X-Ray Diffraction Studies on the Structures of Tetra- and Higherammine Complexes of Copper(II) Ion in Aqueous Solution

Abstract

Abstract From X-ray scattering measurements on ammoniacal aqueous solutions of copper(II) chloride at the NH3/Cu mole ratios of 4.8 and 5.0, four ammonia molecules at the equatorial position and other two water molecules at the axial one were found to be coordinated to a copper(II) ion at the distance of 2.03 and 2.33 Å, respectively. The radial distribution curve obtained for an aqueous solution of copper(II) chloride saturated with ammonia (NH3/Cu=11.2) showed that a higher ammine copper(II) complex than the tetraamminecopper(II) ion is formed in the solution. The complex has a distorted octahedral form in which the equatorial Cu–N bond distance is 1.93 Å. The axial apices of the octahedron at the distance of 2.30 Å are occupied by either an ammonia molecule and a water molecule or two ammonia molecules. The present study shows that the structures of the tetra- and higher-ammine copper(II) complexes in solution are different from those in crystal.