Synthesis, crystal structure and DNA binding studies of a binuclear copper(II) complex with phenanthroline

A new binuclear copper(II) complex, [Cu2Phen2Cl4] (Phen = 1,10-phenanthroline), has been synthesized and characterized. Single crystal X-ray diffraction results suggest that this complex structure belongs to monoclinic crystal system, Cc (no. 9) with the cell dimensions: a = 9.849(2) Å, b = 17.833(4) Å, c = 13.374(3) Å, β = 106.61(3)°, V = 2251.0(8) Å3, Dc = 1.8569 Mg m−3, F(000) = 1256.0, Z = 4. One Cu(II) central atom situated in a distorted square planar geometry is four-coordinated. The other situated in a distorted square pyramidal geometry is five-coordinated. Only one bridging Cl atom exists in the complex. Spectroscopic studies, including electronic absorption and fluorescence spectra, conductivity measurements and parallel factor analysis (PARAFAC) of fluorescence excitation–emission three-way data array, were carried out on the DNA binding behavior of the complex. All the results suggested that the breakage of DNA secondary structure took place at low molar ratio of complex to DNA (0.3 at most) and intercalation into the base pair of DNA took place at high molar ratio. Additionally, the equilibrium concentration of EB–DNA and EB (EB: ethidium bromide) could be directly obtained by PARAFAC algorithm, proved to be a convincing method for studying the interaction of complexes with DNA.