Question

Among the properties (A) reducing (B) oxidizing (C) complexing, the set of properties shown by \(\mathrm{CN}\) - ion towards metal species is [2004] (a) A, B (b) \(\mathrm{B}, \mathrm{C}\) (c) \(\mathrm{C}, \mathrm{A}\) (d) \(\mathrm{A}, \mathrm{B}, \mathrm{C}\)

Short answer

The correct set of properties for \(\mathrm{CN}^-\) towards metal species is complexing (B, C).

Step-by-step solution

Understand CN- ion

The cyanide ion \((\mathrm{CN}^-)\) is known for its ability to form complexes with metal ions. It has a strong affinity for metals and can act as a ligand, forming strong bonds due to its ability to donate a pair of electrons from the carbon atom.

Evaluate Complexing Property

Since \(\mathrm{CN}^-\) is a well-known ligand, it strongly exhibits the property of complexing with metal ions by donating electron pairs to form stable complexes. This makes it a strong complexing agent.

Assess Oxidizing Property

To determine if \(\mathrm{CN}^-\) is an oxidizing agent, we consider its tendency to accept electrons. However, \(\mathrm{CN}^-\) is already in a reduced state and does not commonly act as an oxidizing agent. Thus, it does not exhibit significant oxidizing properties.

Check Reducing Property

The reducing property involves the ability of a species to donate electrons. While \(\mathrm{CN}^-\) can donate electron pairs in coordination (complexing), it does not usually participate in reactions that involve donating electrons to oxidize another substance. Therefore, it does not demonstrate a significant reducing property.

Conclusion on Properties

Based on the analysis: \(\mathrm{CN}^-\) predominantly shows complexing properties towards metal species and does not significantly exhibit either oxidizing or reducing properties. Thus, option \(\mathrm{B}, \, \mathrm{C}\) is correct.

Key concepts

Understanding Complexation

Complexation is a fundamental concept in coordination chemistry where molecules or ions form a complex by attaching themselves to a central metal ion. This forms a stable structure through coordinate bonds, where the ligands donate electron pairs to the metal ion. The cyanide ion \(\mathrm{CN}^-\) is particularly well-known for its strong complexation ability. It efficiently donates electron pairs from its carbon atom to transition metal ions. This ability to form complexes is used in various industrial processes, such as electroplating, where strong and durable metal coatings are needed. When you think of complexation, envision a spider web where the metal ion is at the center, and the ligands, like \(\mathrm{CN}^-\), are the threads holding everything together.
Complexes formed with cyanide are significant due to their stability. For example, the cyanide ion forms stable complexes with metals such as gold or silver, which is used in gold extraction from ores. This illustrates the power of complexation in chemical applications.

Role of Ligands

Ligands are crucial components in coordination chemistry, acting as the molecules or ions that bind to the central metal ion. They can be as simple as a single atom or as complex as a long-chain molecule.
The cyanide ion, \(\mathrm{CN}^-\), is a classical example of a ligand due to its strong electron pair donating ability. It is categorized as a monodentate ligand, meaning it uses one atom to bind to the metal center, usually through its carbon atom. This donation process creates a coordinate bond with the metal, aiding in the stability of the resulting complex.
Different ligands have varying strengths, known as the "ligand field strength". Cyanide is known for having a high ligand field strength due to its ability to donate electrons effectively, making the complexes it forms very stable. Ligands like \(\mathrm{CN}^-\) play a dual role: they stabilize the metal center and also influence properties such as the color and magnetism of the complex.

Oxidation-Reduction Properties

Oxidation-reduction (redox) reactions are processes where electrons are transferred between species. A reducing agent typically donates electrons, while an oxidizing agent accepts them.
In the context of the cyanide ion \(\mathrm{CN}^-\), it is more known for its complexation rather than its redox behavior. It is not a common oxidizing agent because it does not tend to gain additional electrons. Moreover, as a reducing agent, \(\mathrm{CN}^-\) usually does not participate in reactions that involve donating electrons to oxidize other substances.
In summary, while \(\mathrm{CN}^-\) plays a significant role as a complexing agent, its role in oxidation-reduction reactions is minimal. The focus in educational exercises is often on its ability to form complexes rather than its activity as an oxidizing or reducing agent. This is why, in many of these exercises, only its complexation properties are prominently highlighted.