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

(a) \(\left[\mathrm{Pt}\left(\mathrm{NH}_3\right)_2\right]\mathrm{Cl}_4\) is the correct formula.

Step 1: Understand Coordination Chemistry

In coordination chemistry, a coordination compound consists of a central metal atom or ion surrounded by molecules or anions, known as ligands. For platinum (Pt), it can be coordinated to various ligands such as amines (NH3) and halides (Cl-).

Step 2: Break Down the Complex Name

The complex name 'tetrachlorodiammineplatinum(IV)' can be broken into parts: "tetra" refers to four chloride ligands (Cl) and "diammine" refers to two amine ligands (NH3) coordinated to a central platinum (Pt) ion with an oxidation state of +4.

Step 3: Determine the Coordination Formula

Since 'tetrachloro' indicates four chloride ions, and 'diammine' indicates two ammonia ligands, the complex ion in the question must include both \(\mathrm{NH}_3\) and \(\mathrm{Cl}^-\) ligands coordinated to Pt. Also, Pt(IV) indicates a +4 charge on the platinum.

Step 4: Translate Coordination Name to Formula

The given name translates to the formula where Pt is in the center, surrounded by the specified number of ligands: two NH3 groups and four Cl groups. This matches the complex formula \(\left[\mathrm{Pt}\left(\mathrm{NH}_3\right)_2\right]\mathrm{Cl}_4\).

Step 5: Identify the Correct Option

Among the provided choices, (a) \(\left[\mathrm{Pt}\left(\mathrm{NH}_3\right)_2\right]\mathrm{Cl}_4\) represents the structure with platinum coordinated to two NH3 and four Cl- ions, which satisfies the requirements of the compound name.

Key Concepts

Coordination Compounds

Coordination compounds play a significant role in chemistry, particularly in inorganic chemistry. These compounds arise when a central metal atom or ion is surrounded by molecules or ions, known as ligands. The central metal ion forms coordinate covalent bonds with these ligands through the donation of electron pairs. In coordination chemistry, the metal ion is usually a transition metal, noted for its ability to accommodate a larger number of coordination bonds due to its d orbitals.

These compounds can have diverse structures and properties, influenced by the type of ligands and the coordination number. Coordination number refers to the number of ligand donor atoms attached to the central metal ion. The unique arrangements and interaction of ligands and metal ions contribute to the physical and chemical properties of the coordination compound. Understanding these properties is crucial for fields like materials science, catalysis, and bioinorganic chemistry.

Ligands

Ligands are the molecules or ions that attach to the central metal atom in coordination compounds. They donate electrons to the metal to form coordinate covalent bonds. Ligands are diverse and can vary in charge, size, shape, and the type of donor atoms they possess. Common ligands include simple ions like Cl⁻ and neutral molecules like ammonia (NH₃).

Ligands can be classified based on:

• Charge: Neutral (like NH₃), or charged (like Cl⁻ or CN⁻).
• Number of donor atoms: Monodentate (one donor atom, e.g., NH₃), bidentate (two donor atoms, e.g., en), or polydentate ligands (more than two donor atoms, e.g., EDTA).
• Flexibility: Rigid or flexible, affecting how they bind to the metal.

Ligands influence the stability and reactivity of the coordination compound. They can enhance or modify the metal’s properties, making the study of ligands vital in coordination chemistry.

Oxidation State

The oxidation state in coordination chemistry refers to the charge that the metal atom or ion has within a coordination compound. This is crucial for understanding the compound's chemistry because it affects both the physical properties and reactivity of the compound.

To determine the oxidation state of the metal, consider the charges of the ligands and the overall charge of the complex ion. For example, in the compound tetrachlorodiammineplatinum(IV), platinum has an oxidation state of +4. This means that the platinum ion is formalized as losing four electrons to achieve stability within the compound. Each ligand’s charge contributes to the overall charge:

• The four chloride ions (Cl⁻) each contribute a charge of -1, totaling -4.
• The two ammonia (NH₃) ligands are neutral.

Assessing the oxidation state provides insights into the electron configuration and potential reactions the compound might undergo.

Chemical Formulas

Chemical formulas in coordination chemistry provide a map to understanding the composition and arrangement of atoms in a complex. These formulas denote how ligands and central metal atoms are related within a structure. For coordination compounds, it's crucial to correctly interpret and write their chemical formulas.

Consider the coordination formula for tetrachlorodiammineplatinum(IV),

• The formula starts with the metal ion, in this case, Pt.
• It is followed by the number and type of ligands: two ammonia molecules (NH₃), which are neutral, and directly bond to the central metal, represented as \( ext{(NH}_3\text{)}_2\).
• The four chloride ions (Cl⁻) are coordinated outside the central metal complex, resulting in \( ext{Cl}_4\).

This nomenclature helps correctly identify the chemical identity and allows chemists to predict properties and behavior. Writing and reading chemical formulas accurately in coordination chemistry is key to understanding these intricate structures.