An X-Ray Diffraction Study on the Structures of Bis- and Tris(ethylenediamine)copper(II) Complexes in Solution

Abstract The structure of copper(II) complexes with ethylenediamine (en) in solution has been determined by means of X-ray diffraction. The measurements were performed at 25 °C for aqueous ethylenediamine solutions of copper(II) nitrate, the mole ratio (en/Cu) in the solutions being 2.09 and 5.14. In the former solution the bis(ethylenediamine)copper(II) complex was contained as the main species, while the tris(ethylenediamine)copper(II) complex was predominantly formed in the latter solution. The analysis of the X-ray scattering data of the solutions showed that in the bis-complex four nitrogen atoms of the two ethylenediamine molecules coordinated to the central metal ion at the distance of 1.93 Å in a planar form and oxygen atoms of two water molecules were located at 2.92 Å above and below the plane. Since the axial Cu–OH2 bond distance is very long, the structure of the bis-complex can be regarded as square-planar. In the tris-complex the equatorial Cu–N bond length was 1.92 Å, which was practically the same as that within the bis-complex. The axial Cu–N distance was 2.22 Å.