Problem 93 - A Complete Resource Book in Chemistry for JEE Main

Question

The number of isomers possible for complex \(\mathrm{K}_{2}\) [Pd \(\left.\mathrm{Cl} \mathrm{Br}(\mathrm{SCN})_{2}\right]\) is (a) 1 (b) 2 (c) 3 (d) 4

Step-by-Step Solution

Answer

The number of isomers is 2.

Step 1: Understand the Complex Formula

The given complex is \( \mathrm{K}_{2} [\mathrm{PdClBr(SCN)}_{2}] \). In this complex, Pd is the central metal ion, and it is coordinated with two negatively charged SCN ligands, one chloride ion (Cl\(^{-}\)), and one bromide ion (Br\(^{-}\)). {}In short, you can denote this as \( \left[PdABX_{2}\right] \), where A=Cl, B=Br, and X=(SCN).

Step 2: Identify Types of Isomerism

This complex can exhibit geometric isomerism because the ligands are differently arranged around the central metal ion. In this square-planar configuration, we will explore potential geometric isomers.

Step 3: Determine Geometric Isomers

In a square-planar configuration such as \([PdABX_{2}]\), there are two distinct geometric arrangements possible:1. Cis Arrangement: Both identical ligands (e.g., \(SCN^-\)) located next to each other.2. Trans Arrangement: Both identical ligands are opposite each other.Therefore, the isomers are:- Cis: SCN-SCN adjacent.- Trans: SCN-SCN opposite.

Step 4: Count the Number of Isomers

As identified in Step 3, there are only two possible arrangements (Cis and Trans) for the square-planar complex \([PdClBr(SCN)_{2}]\). Therefore, there are a total of 2 isomers.

Key Concepts

Geometric Isomerism

Geometric isomerism is an important concept in coordination chemistry that arises when ligands are arranged differently around a central metal atom or ion, resulting in different spatial arrangements. This arrangement can massively impact the properties of the compound, such as its color, reactivity, and biological activity. In the case of square-planar complexes, like the one given by \([PdClBr(SCN)_2]\), geometric isomerism is visible as either cis or trans isomers.

• Cis Isomer: In this arrangement, similar ligands are positioned next to each other. This results in a square shape on one side of the central metal ion.
• Trans Isomer: Here, similar ligands are placed opposite each other, creating a linear line through the center of the complex.

Understanding these different types helps in determining the number of geometric isomers possible for a given complex. In our exercise, the number isomers produced are 2 due to the distinct cis and trans arrangements of SCN ligands.

Square-Planar Complexes

Square-planar complexes are a type of coordination compound configuration where four ligands are arranged at the corners of a square around a central metal ion. This geometry is most commonly found with d8 metal ions such as Pt(II), Ni(II), and Pd(II), which is used in the given exercise

The arrangement and geometry of a coordination complex greatly influence its chemical properties. With the metal ion at the center and ligands symmetrically disposed along a plane, these complexes are particularly susceptible to geometric isomerism.

• Provides a rigid structure suitable for displaying cis-trans isomerism.
• Often leads to lower coordination numbers.
• Found frequently in precious metal compounds like those containing platinum and palladium.

Understanding the concept of square-planar structures is essential in assessing the potential isomers a coordination complex can exhibit, as seen in the complex \([PdClBr(SCN)_2]\).

Coordination Chemistry

Coordination chemistry is a fascinating branch of chemistry that deals with the study of complexes formed between metal ions and ligands. These ligands are atoms, ions, or molecules that donate electron pairs to the metal, forming coordinate covalent bonds. The study of these complexes has profound implications on both fundamental chemistry and practical applications.

Legions are crucial in determining the structure and properties of the resulting coordination complex. In coordination chemistry:

• The choice of ligands affects the geometry of the complex, ranging from tetrahedral to octahedral and square-planar forms.
• Determines the types and numbers of possible isomers for a given metal coordination.
• Applications range from catalysis in industrial processes to understanding biological systems.

In the exercise, learning the intricate roles of ligands such as Cl\(^-\), Br\(^-\), and SCN\(^-\) helps in predicting and understanding the isomerism observed in coordination complexes like \([PdClBr(SCN)_2]\). Understanding coordination chemistry is vital for predicting the properties of these complexes and their real-world applications.