Problem 26 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The geometries of the ammonia complexes of \(\mathrm{Ni}^{2+}, \mathrm{Pt}^{2+}\) and \(\mathrm{Zn}^{2+}\) respectively, are (a) octahedral, square planar and tetrahedral (b) square planar, octahedral and tetrahedral (c) tetrahedral, square planar and octahedral (d) octahedral, tetrahedral and square planar

Step-by-Step Solution

Answer

The answer is (a) octahedral, square planar, tetrahedral.

Step 1: Understand the complex geometries

Begin by understanding the typical geometries for metal complexes. In coordination chemistry, different metal ions tend to form specific geometries based on their electronic configurations and ligand field stabilization energy.

Step 2: Identify the geometry for Ni^{2+} complexes

For \(\mathrm{Ni}^{2+}\), ammonia complexes are often octahedral due to the preference for coordination number 6, resulting in an octahedral geometry with NH3 ligands being attached.

Step 3: Identify the geometry for Pt^{2+} complexes

Platinum complexes, particularly \(\mathrm{Pt}^{2+}\) with ammonia, are frequently square planar. This is due to the dsp\(^{2}\) hybridization which allows \(\mathrm{Pt}^{2+}\) to adopt a stable square planar geometry.

Step 4: Identify the geometry for Zn^{2+} complexes

Zinc complexes such as \(\mathrm{Zn}^{2+}\) with ammonia typically adopt a tetrahedral geometry due to the coordination number of 4 resulting from its filled \(d\) orbitals, leading to a lack of orbital requirement for a square planar shape.

Step 5: Match the geometries to the options

Now, match the observed geometries (octahedral for \(\mathrm{Ni}^{2+}\), square planar for \(\mathrm{Pt}^{2+}\), and tetrahedral for \(\mathrm{Zn}^{2+}\)) to the available options: - (a) Octahedral, square planar, tetrahedral. - (b) Square planar, octahedral, tetrahedral. - (c) Tetrahedral, square planar, octahedral. - (d) Octahedral, tetrahedral, square planar.

Key Concepts

Metal Complex Geometries

Metal complex geometries describe the spatial arrangement of ligands bound to a central metal atom. Understanding these geometries is crucial in coordination chemistry, as they greatly influence the properties and behavior of metal complexes.
For most transition metals, typical geometries include:

• Octahedral: Involving six ligands symmetrically arranged around the metal ion. This is common in transition metals with a coordination number of 6, such as \( \mathrm{Ni}^{2+} \,\) in ammonia complexes.
• Square Planar: Involving four ligands arranged in a square around the metal. The \( \mathrm{Pt}^{2+} \,\) ion, particularly, prefers this geometry due to its \( \text{dsp}^{2} \,\) hybridization, which allows the formation of stable square-planar complexes.
• Tetrahedral: Featuring four ligands symmetrically distributed in three-dimensional space, as is typical for \( \mathrm{Zn}^{2+} \,\) with a coordination number of 4.

Knowing the geometry helps predict reactivity, color, and magnetic properties. Each geometry is influenced by factors such as the size of the ions, electronic configuration, and strength of the ligands.

Transition Metal Complexes

Transition metal complexes are compounds consisting of a central transition metal ion surrounded by molecules or anions, known as ligands. These complexes are fascinating due to their diverse properties and wide range of applications in fields like catalysis, material science, and bioinorganic chemistry.
Transition metal ions, such as \( \mathrm{Ni}^{2+}, \mathrm{Pt}^{2+}, \,\) and \( \mathrm{Zn}^{2+} \,\) exhibit unique abilities to form various geometries as previously discussed:

• \(\text{Ni}^{2+}\) tends to form octahedral complexes.
• \(\text{Pt}^{2+}\) often forms square planar complexes.
• \(\text{Zn}^{2+}\) typically results in a tetrahedral geometry.

These metals possess partially filled \(d\)-orbitals, allowing them to form specific bonds with ligands. The metal ions' ability to bond with multiple ligands leads to various oxidation states and colors due to d-d electronic transitions. Differences in geometry also significantly impact the electronic, magnetic, and optical properties of these complexes.

Ligand Field Theory

Ligand Field Theory (LFT) is essential to understanding how ligand arrangements impact the electronic structure and properties of metal complexes.
LFT extends the crystal field theory, integrating molecular orbital theory principles to help describe complex interactions. Here's a breakdown:

• Splitting of d-Orbitals: LFT describes that in the presence of ligands, the degeneracy of the metal's \(d\)-orbitals is lost, resulting in orbital splitting based on the geometry of the complex. Octahedral fields split the \(d\)-orbitals into a higher energy \(e_{g}\) set and a lower energy \(t_{2g}\) set.
• Stabilization Energy: These energy differences influence the stability and color of the complex, known as ligand field stabilization energy (LFSE).
• Hybridization Influences Geometry: The geometric preference, such as the square-planar geometry of \(\text{Pt}^{2+}\), arises from specific hybridizations (\text{dsp}^{2}) explaining its unique properties compared to tetrahedral or octahedral complexes.

LFT not only predicts the magnetism and stability of transition metal complexes but also provides insights into their reactivity, making it a critical aspect of coordination chemistry.