Copper is also known to exist in the +3 oxidation state, which is believed to be involved in some biological electron-transfer reactions. (a) Would you expect this oxidation state of copper to be stable? Explain. (b) Name the compound \(\mathrm{K}_{3} \mathrm{CuF}_{6}\) and predict the geometry of the complex ion and its magnetic properties. (c) Most of the known Cu(III) compounds have square planar geometry. Are these compounds diamagnetic or paramagnetic?

The stability of an ion depends on its electron configuration. Copper, which is a transition metal, usually exists in the oxidation state of +1 or +2, due to loss of 1 or 2 electrons from the outer orbital. Given that copper's electron configuration is [Ar]3d10 4s1, losing 3 electrons from this configuration to form a Cu(III) ion would involve removing a more tightly held 3d electron. Such a process is energetically unfavorable, thus making Cu(III) unstable.

The compound \(K_3CuF_6\) is named Potassium Hexafluorocopper(III). This indicates that the copper ion in the compound is in the oxidation state +3. The geometry of the complex ion can be predicted using the VSEPR theory (valence shell electron pair repulsion) which postulates that the geometric arrangement of atoms, or groups of atoms, around a central atom in a molecule is determined principally by minimizing electron-pair repulsion. In this case, since the copper(III) ion is surrounded by six fluorine atoms, the complex ion will have an octahedral geometry. The magnetic property is determined by the number of unpaired electrons. In this case, since the Cu(III) ion is completely ionized, it loses all its 3d and 4s electrons. As such, no unpaired electrons are present, making it diamagnetic (it doesn't get attracted to a magnetic field).

In this case, the geometry of the complex is square planar, which suggests a dsp2 hybridization. If a copper(III) complex exists, it usually loses all of its 3d and 4s electrons, leaving no unpaired electrons in the Cu(III) cation. This means that these compounds would generally be expected to be diamagnetic, meaning they are not attracted to a magnetic field.