Problem 47 - A Complete Resource Book in Chemistry for JEE Main

Question

According to IUPAC nomenclature sodium nitroprusside is named as (a) sodium pentacyanonitrosyl ferrate (II) (b) sodium pentacyanonitrosyl ferrate (III) (c) sodium nitroferriccyanide (d) sodium nitroferrocyanide

Step-by-Step Solution

Answer

The correct IUPAC name is (b) sodium pentacyanonitrosyl ferrate (III).

Step 1: Identify the Coordination Complex

Recognize that the compound 'sodium nitroprusside' is a coordination complex containing iron, cyanide, and nitrosyl groups.

Step 2: Determine the Charge on the Metal

In a coordination complex, determine the oxidation state of iron. In sodium nitroprusside, iron is present in a low oxidation state, typically determined by balancing the compound's charge with that of sodium.

Step 3: Analyze the Ligands Present

Identify the ligands attached to the metal center. There are five cyanide ions (CN⁻) and one nitrosyl (NO) ligand coordinating to the iron center.

Step 4: Apply IUPAC Naming Principles

Apply IUPAC nomenclature for coordination compounds, considering the oxidation state of iron and sequence of naming ligands. The name starts with 'sodium,' followed by the ligands and the central atom with its oxidation state.

Step 5: Determine the Correct IUPAC Name

Considering that the complex contains iron in the +3 oxidation state with cyanide and nitrosyl ligands, the correct IUPAC name according to the identified components and rules is 'sodium pentacyanonitrosyl ferrate (III).'

Step 6: Select the Correct Option

Match the IUPAC name derived with the given options: (a), (b), (c), or (d), selecting the one that corresponds to the analyzed nomenclature.

Key Concepts

Coordination Complex

A coordination complex is a fascinating structure in chemistry where a central metal atom or ion successfully bonds to surrounding molecules or ions, termed ligands. In these complexes, the central metal is typically a transition metal. This unique setup is derived from the ability of transition metals to accommodate electrons from multiple surrounding ligands.
Coordination complexes are crucial for understanding various chemical reactions and structures. Metals in these complexes can vary widely but are essential in forming stable compounds with specific properties. Importantly, coordination complexes are pivotal in applications ranging from industrial chemistry to biological systems. In the case of sodium nitroprusside, iron serves as the central metal in the coordination complex, with cyanide and nitrosyl groups as ligands bound to it.

Oxidation State

The oxidation state, or oxidation number, refers to the degree of oxidation of an atom within a compound, signifying the hypothetical charge it would possess if the compound's bonding were completely ionic. This concept is essential for assigning oxidation states accurately in coordination complexes.
To determine the oxidation state of a metal in a coordination complex, it's crucial to balance the charges of the ligands and any counter ions present in the compound. Sodium nitroprusside involves iron in a specific oxidation state wherein it contributes to the stability of the entire compound via its bonds with ligands.
In sodium nitroprusside, the oxidation state of iron is calculated by acknowledging the charges from the ligands and the overall charge balance. This results in iron being in the +3 oxidation state here, as it aids in maintaining the compound's neutrality.

Ligands

Ligands are molecules or ions that attach themselves to a central metal atom in a coordination complex through a process called coordination. These ligands act as electron donors to the metal, creating bonds that are significant for the compound's structure.
There is considerable diversity among ligands:

• Monodentate Ligands: These can attach to the metal at only one bonding site, such as the cyanide ion (CN⁻).
• Multidentate Ligands: Capable of forming multiple bonds with the metal center, like ethylenediamine (en).

For sodium nitroprusside, the ligands in play include five cyanide ions and one nitrosyl group. Each ligand contributes to the overall complex's properties and stabilities by forming robust bonds with the iron atom.

IUPAC Naming Rules

IUPAC (International Union of Pure and Applied Chemistry) naming rules provide a standardized system for naming chemical substances, ensuring coherence and simplicity. These naming conventions are vital for systematic communication within the scientific community.
In coordination chemistry, IUPAC rules help in naming compounds based on various factors including:

• Order of Ligands: Ligands' names are listed alphabetically, preceding the metal's name.
• Metal's Oxidation State: Indicated using Roman numerals in parentheses immediately following the nomenclature of the central metal.

For sodium nitroprusside, naming according to IUPAC involves:

• Starting with the name of the cation 'sodium.'
• Listing ligands alphabetically: 'pentacyano' derived from cyanide ions and 'nitrosyl' from the NO group.
• Finally, stating the metal (iron) as 'ferrate' followed by its oxidation state (III) in parentheses.

Thus, the nomenclature correctly identifies the complex as 'sodium pentacyanonitrosyl ferrate (III).' This precise naming ensures the structure and components are clearly understood.