(II) complexes with tridentate Schiff base ligand and DNA interaction

Two tridentate Schiff base ligands were synthesized by condensation of equimolar amounts of benzoylacetone and 2-amino-1-ethanol or 3-amino-1-propanol, H₂L¹ and H₂L², respectively. The reaction of the Schiff base ligands with Cu(CH₃COO)₂ in methanol leads to (CuL¹)₄, 1 and (CuL²)₂, 2. In the tetranuclear cubane species, the tridentate H₂L has both a chelating and a bridging mode, after double deprotonation of the enolic OH groups. The copper(II) centers are five-coordinate with a NO₄ donor set from the ligands. The coordination geometry around each copper ion is essentially square pyramidal with one nitrogen and two oxygens from one ligand and two oxygens of adjacent ligands from the next unit of the cubane. In dinuclear 2, H₂L² has chelating and bridging modes after double deprotonation of the enolic OH groups. The dianionic form of the Schiff base coordinates forming a six-membered chelate ring with Cu(II). Two such monomeric CuL² entities are eventually linked through the alkoxo bridges to produce dinuclear 2. The absorption spectra strongly suggest that 2 interacts with CT-DNA. Both 1 and 2 appear to be more efficient than the parent compound in DNA cleavage.