Crystal structures, cyclic voltammetry and DNA binding of two mononuclear nickel(II) complexes

Two unsymmetrical complexes, [NiL¹]ClO₄ (1) and [NiL²]ClO₄ (2) have been synthesized and characterized by IR, UV, ES-MS and single crystal X-ray diffraction, where HL¹ and HL² are, respectively, the [1+1] condensation products of 2,6-diformyl-4-X-phenol (X = F or CH₃) with N ¹-(2-aminoethyl)-N ²-(4-nitrobenzyl) ethane-1,2-diamine. The coordination geometry of the metal in both complexes can be approximately described as square planar with a mean plane deviation of 0.032 Å in complex 1 and 0.027 Å in complex 2, respectively. The binding activities of the complexes toward calf-thymus DNA have been analyzed by spectroscopy and viscosity methods. The binding constants of 1 and 2 obtained from UV spectroscopic studies are 5.43 × 10⁵ and 1.83 × 10⁵ M^?1, respectively, while the linear Stern–Volmer quenching constants obtained from fluorescence spectroscopic studies are 0.83 × 10³ and 0.71 × 10³ M^?1, respectively. The cyclic voltammograms of the complexes show a pseudo-reversible electrochemical process.