Problem 8 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Among (a) - (d), the complexes that can display geometrical isomerism are: (1) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{3} \mathrm{Cl}\right]^{+}\) (2) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right) \mathrm{Cl}_{5}\right]^{-}\) (3) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}\left(\mathrm{NO}_{2}\right)\right]\) (4) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{ClBr}\right]^{2+}\) (a) (2) and (3) (b) \((4)\) and (l) (c) (3) and (4) (d) (1) and (2)

Step-by-Step Solution

Answer

Option (c): (3) and (4) can show geometrical isomerism.

Step 1: Understanding Geometrical Isomerism

Geometrical isomerism occurs in coordination compounds where the arrangement of ligands can differ around the central atom, resulting in different spatial configurations, such as cis and trans forms.

Step 2: Analyzing Complex 1

The complex \([Pt(NH_3)_3Cl]^+\) involves a coordination number of 4 with square planar geometry. With three identical ligands \((NH_3)\) and one \(Cl^-\), there are no geometrical isomers. Thus, this complex cannot show geometrical isomerism.

Step 3: Analyzing Complex 2

The complex \([Pt(NH_3)Cl_5]^-\) is likely to be octahedral because it is a platinum complex. However, with five identical ligands \((Cl^-)]\), it does not possess any pairs of different ligands necessary for geometrical isomerism. Therefore, this complex also does not show geometrical isomerism.

Step 4: Analyzing Complex 3

The complex \([Pt(NH_3)_2Cl(NO_2)]\) has a coordination number of 4 and can have different spatial arrangements of the \(NH_3\), \(Cl\), and \(NO_2\) ligands, leading to the possibility of cis and trans isomers. Thus, this complex can show geometrical isomerism.

Step 5: Analyzing Complex 4

The complex \([Pt(NH_3)_4ClBr]^{2+}\) typically assumes a coordination number of 6, forming an octahedral geometry. With one \(Cl^-,\) one \(Br^-,\) and four \(NH_3\) ligands, there can be different spatial arrangements of \(Cl^-\) and \(Br^-\) ligands (cis and trans), leading to geometrical isomerism.

Step 6: Selecting the Correct Option

From the above analysis, complexes 3 and 4 can exhibit geometrical isomerism. Thus, the correct answer is option (c): (3) and (4).

Key Concepts

Geometrical Isomerism

Geometrical isomerism is a fascinating aspect of coordination chemistry. It arises when compounds (particularly coordination complexes) display different spatial arrangements of ligands around a central atom. Imagine ligands like tiny magnets that can attach themselves in different patterns around a central metal ion. This can lead to distinct formations, typically referred to as "cis" and "trans" isomers.
For example, in a square planar complex, if two identical ligands are adjacent, they form a cis isomer. Conversely, if they are opposite, they form a trans isomer. Similarly, in octahedral complexes, such spatial arrangements also lead to geometric isomerism.

• Cis isomers have ligands positioned next to each other.
• Trans isomers have ligands located across from each other.

Understanding how these arrangements work is key to recognizing and predicting geometrical isomerism in coordination compounds.

Complex Compounds

Complex compounds play a critical role in coordination chemistry. A complex compound generally consists of a central metal ion bonded to multiple ligands. Ligands, which can be atoms, ions, or molecules, donate electron pairs to the central metal, forming coordination bonds.
These complexes often exhibit different geometries, such as linear, square planar, tetrahedral, or octahedral, depending on the metal ion's coordination number. For example, platinum commonly forms square planar or octahedral complexes, as seen in the original exercise.
Each ligand's identity strongly influences the geometry and properties of the complex.

• Ligands donate electron pairs, stabilizing the complex structure.
• The ligands' arrangement around the metal can impact properties like color, magnetism, and reactivity.

Understanding these geometries and structures helps in predicting the properties and reactivity of complex compounds.

Ligand Arrangement

The arrangement of ligands around a central atom in a coordination complex is crucial in determining its chemical behavior and properties. Ligands can attach themselves in varying sequences, which influences the overall geometry of the complex and whether it can undergo geometrical isomerism.

• In a square planar complex, like some platinum complexes, four coordination sites allow for different arrangements that may lead to geometrical isomerism.
• In an octahedral complex, the six coordination sites provide even more possibilities for arranging ligands.

Different spatial arrangements determine whether the complex can have cis/trans isomers. For instance, the presence of different ligands, such as nitrite \((NO_2)\), amine \((NH_3)\), and halides \((Cl^-, Br^-)\), can create potential isomers in square planar and octahedral settings. Thus, examining ligand types and their positions provides insight into isomerism within complexes.