Problem 82 - A Complete Resource Book in Chemistry for JEE Main

Question

The formula of tetrachlorodiammineplatinum(IV), is (a) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2}\right] \mathrm{Cl}_{4}\) (b) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{4}\right]\) (c) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right] \mathrm{Cl}_{2}\) (d) \(\mathrm{K}_{4}\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{4}\right]\)

Step-by-Step Solution

Answer

The correct formula is (b) \([\text{Pt}(\text{NH}_3)_2\text{Cl}_4]\).

Step 1: Identify the Coordination Number

The compound name is tetrachlorodiammineplatinum(IV). 'Diammine' implies the presence of 2 ammonia (\(\text{NH}_3\)) ligands. 'Tetrachloro' indicates 4 chlorine (\(\text{Cl}\)) ligands are coordinated with platinum. 'Platinum(IV)' suggests platinum is in a +4 oxidation state.

Step 2: Analyze the Coordination Sphere

The coordination number for platinum here is 6 because there are 4 chloride and 2 ammonia groups surrounding it. This means the complex has the form \([\text{Pt}(\text{NH}_3)_2\text{Cl}_4]\).

Step 3: Check for Additional Counter Ions

Since platinum is in a +4 oxidation state, the complex itself does not need any external chloride ions as counter ions to balance the charge within the bracket, indicating the presence of just one coordination sphere.

Step 4: Eliminate Incorrect Options

Based on the understanding that the correct complex formula with a coordination number of 6 is \([\text{Pt}(\text{NH}_3)_2\text{Cl}_4]\), we look at the options: (a) \([\text{Pt}(\text{NH}_3)_2]\text{Cl}_4\) has external chloride ions which doesn't fit; (b) \([\text{Pt}(\text{NH}_3)_2\text{Cl}_4]\) fits the coordination sphere with no counter ions. (c) and (d) have external chloride or complex ions which do not fit our deduction.

Key Concepts

Coordination Number

In coordination chemistry, the coordination number is the total number of ligand atoms that are directly bonded to the central metal atom in a coordination complex. It is an essential concept to understand because it gives us insight into the geometry and stability of the complex.
In the compound tetrachlorodiammineplatinum(IV), the term 'diammine' indicates the presence of two ammonia (\(\text{NH}_3\)) ligands. 'Tetrachloro' shows four chlorine (\(\text{Cl}\)) ligands are attached to the platinum atom. Together, these ligands result in a coordination number of 6, suggesting that 6 atoms or groups are coordinated to platinum. Understanding the coordination number is crucial for predicting physical and chemical properties of the complex.

Oxidation State

The oxidation state refers to the charge of the central atom in a coordination complex when all its ligands are removed along with the electrons they shared with the central atom. It's a vital factor that influences the chemical behavior of the metal center.
The name tetrachlorodiammineplatinum(IV) tells us that platinum has an oxidation state of +4. This is derived because 'Platinum(IV)' directly indicates the oxidation state as part of the complex's formal naming. Knowing the oxidation state helps in understanding not only the charge balance in the compound but also its reactivity with other substances.

Coordination Sphere

The coordination sphere of a complex refers to the central metal atom and its coordinated ligands, as designated by brackets, enclosing these components in the complex's formula. This crucial zone determines much of the chemical identity and functionality of the coordination complex.
In the compound \([\text{Pt}(\text{NH}_3)_2\text{Cl}_4]\), the coordination sphere consists of two ammonia molecules and four chloride ions directly bonded to the platinum. The importance lies in identifying this sphere because it helps in predicting the chemical reactions involving the complex and the stability of the coordination bonds. Furthermore, understanding the configuration within the coordination sphere allows chemists to infer the complex's geometric structure, contributing to its unique properties.