New homodi-and heterotrinuclear metal complexes of Schiff base compartmental ligand: interaction studies of copper complexes with calf thymus DNA

The new homodinuclear complexes 1–4 of the type LM^II ₂Cl₂], heterotrinuclear complexes 5 and 6 of the type LM^II ₂Sn^IVCl₆] where M = Cu^II, Mn^II, Co^II, Ni^II and Cu^II and Ni^II, respectively have been synthesized and characterized by elemental analysis and various spectroscopic techniques. The homodinuclear complexes possess two different environments (N₂ and N₂O₂donor sets) for holding the metal ions. The metal ion in N₂ set exhibits square planar geometry with two chloride ions in the inner sphere but rhombic structure is found in tetradentate N₂O₂ Schiff base cavity while in heterotrinuclear complexes Sn^IV atom is in the octahedral environment. The interaction of complexes 1 and 5 with calf thymus DNA was carried out by absorption spectroscopy and cyclic voltammetry. The intrinsic binding constants (K _b ) of complex 1 and 5 were determined as 3.2 × 10³ M⁻¹ and 9.6 × 10³ M⁻¹, respectively suggesting that complex 5 binds more strongly to CT-DNA than complex 1. Fluorescence studies along with viscosity measurements have also been checked to authenticate the binding of metal complexes with DNA.