Question

Which of the following coordination complex compounds is officially classified as a 'Heteroleptic Complex'?

• A. \( [\text{Fe}(\text{H}_2\text{O})_6]\text{Cl}_3 \)
• B. \( [\text{Co}(\text{NH}_3)_5(\text{Cl})]\text{Cl}_2 \)
• C. \( \text{K}_4[\text{Fe}(\text{CN})_6] \)
• D. \( [\text{Ni}(\text{CO})4] \)

Hint:

To identify homoleptic vs. heteroleptic complexes quickly, look inside the square brackets. If you see two or more distinct chemical formulas listed next to the metal symbol, it is a Heteroleptic Complex. Ignore any counter-ions outside the brackets.

Answer 1

The Correct Option is B

Concept: Coordination complexes are classified into two structural categories based on the variety of ligands bound to the central metal atom:

• Homoleptic Complexes: Complexes in which the central metal atom is bound to only one type of ligand group (e.g., all water molecules or all cyanide ions).
• Heteroleptic Complexes: Complexes in which the central metal atom is bound to more than one type of ligand group simultaneously.

Step 1: Analyze the ligand composition inside the coordination sphere for each option.
Examine the ligands enclosed within the square brackets:

• \( [\text{Fe}(\text{H}_2\text{O})_6]\text{Cl}_3 \): Contains only 6 aqua (\(\text{H}_2\text{O}\)) ligands. [Homoleptic]
• \( \text{K}_4[\text{Fe}(\text{CN})_6] \): Contains only 6 cyanido (\(\text{CN}^-\)) ligands. [Homoleptic]
• \( [\text{Ni}(\text{CO})_4] \): Contains only 4 carbonyl (\(\text{CO}\)) ligands. [Homoleptic]

Step 2: Identify the complex with a mixed ligand environment.
In \( [\text{Co}(\text{NH}_3)_5(\text{Cl})]\text{Cl}_2 \), the coordination sphere contains two completely different types of ligands bound directly to the central Cobalt core: 5 neutral ammine (\(\text{NH}_3\)) molecules and 1 anionic chlorido (\(\text{Cl}^-\)) ion. Because it features a mixed ligand assembly, it is classified as a Heteroleptic Complex.