Problem 98 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following will exhibit geometrical isomerism? (M stands for a metal, and a and \(\mathrm{b}\) are achiral ligands, (1) \(\mathrm{Ma}_{2} \mathrm{~b}_{2}\) (2) \(\mathrm{Ma}_{4} \mathrm{~b}_{2}\) (3) \(\mathrm{Ma}_{5} \mathrm{~b}\) (4) \(\mathrm{Ma}_{6}\) (a) 1 and 2 (b) 2 and 3 (c) \(\mathrm{l}\) and 3 (d) 2 and 4

Step-by-Step Solution

Answer

Option (a) 1 and 2 will exhibit geometric isomerism.

Step 1: Understanding Geometric Isomerism

Geometric isomerism occurs in coordination compounds where ligands are arranged differently around a central metal atom, leading to different spatial arrangements while maintaining the same connectivity. This type of isomerism is common in square planar and octahedral complexes but not seen in tetrahedral or linear complexes.

Step 2: Analysis of Each Composition

Let's analyze each complex: 1. \(\text{Ma}_{2}\text{b}_{2}\): This has an octahedral geometry possibility with ligands positioned as cis or trans.2. \(\text{Ma}_{4}\text{b}_{2}\): This can also form geometric isomers with ligands as cis or trans in an octahedral setting.3. \(\text{Ma}_{5}\text{b}\): This configuration does not allow for geometric isomerism, as only one type of arrangement is possible around the central metal.4. \(\text{Ma}_{6}\): In this configuration, no geometric isomerism is possible as all ligands are the same.

Step 3: Identifying Geometrical Isomers

Based on the analysis, complexes \(\text{Ma}_{2}\text{b}_{2}\) and \(\text{Ma}_{4}\text{b}_{2}\) exhibit geometric isomerism due to their potential to have cis and trans configurations. \(\text{Ma}_{5}\text{b}\) and \(\text{Ma}_{6}\) cannot exhibit geometric isomerism.

Step 4: Selecting the Correct Options

The options (a) 1 and 2 match our findings, where both can exhibit geometric isomerism. None of the other provided pairs match the possibility of geometric isomerism.

Key Concepts

Octahedral Complexes

Octahedral complexes are an intriguing class of coordination compounds where six ligands bond to a central metal atom. The spatial arrangement of these ligands resembles the shape of two pyramids base-to-base, creating eight equilateral triangle faces. This geometric configuration is incredibly important in the study and understanding of coordination chemistry.
A common occurrence with these complexes is the formation of geometric isomers. This occurs because the ligands can be arranged in different ways, resulting in various possible geometrical shapes.
For example:

• Cis isomer, where similar ligands are adjacent to each other.
• Trans isomer, where similar ligands are opposite each other.

Such variability in arrangements can lead to differences in chemical and physical properties, even if the chemical formula remains unchanged. These features make octahedral complexes a fascinating subject of study in inorganic chemistry.

Coordination Compounds

Coordination compounds are formed when a central atom, usually a metal, is surrounded by a number of molecules or ions. These surrounding entities, known as ligands, have lone pairs of electrons that they donate to the central metal atom, forming coordinate covalent bonds. This unique bonding formation creates a distinct special property, often leading to the stunning colors and structures seen in these compounds.
The central metal and its ligands together form what is known as the coordination sphere, a key part of these compounds. The coordination number is the count of ligand attachments to the central metal atom. In octahedral complexes, this number is typically six.
Understanding how these compounds work requires recognizing different types of ligands and how they interact. Ligands can be monodentate, bidentate, or polydentate, depending on how many binding sites they have."Coordination compounds" have myriad applications, ranging from catalysts in chemical reactions to components in medicinal chemistry.

Isomerism in Chemistry

Isomerism is a fascinating concept that illustrates how compounds with the same chemical formula can have different structures or arrangements. When it comes to coordination compounds, isomerism plays a crucial role in creating diverse substance properties and reactions.
Geometric isomerism, specifically, involves differences in spatial arrangements of the ligands within the complex. Although the connectivity remains the same, the different orientations can lead to markedly different chemical properties.
In the context of octahedral complexes, geometric isomerism often manifests as cis-trans isomerism. In a cis configuration, similar ligands are adjacent to each other, while in a trans configuration, they are positioned directly opposite. These seemingly simple differences result in distinct behaviors in chemical reactions, boiling points, solubility, and more.
Understanding isomerism is vital for chemists, particularly in areas related to pharmaceuticals, materials science, and catalysis. It aids in predicting and explaining the behavior of various compounds under different conditions.