Question

In your own words explain why (a) \(\mathrm{H}_{2} \mathrm{~N}-\left(\mathrm{CH}_{2}\right)_{3}-\mathrm{NH}_{2}\) is a bidentate ligand. (b) \(\mathrm{AgCl}\) dissolves in \(\mathrm{NH}_{3-}\) (c) there are no geometric isomers of tetrahedral complexes.

Short answer

(a) The ligand is bidentate because it can form two bonds with a metal through two nitrogen atoms. (b) AgCl dissolves in NH3 due to the formation of a soluble complex ion. (c) Tetrahedral complexes do not have geometric isomers because all positions are equivalent.

Step-by-step solution

Understanding Bidentate Ligands

A bidentate ligand is a molecule that can form two bonds with a central metal atom. The given compound, \(\mathrm{H}_{2}\mathrm{N}-\left(\mathrm{CH}_{2}\right)_{3}-\mathrm{NH}_{2}\), contains two nitrogen atoms, each with a lone pair of electrons. These two nitrogen atoms can simultaneously coordinate with the central metal, forming two bonds, thus acting as a bidentate ligand.

Dissolution of AgCl in NH3

Silver chloride (\(\mathrm{AgCl}\)) dissolves in ammonia (\(\mathrm{NH}_{3}\)) due to the formation of a complex ion. Ammonia acts as a ligand that coordinates with silver ions (\(\mathrm{Ag}^{+}\)) to form the complex ion \(\mathrm{[Ag(NH}_3)_2]^+\). This complex ion formation is more soluble than \(\mathrm{AgCl}\), causing \(\mathrm{AgCl}\) to dissolve.

Lack of Geometric Isomers in Tetrahedral Complexes

Geometric isomerism arises when a molecule can have different spatial arrangements due to the orientation of its ligands. In tetrahedral complexes, all four positions are equivalent, meaning there are no different spatial arrangements possible. As a result, tetrahedral complexes cannot exhibit geometric isomerism.

Key concepts

Bidentate Ligand

Imagine a molecule that acts like a pair of tongs, gripping a metal tightly at two spots. A bidentate ligand, like \( \mathrm{H}_{2}\mathrm{N}-(\mathrm{CH}_{2})_{3}-\mathrm{NH}_{2} \), works just like that. It has two nitrogen atoms, and each carries a lone pair of electrons. These electrons are free to interact, or "coordinate," with a central metal atom. This ability to form two separate bonds with a single metal makes this molecule a bidentate ligand.
Without needing extra parts, it can effectively grip the metal at two points.

• **Bidentate**: 'bi' meaning two, 'dentate' meaning teeth or points.
• **Ligand**: A molecule that donates electrons to a metal atom.

Think of it like two hands holding onto a pole, providing a tighter, more secure hold.

Complex Ion Formation

Silver chloride (\( \mathrm{AgCl} \) ) is typically not very soluble in water. However, when placed in ammonia (\( \mathrm{NH}_3 \) ), it dissolves! This is due to complex ion formation. Ammonia molecules provide lone pairs of electrons to the metal ion, forming a complex ion called \( \mathrm{[Ag(NH}_3)_2]^+ \). In this configuration, the silver ion (\( \mathrm{Ag}^+ \) ) is more stable and soluble.
This process demonstrates the power of ligands like ammonia, changing the metal's properties by forming a more soluble compound.

Geometric Isomerism

Geometric isomerism involves different spatial arrangements of atoms within a molecule. However, not all compounds can display this form of isomerism. Tetrahedral complexes are one such example, as they have all four ligand positions equivalent. No matter how one tries to rearrange the ligands in a tetrahedral structure, there can be no different spatial orderings because all four positions are symmetric.
As such, tetrahedral complexes simply cannot have geometric isomers, making them quite straightforward compared to other structures where branching arrangements are possible.

Tetrahedral Complexes

When we talk about tetrahedral complexes, picture a pyramid with a triangular base. At its center sits the metal atom, surrounded by four ligands perched at the vertices. But why "tetrahedral"? The geometry comes from the angles between ligands, distributed evenly in three-dimensional space.
This geometry brings about distinct characteristics:

• All positions are symmetrical.
• No possible geometric isomers (unlike square-planar or octahedral complexes).

These features lend simplicity to tetrahedral complexes, contrasting the myriad possibilities found in more complex geometries.

Ligand Coordination

At the heart of coordination chemistry lies the concept of ligand coordination. This process involves ligands donating electron pairs to a metal ion. The bond that forms is called a coordinate bond, characterized by its strength and stability.
Each ligand can create a number of coordinate bonds with the central atom depending on its structure:

• **Donation of electrons** explains how stable complexes form.
• **Interaction strength** defines the complex's solubility and reactivity.

By exploring different ligand-metal combinations, chemists can synthesize compounds with specific properties, harnessing a remarkable control over chemical reactivity and stability.