Class 12 Chemistry Coordination Compounds Notes

Class 12 Chemistry Coordination Compounds Notes

5.1 Werner’s Theory of Coordination Compounds

  • Developed by Alfred Werner (1893)
  • Explained structure and bonding of coordination compounds
  • Key Points:
    1. Metal ions exhibit primary and secondary valencies
      • Primary valency = oxidation state (ionic bonds)
      • Secondary valency = coordination number (coordinate bonds)
    2. Ligands are atoms, ions, or molecules bonded to metal ions

5.2 Definitions of Important Terms

  • Ligand: Molecule or ion that donates electrons to metal (e.g., NH₃, H₂O, CN⁻)
  • Coordination Number: Number of ligand donor atoms attached to central metal
  • Complex Ion: Charged species formed by central metal and ligands
  • Chelate: Complex with a ligand forming more than one bond to metal
  • Coordination Sphere: Central metal + attached ligands

5.3 Nomenclature of Coordination Compounds

Rules:

  1. Name ligands first, then metal
  2. Neutral ligands: Use full name (e.g., aqua for H₂O, ammine for NH₃)
  3. Anionic ligands: End with -o (e.g., chloro, cyano)
  4. Metal name: Use oxidation state in Roman numerals
  5. Use prefixes (di-, tri-, tetra-) for multiple ligands

Example:[Fe(CN)6]3−⇒Hexacyanoferrate(III)[Fe(CN)_6]^{3-} \Rightarrow Hexacyanoferrate(III)[Fe(CN)6​]3−⇒Hexacyanoferrate(III)

5.4 Isomerism in Coordination Compounds

Types of Isomerism

  1. Structural Isomerism
    • Ionization isomerism: Different ions outside the coordination sphere
    • Linkage isomerism: Ligand binds through different donor atoms (e.g., NO₂⁻ binds via N or O)
    • Coordination isomerism: Exchange of ligands between cation and anion
    • Hydrate isomerism: Water inside or outside coordination sphere
  2. Stereoisomerism
    • Geometrical isomerism: cis/trans or fac/mer
    • Optical isomerism: Non-superimposable mirror images

5.5 Bonding in Coordination Compounds

  • Coordinate (dative covalent) bond: Ligand donates lone pair to metal
  • Crystal Field Theory (CFT)
    • Explains color, magnetism, and geometry
    • Octahedral, tetrahedral, square planar geometries
    • Splitting of d-orbitals under ligand field leads to absorption of light → color

5.6 Bonding in Metal Carbonyls

  • Metal carbonyls: Metal + CO ligands
  • Bonding:
    1. σ-donation: CO donates electron pair to metal
    2. π-back bonding: Metal donates electron density back to CO antibonding orbital
  • Example: Ni(CO)₄, Fe(CO)₅

5.7 Importance and Applications of Coordination Compounds

  1. Industrial catalysts: [Co(NH₃)₆]³⁺, [Ni(CO)₄]
  2. Analytical chemistry: Detection of ions (e.g., [Fe(CN)₆]³⁻)
  3. Biological role: Hemoglobin (Fe), Chlorophyll (Mg)
  4. Medicinal use: Cisplatin (anticancer drug)