Q.Which of the following complexes are homoleptic?

Concept: Homoleptic complexes contain only one type of ligand bound to the metal centre.

Step 1: Check each complex for the number of distinct ligand types.

• (i) $[Co(NH_3)_6]^{3+}$ — only ammonia ligands → homoleptic.
• (ii) $[Co(NH_3)_4Cl_2]^{+}$ — two different ligands (NH$_3$ and Cl$^-$) → heteroleptic.
• (iii) $[Ni(CN)_4]^{2-}$ — only cyanide ligands → homoleptic. …

The term homoleptic comes from Greek roots: homo (same) and leptos (taken/held). In coordination chemistry, a homoleptic complex is one where the metal ion is bound to only one kind of ligand. If even two different types of ligands are present, the complex is heteroleptic.

This is a classification based purely on ligand identity — not on charge, geometry, or oxidation state. So the task is simply to check each complex: does it contain only one type of ligand, or more than one?

Let’s examine each option.

1. Option (i): $[Co(NH_3)_6]^{3+}$

   The only ligand here is ammonia ($NH_3$). All six coordination sites are occupied by the same ligand.

   → Homoleptic.

2. Option (ii): $[Co(NH_3)_4Cl_2]^{+}$

   Two different ligands are present: ammonia ($NH_3$) and chloride ($Cl^-$). Four sites have $NH_3$, two have $Cl^-$.

   → Heteroleptic.

3. Option (iii): $[Ni(CN)_4]^{2-}$

   The only ligand is cyanide ($CN^-$). All four coordination sites are identical in ligand type.

   → Homoleptic.

4. Option (iv): $[Ni(NH_3)_4Cl_2]$

   Again, two different ligands: ammonia and chloride. Even though the complex is neutral, the ligand set is mixed. …

Concept: Homoleptic vs Heteroleptic Complexes

A homoleptic complex contains only one type of ligand bonded to the central metal atom/ion.

A heteroleptic complex contains two or more different types of ligands.

Method: Ligand-Type Inspection

Steps:

1. List all ligands attached to the central metal in the given complex.
2. Count the distinct types of ligands (ignore the number of each — only variety matters).
3. If exactly one type → homoleptic. If more than one type → heteroleptic.

Applying to each option:

| Complex | Ligands present | Number of ligand types | Result |

|---|---|---|---| …

Common Mistakes on Homoleptic vs. Heteroleptic Complexes

The Concept in One Line

A homoleptic complex has only one type of ligand attached to the central metal atom/ion. A heteroleptic complex has two or more different types of ligands.

Mistake #1: Confusing "homoleptic" with "only one ligand molecule"

The error:

Students think a complex is homoleptic if it contains only one molecule of a ligand (e.g., $[Co(NH_3)_6]^{3+}$ has 6 NH₃ molecules, but some think "one type" means "one molecule").

Why it's wrong:

"One type" refers to the chemical identity of the ligand, not the number of ligand molecules. $[Co(NH_3)_6]^{3+}$ has six identical NH₃ ligands — it is homoleptic.

How to avoid:

• Ask: Are all ligands chemically the same?
• Count the kinds of ligands, not the total number.

Mistake #2: Thinking charge or coordination number determines homoleptic nature

The error:

Students assume that if a complex has a charge (like $[Ni(CN)_4]^{2-}$) or a specific coordination number, it must be homoleptic.

Why it's wrong:

Charge and coordination number are unrelated to ligand diversity. $[Ni(CN)_4]^{2-}$ is homoleptic because all four ligands are CN⁻, not because it's charged.

How to avoid:

• Ignore charge, geometry, and coordination number.
• Focus only on whether the ligands are all the same.

Mistake #3: Misidentifying neutral complexes as heteroleptic

The error:

A neutral complex like $[Ni(NH_3)_4Cl_2]$ is often mistakenly called homoleptic because it is neutral.

Why it's wrong:

Neutrality does not imply ligand uniformity. Here, NH₃ and Cl⁻ are two different ligands — so it is heteroleptic.

How to avoid:

• List the ligands explicitly: NH₃ and Cl⁻ are different.
• If the list has more than one entry → heteroleptic.

Mistake #4: Overlooking the ligand identity in coordination compounds

The error: …