The electronic properties and stereochemistry of the copper(II) ion. Part III. Some penta-ammine complexes

Abstract

The electronic, e.s.r., and i.r. spectra, and some magnetic moments of a number of stable penta-ammine complexes of the copper(II) ion are reported. The spectra are shown to be consistent with a square-based pyramidal configuration for the Cu(NH₃)₅²⁺ cation, but not consistent with a trigonal bipyramidal configuration. The three bands at 10,200, 13,200, and 16,800 cm.^–1 are assigned as the ²A₁â†�²B₁, ²B₂â†�²B₁ and ²Eâ†�²B₁ transitions respectively in C_4v symmetry. The Cu(NH₃)₅X₂ complexes (X = Br^–, I^–, ClO₄^–, BF₄^–) have face-centred cubic unit cells and isotropic e.s.r. spectra, suggesting that the Cu(NH₃)₅²⁺ cation in these complexes may be undergoing free rotation in the lattice at room temperature. In view of the existence of these complexes, with properties similar to those of the hexa-amminecopper(II) complexes, the latter are reformulated as Cu(NH₃)₅X₂,NH₃.