Solvation of copper(II) ions in liquid ammonia

X-ray absorption fine structure (XAFS) measurements have been performed at -50 degrees C on a 0.4 mol dm(-3) copper(II) nitrate solution in liquid ammonia. Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to determine the coordination number and bond distances for the solvated copper(II) ion in solution. The equatorial ammonia nitrogens are located 2.00 Angstrom from the copper and the axial nitrogen 2.19 Angstrom from the copper. However, it was not possible from the EXAFS analysis alone to conclude whether there was one or two axial nitrogens. Therefore? X-ray absorption near-edge structure (XANES) spectroscopy was combined with discrete variational X alpha (DV-X alpha) molecular orbital calculations for a series of five- and six-coordinated models to determine the coordination number and the geometry. The experimental XANES spectrum was best reproduced by a model where the copper(II) ion is pentacoordinated in liquid ammonia in a square pyramidal geometry with the copper(II) ion lifted above the average nitrogen plane.