Question

Copper is 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 and magnetic properties of the complex ion. (c) Most of the known Cu(III) compounds have square planar geometry. Are these compounds diamagnetic or paramagnetic?

Short answer

(a) Unstable. (b) Potassium hexafluorocuprate(III); square planar; diamagnetic. (c) Diamagnetic.

Step-by-step solution

Understanding Copper's Oxidation States

Copper commonly exhibits +1 and +2 oxidation states, with +2 being more stable due to its electron configuration. The +3 oxidation state is less common and not very stable because it requires more energy to remove the third electron from copper.

Stability of Cu(III)

Since copper in the +3 oxidation state is rarely observed and involves removing an already stable electron from the +2 state, it is generally unstable. External factors may stabilize it temporarily in biological systems.

Compound Name

The compound \( \mathrm{K}_{3} \mathrm{CuF}_{6} \) is named Potassium hexafluorocuprate(III). This name reflects the presence of three potassium ions and a complex ion containing copper and fluorine.

Predicting Geometry of Cu(III) Complex

Cu(III) complexes commonly adopt a square planar geometry. The d-orbital splitting in this geometry, especially in 3d elements like copper, generally favors such a configuration due to better electron pairing energy.

Magnetic Properties of Cu(III)

Square planar Cu(III) compounds are usually low spin and can be diamagnetic due to paired electrons in the d-orbitals.

Analyze Most Known Cu(III) Compounds

Given their low-spin state and square planar configuration, most known Cu(III) compounds are diamagnetic, as their electrons are paired.

Key concepts

Biological Electron-Transfer

In biological systems, electron-transfer reactions play a key role in processes such as cellular respiration and photosynthesis. Copper can participate in these reactions, although its +3 oxidation state is rare and generally unstable. This instability arises because copper typically exists in +1 or +2 states, with the +2 state being more energetically favorable due to a stable electron configuration. In biological systems, however, external factors like specific protein environments can temporarily stabilize copper in a higher oxidation state. This allows copper ions to efficiently transfer electrons, which are crucial for various biological functions. Such stabilization often depends on how these ions interact with surrounding atoms and molecules within the complex biological environment.

Square Planar Geometry

Square planar geometry is a common structure for many metal complexes, including some involving Cu(III) ions. In this type of configuration, the central metal ion, like copper, is situated at the center of a square formed by four ligands. The geometry is more common in d extsuperscript{8} metal ions, such as those with partially filled d orbitals, like copper. The distinctive square planar structure results from the orbital splitting that occurs, where the central metal's d orbitals are split into different energy levels. This configuration often leads to a low-spin state, where electrons are paired with minimal unpaired electrons. It also provides efficient orbital overlap which contributes to the stability of this geometric arrangement. Understanding why certain metal ions adopt this configuration helps in predicting their reactivity and magnetic properties.

Diamagnetic vs Paramagnetic

When assessing whether a compound is diamagnetic or paramagnetic, it boils down to the electron configuration and d orbital occupancy of the central metal ion. In a compound, diamagnetism is characterized by the absence of unpaired electrons, which means all the electrons are paired. As a result, these substances are not attracted to magnetic fields and can even be slightly repelled. Many Cu(III) complexes with a square planar geometry are typically diamagnetic because the splitting of their d orbitals results in all paired electrons. Conversely, paramagnetism occurs when there are unpaired electrons, making the substance attracted to magnetic fields. For instance, copper in its +3 oxidation state, especially in a square planar arrangement, often results in a low-spin, diamagnetic compound due to electron pairing in the lower energy d orbitals. Such knowledge is crucial for predicting how these substances will behave in the presence of a magnetic field.

Complex Ion Naming

The naming of complex ions is systematic and follows specific conventions to clarify the composition and structure of the compound. For a compound such as \( \mathrm{K}_{3} \mathrm{CuF}_{6} \), the name provided reflects its components and their stoichiometry. This compound is named Potassium hexafluorocuprate(III), which indicates several key things:

• "Potassium" refers to the three potassium ions that balance the charge of the complex ion.
• "Hexafluoro" signifies that there are six fluoride ligands attached to the central metal ion.
• "Cuprate(III)" specifies copper as the central metal ion in a +3 oxidation state.

Such naming conventions help chemists and students easily understand the composition of the compound and its structure, aiding in further study or applications. Mastery of these conventions is essential for clarity and precision in scientific communication.