Problem 32 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Consider the coordination compound, \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3} .\) In the formation of this complex, the species which acts as the Lewis acid is: (a) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}\) (b) \(\mathrm{Cl}^{-}\) (c) \(\mathrm{Co}^{3+}\) (d) \(\mathrm{NH}_{3}\)

Step-by-Step Solution

Answer

(c) \(\mathrm{Co}^{3+}\) is the Lewis acid.

Step 1: Understanding Lewis Acids and Bases

A Lewis acid is a chemical species that can accept a pair of electrons, whereas a Lewis base donates a pair of electrons. Coordination compounds often involve metal ions acting as Lewis acids.

Step 2: Identify the Coordination Species

The given compound is \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3}\). This means that \(\mathrm{Co}^{3+}\) interacts with six \(\mathrm{NH}_{3}\) molecules, and \(\mathrm{NH}_{3}\) acts as a Lewis base by donating electron pairs.

Step 3: Determine the Lewis Acid

Since the central metal ion \(\mathrm{Co}^{3+}\) accepts electron pairs from the \(\mathrm{NH}_{3}\) molecules (which act as Lewis bases), \(\mathrm{Co}^{3+}\) is the Lewis acid in this coordination compound.

Key Concepts

Lewis Acid

In coordination chemistry, a Lewis acid is typically a chemical species that is capable of accepting an electron pair. This characteristic makes metals particularly adept as Lewis acids because they have vacant orbitals that can be filled by electrons from other atoms or molecules. In the coordination compound \[\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3},\] the central species \[\mathrm{Co}^{3+}\] acts as a Lewis acid. It accepts electron pairs from surrounding ligands, such as ammonia (\[\mathrm{NH}_{3}\]). These electrons fill the vacant orbitals of the cobalt ion, stabilizing the complex.

• Lewis acids are electron pair acceptors.
• Metal ions often serve as Lewis acids in coordination compounds.
• In this example, \[\mathrm{Co}^{3+}\] is the Lewis acid.

Understanding Lewis acids helps in predicting and explaining the behavior of coordination compounds, as they play a crucial role in their formation and stability.

Lewis Base

A Lewis base is a molecule or ion that donates a pair of electrons to form a chemical bond. In the context of a coordination compound, the electron donation leads to the formation of a coordinate covalent bond, where both electrons in the bond originate from the Lewis base.

• Lewis bases are electron pair donors.
• They are essential in forming coordinate covalent bonds.

In \[\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3},\] ammonia (\[\mathrm{NH}_{3}\]) acts as a Lewis base. It donates its lone pair of electrons to the cobalt ion (\[\mathrm{Co}^{3+}\]), helping to stabilize the compound. Ammonia is a common Lewis base due to its ability to donate electrons readily from its nitrogen atom.Therefore, in any coordination compound, understanding the role of Lewis bases is critical for determining how the compound forms and maintains its structure. They essentially hold the key to the creation of complex molecular geometries by bonding with metal centers.

Coordination Compounds

Coordination compounds consist of a central metal atom or ion, known as the coordination center, surrounded by a set of molecules or ions called ligands. These ligands are bound to the metal atom through coordinate covalent bonds, where the ligand provides both electrons for the bond.

• Central metal ions act as Lewis acids.
• Ligands, acting as Lewis bases, donate electron pairs.
• The combination provides stability to the overall structure.

An example is \[\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3},\] where \[\mathrm{Co}^{3+}\] is at the center, and it's surrounded by six ammonia molecules acting as ligands. Coordination compounds are significant in various chemical and biological processes due to their unique structures and properties.These often form colorful solutions and crystalline solids due to their ability to absorb visible light at specific wavelengths. This property makes them valuable not only in academic study but also in practical applications, such as catalysis, medicine, and material sciences. Understanding coordination compounds helps in developing new chemical substances and applications.