The coordination chemistry of the copper(II), zinc(II) and cadmium(II) ions in liquid and aqueous ammonia solution, and the crystal structures of hexaamminecopper(II) perchlorate and chloride, and hexaamminecadmium(II)chloride

The coordination chemistry of the ammonia solvated copper(II), zinc(II) and cadmium(II) ions has been studied in liquid and aqueous ammonia by means of EXAFS spectroscopy, and in the solid state by means of crystallography and EXAFS spectroscopy. The ammonia solvated copper(II) ion is six-coordinated in Jahn-Teller distorted octahedral configuration with Cu-N bond distances of 2.050(5), 2.060(5) and 2.064(7) Å in the equatorial plane, and of 2.31(2), 2.31(2) and 2.34(2) Å in the axial positions in solid [Cu(NH3)6](ClO4)2, [Cu(NH3)6]Cl2 and [Cu(NH3)6]Br2, respectively, as determined by EXAFS. Solid [Cu(NH3)6](ClO4)2 crystallizes in a cubic space group, Fm3m, which does not allow a Jahn-Teller distorted configuration, and the crystallographic result is instead six equidistant Cu-N bonds at 2.091(13) Å. Solid [Cu(NH3)6]Cl2 crystallizes in a tetragonal space group, I4/mmm, with Cu-N bond distances of 2.068(7) and 2.24(2) in the equatorial and axial positions, respectively. The ammonia solvated copper(II) ion is also six-coordinated in Jahn-Teller distorted octahedral configuration in liquid and aqueous ammonia with Cu-N bond distances of 2.065(5) and 2.051(5) Å in the equatorial plane, and of 2.29(2) and 2.29(2) Å in the axial positions, respectively, as determined by EXAFS. The ammonia solvated zinc(II) ion is four-coordinated in tetrahedral configuration with mean Zn-N bond distances of 2.040(5) and 2.028(7) Å in solid [Zn(NH3)4](ClO4)2 and aqueous ammonia solution, respectively, while the zinc(II) ion seems to be five-coordinated in liquid ammonia with a mean Zn-N bond distance of 2.117(7) Å, as determined by EXAFS. The ammonia solvated cadmium(II) ion is six-coordinated in octahedral configuration with mean Cd-N bond distances of 2.346(7), 2.350(7) and 2.347(7) Å in solid [Cd(NH3)6]Cl2, liquid ammonia and aqueous ammonia solution, respectively, as determined by EXAFS. Solid [Cd(NH3)6]Cl2 crystallizes in a cubic space group with six equidistant Cd-N bonds at 2.341(4) Å in a regular octahedron.