An unusual hydroxy-substituted mononuclear nickel(II) complex with a tetradentate Schiff base: Synthesis, spectroscopy, electrochemistry, crystallography, DNA binding, and theoretical investigation

Abstract

The 2:1 Schiff base condensates of 4-methyl-2,6-dibenzoylphenol (mdbpH) or 4-tert-butyl-2,6-dibenzoylphenol (bdbpH) with ethane-1,2-diamine, L1H2 and L2H2, respectively, were isolated and used to prepare nickel(II) derivatives. The resultant complexes, [Ni{OC6H2(CH3)(COC6H5)}2(C6H5CN(CH2)2NCC6H5)] (1) and [Ni{OC6H2(t-Bu)(COC6H5)}2(C6H5CN(CH2CHOH)NCC6H5)] (2), have been characterized by elemental analyses, conductivity measurements, mass spectrometry, IR, 1H and 13C NMR and electronic spectroscopy, cyclic voltammetry, and X-ray crystallography. The ligand precursors and complexes all crystallize in the P1¯ space group. In 1 and 2, the coordination at NiII, which shows a slight distortion from square planar towards tetrahedral geometry, comprises two phenolato O and two imine N atoms of the tetradentate (L2−) unit. Density Functional Theory (DFT) calculations provide a satisfactory description of the structural and electronic properties of the new compounds. Electrochemical studies of 1 and 2 are described. The interactions of complexes 1 and 2, and ligands L1H2 and L2H2, with calf thymus DNA were investigated by UV–Vis absorption titrations and cyclic voltammetric methods. Complexes 1 and 2, and ligands L1H2 and L2H2 bind to DNA via intercalation; the binding affinity of complex 1 is higher than that of complex 2 and of the ligand precursors L1H2 and L2H2.