Problem 20 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Which of the following is an example of homoleptic complex? (a) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3}\) (b) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]\) (c) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right]\) (d) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right] \mathrm{Cl}_{2}\)

Step-by-Step Solution

Answer

Option (a) is an example of a homoleptic complex.

Step 1: Understand the Definition

A homoleptic complex is a coordination compound where a metal atom is complexed with only one type of ligand. In simpler terms, all the ligands in the coordination sphere of the metal are identical.

Step 2: Analyze Option (a)

Consider the complex \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3} \). Here, the cobalt metal is surrounded by six ammonia \( \left( \mathrm{NH}_{3} \right) \) molecules, all identical ligands. Therefore, this is a homoleptic complex.

Step 3: Analyze Option (b)

In the complex \( \left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right] \), the platinum metal is coordinated with both ammonia \( \left( \mathrm{NH}_{3} \right) \) and chloride \( \mathrm{Cl} \) ligands. Since there are two different types of ligands, it is not homoleptic.

Step 4: Analyze Option (c)

The complex \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \) has cobalt surrounded by ammonia and chloride ligands, which makes it a heteroleptic complex (different types of ligands), not homoleptic.

Step 5: Analyze Option (d)

For \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right] \mathrm{Cl}_{2} \), the cobalt is coordinated with both ammonia and chloride ligands, indicating that it is also not homoleptic.

Step 6: Identify the Homoleptic Complex

Based on the analysis, option (a) \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right] \mathrm{Cl}_{3} \) is the only complex where the central metal is surrounded by identical ligands. Thus, it is the example of a homoleptic complex.

Key Concepts

Coordination Compounds

Coordination compounds are fascinating entities in chemistry. They consist of a central metal atom or ion, surrounded by non-metal atoms or molecules known as ligands. These ligands are bonded to the metal through coordinate covalent bonds, which involve both electrons for bonding coming from the ligand. Coordination compounds are crucial in various chemical processes and applications, such as in catalysis, biological systems, and material sciences.

The structure of coordination compounds is often represented by square brackets, with the inner sphere consisting of the metal and its directly attached ligands. For example, in the homoleptic complex \([\mathrm{Co}(\mathrm{NH}_{3})_{6}] \mathrm{Cl}_{3}\), cobalt is surrounded by six identical ammonia molecules, forming the coordination sphere.

• The coordination number refers to the number of ligand donor atoms attached to the metal center.
• Homoleptic complexes have only one type of ligand, while heteroleptic complexes feature different kinds of ligands.

Understanding the variety of structures and reactivities of coordination compounds helps unravel complex chemical behaviors and helps design new materials for specific functions.

Metal-Ligand Bonding

Metal-ligand bonding is a cornerstone of the study and understanding of coordination compounds. The bond between the metal and ligand is known as a coordinate or dative bond. In these bonds, the ligand donates a pair of electrons to the vacant orbitals of the metal. This process is similar to a covalent bond, but with the origin of the electron pair clearly from the ligand.

The nature of metal-ligand bonding can;

• Influence the physical and chemical properties of the compound.
• Affect color, magnetism, and reactivity.
• Guide the geometry and orientation of molecules within the compound

Depending on the types of ligands and metals involved, different coordination geometries like octahedral, square planar, or tetrahedral can form. In our example, the cobalt in \([\mathrm{Co}(\mathrm{NH}_{3})_{6}] \mathrm{Cl}_{3}\) forms an octahedral geometry, achieving stability and balance by surrounding itself with six ammonia molecules.

Chemical Ligands

Chemical ligands are critical players in forming coordination compounds. They can be atoms, ions, or molecules that donate an electron pair to the metal center, stabilizing the overall complex. Ligands play a key role in determining the characteristics and functions of the coordination compound.

There are various types of ligands based on their size, charge, and the number of donor atoms. For example:

• Monodentate ligands, like ammonia (\(\mathrm{NH}_{3}\)), which donate one electron pair from a single atom.
• Bidentate ligands, which can donate electron pairs from two atoms within the same molecule.
• Polydentate ligands, which donate multiple pairs, forming chelates that create highly stable structures.

When analyzing a homoleptic complex like \([\mathrm{Co}(\mathrm{NH}_{3})_{6}] \mathrm{Cl}_{3}\), the entire complex is stabilized by the six identical ligands, showing how ligands influence the properties and stability of coordination compounds.