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Coordination Compounds – High Return Revision Notes

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Coordination Compounds – High Return Revision Notes

Coordination chemistry is a scoring chapter if patterns are recognized instead of memorized. This revision focuses on structure–property logic, standard formulas, and repeated JEE & Board traps.

1. Basic Terminology (Must-Know)

  • Coordination entity: Central metal atom/ion + surrounding ligands
  • Ligand: Electron pair donor (Lewis base)
  • Coordination number (CN): Number of donor atoms bonded to metal
  • Oxidation state: Charge on metal assuming ligands are neutral/ionic
  • Complex ion vs neutral complex: Based on overall charge

2. Ligands – Classification & Key Exceptions

Type Examples Exam Notes
Monodentate NH₃, Cl⁻, CN⁻ CN⁻ is strong field ligand
Bidentate en, ox²⁻ Chelation ↑ stability
Ambidentate NO₂⁻, SCN⁻ Causes linkage isomerism

3. Isomerism in Coordination Compounds (High Yield)

A. Structural Isomerism

  • Ionization: Exchange between inner & outer sphere ions
  • Linkage: Ambidentate ligand coordination site change
  • Coordination: Exchange between complex cation & anion

B. Stereoisomerism (Most Asked)

General Formula Geometry Geometrical Isomerism Optical Isomerism
Ma₆ Octahedral ❌ No ❌ No
Ma₅b Octahedral ❌ No ❌ No
Ma₄b₂ Octahedral ✅ cis / trans ❌ No
Ma₃b₃ Octahedral ✅ fac / mer ❌ No
Ma₂b₂c₂ Octahedral ✅ Yes ✅ Possible
[M(en)₃] Octahedral ❌ No ✅ Yes (Δ, Λ)

4. Bonding Theories (Exam Angle)

  • VBT: Inner orbital = strong ligand, pairing occurs
  • CFT: Explains color, magnetism via Δ₀ and Δₜ
  • CFSE (Octahedral):
    CFSE = (−0.4 × nt₂g + 0.6 × neg)Δ₀

5. Magnetic Moment

Spin-only formula:
μ = √[n(n + 2)] BM
where n = number of unpaired electrons

6. Colour of Complexes (Very Repeated)

  • Due to d–d transitions
  • Higher Δ → absorption of higher energy → complementary color seen
  • d⁰ and d¹⁰ → colorless

7. Common Student Pain Points (Fix These)

  • Do NOT confuse oxidation state with coordination number
  • Square planar complexes → mostly d⁸ (Ni²⁺, Pd²⁺, Pt²⁺)
  • Optical isomerism requires absence of plane of symmetry
  • Strong field ligands increase Δ → pairing increases

✔ Designed for last-week revision
✔ Covers >90% asked patterns
✔ Concept compression without loss of clarity

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