Strong Field vs Weak Field Ligands Explained

 

❓ Concept Question

How do ligand strength and $d$-electron configuration decide hybridization and magnetic nature in coordination compounds?

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🖼 Concept Image

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✍️ Short Concept

This concept is based on:

👉 Oxidation state of central metal
👉 $d^n$ configuration
👉 Strong field vs weak field ligands
👉 Hybridization in octahedral complexes.

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🔷 Step 1 — Oxidation State of Metal 💯

First step in coordination compounds:

👉 Calculate oxidation state of central metal.

Formula logic:

$$\text{Metal charge + ligand charges = overall charge}$$

This helps determine:

$$d^n \text{ configuration}$$

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🔷 Step 2 — d-Electron Configuration

After oxidation state:

👉 Write $d^n$ configuration.

Examples:

$$Fe^{3+} \rightarrow d^5$$
$$Co^{3+} \rightarrow d^6$$
$$Mn^{3+} \rightarrow d^4$$

This decides number of possible unpaired electrons.

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🔷 Step 3 — Ligand Strength

Ligands decide electron pairing.

Strong Field Ligands

$$CN^- ,\ CO,\ NO_2^-$$

👉 Cause pairing of electrons

Weak Field Ligands

$$F^- ,\ Cl^- ,\ H_2O$$

👉 Do not cause pairing

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🔷 Step 4 — Hybridization in Octahedral Complex

For strong field ligands:

$$d^2sp^3$$

👉 Inner orbital complex

For weak field ligands:

$$sp^3d^2$$

👉 Outer orbital complex

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🔷 Step 5 — Magnetic Nature

If unpaired electrons present:

👉 Paramagnetic

If all electrons paired:

👉 Diamagnetic

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🔷 Step 6 — JEE Trap Alert 🚨

❌ Strong ligand dekh ke direct diamagnetic assume kar lena

❌ $d^n$ configuration galat nikal dena

❌ $F^-$ ko strong field ligand maan lena

❌ Hybridization aur magnetic nature confuse kar dena

Remember:

$$\text{Ligand strength decides pairing}$$

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✅ Final Takeaway

For coordination compound problems:

$$\boxed{\text{O.S.} \rightarrow d^n \rightarrow \text{Ligand strength} \rightarrow \text{Hybridization}}$$

Always:

$$\text{Check unpaired electrons at the end}$$

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⭐ Golden JEE Insight

If ligand is strong:

$$d^2sp^3$$

If ligand is weak:

$$sp^3d^2$$

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🔗 Related Topics

• Crystal Field Theory 
• Strong vs Weak Ligands 
• Hybridization in Coordination Compounds