Synthesis, structure, and DNA-binding studies of a new tetracopper(II) complex bridged by dissymmetrical N-benzoato-N′-(2-aminoethyl)oxamide

Abstract

A new oxamido-bridged tetracopper(II) complex, [Cu4(oxbe)2(bpy)2](ClO4)2 · 2H2O, where H3oxbe and bpy stand for N-benzoato-N′-(2-aminoethyl)oxamide and 2,2′-bipyridine, has been synthesized and characterized by elemental analyses, molar conductivity, infrared and electronic spectra, and single-crystal X-ray diffraction. It crystallizes in triclinic system, space group P-1, with crystallographic data: a = 7.829(5) Å, b = 12.680(5) Å, c = 13.420(5) Å, α = 104.665(5)°, β = 95.275(5)°, γ = 106.931(5)°, and Z = 1. The circular tetranuclear copper(II) cation [Cu4(oxbe)2(bpy)2]2+ with an embedded center of inversion is assembled by a pair of cis-oxbe-bridged dinuclear copper(II) units through coordination between carboxyl and copper(II). One copper(II) is located in a slightly distorted square-planar environment, while the other is in a distorted square-pyramidal geometry. In the crystal structure, abundant hydrogen bonds and aromatic stackings link the tetranuclear copper(II) units into an overall 3-D framework. Interactions of the tetranuclear copper(II) complex with herring sperm DNA (HS-DNA) are investigated by using UV absorption and fluorescence spectra, electrochemical techniques, and viscometry. The results suggest that the tetranuclear copper(II) complex interacts with DNA by intercalation with an intrinsic binding constant of 1.47 × 105 mol−1 L.