Coordination Chemistry – Class 12 Comprehensive Study Guide

1. Introduction to Coordination Chemistry

Coordination chemistry deals with complex compounds formed when a central metal ion binds to surrounding molecules or ions (ligands) via coordinate covalent bonds.

Key Features of Coordination Compounds:
– Metal ions surrounded by ligands.
– Coordination bonds formed by ligand electron donation.
– Exhibit isomerism, color, magnetism, and reactivity variations.

2. Important Terminology

(a) Coordination Entity: A species consisting of a central metal ion bonded to ligands within square brackets.
Example: [Fe(CN)₆]³⁻

(b) Central Metal Ion: A metal atom/ion capable of binding ligands.
Example: Fe in [Fe(CN)₆]³⁻.

(c) Ligands: Molecules or ions donating electron pairs to the central metal ion.

Types of Ligands:
– Monodentate: NH₃, Cl⁻, CN⁻ (bind through one atom).
– Bidentate: Ethylenediamine (en) (bind through two atoms).
– Polydentate: EDTA (bind through multiple donor atoms).
– Ambidentate: SCN⁻ (binds through S or N), NO₂⁻ (binds through N or O).

3. Nomenclature of Coordination Compounds

Rules for Naming:
1. Cation is named first, then anion.
2. Ligands are named alphabetically.
3. Anionic ligands end in ‘-o’ (Chloride → Chloro, Hydroxide → Hydroxo).
4. Neutral ligands retain common names (NH₃ → Ammine, H₂O → Aqua).
5. The oxidation state of metal is in Roman numerals.
6. If the complex is anionic, the metal name ends in ‘-ate’ (Ferrate for Fe, Cuprate for Cu).

Examples:
– [Co(NH₃)₅Cl]Cl₂ → Pentaamminechloridocobalt(III) chloride
– [Ag(NH₃)₂]Cl → Diamminesilver(I) chloride
– K₄[Fe(CN)₆] → Potassium hexacyanoferrate(II)

4. Isomerism in Coordination Compounds

Structural Isomerism:
– Ionization Isomerism: Different ions outside the coordination sphere.
  Example: [Co(NH₃)₅Br]SO₄ & [Co(NH₃)₅SO₄]Br.
– Hydrate Isomerism: Water inside/outside coordination sphere.
  Example: [Cr(H₂O)₆]Cl₃, [Cr(H₂O)₅Cl]Cl₂·H₂O.
– Linkage Isomerism: Ligand binds differently.
  Example: [Co(NO₂)(NH₃)₅]Cl₂ & [Co(ONO)(NH₃)₅]Cl₂.

Stereoisomerism:
– Geometrical Isomerism: [Pt(NH₃)₂Cl₂] → Cis (adjacent) & Trans (opposite).
– Optical Isomerism: Mirror images, non-superimposable.
  Example: [Co(en)₃]³⁺

5. Bonding in Coordination Compounds

– Valence Bond Theory (VBT): Explains hybridization & magnetism.
  Example: [Co(NH₃)₆]³⁺ → d²sp³ hybridization, diamagnetic.

– Crystal Field Theory (CFT):
  – d-Orbital Splitting explains color & stability.
  – Octahedral: t_₂g (low energy) & e_g (high energy).
  – Tetrahedral: Opposite of octahedral.

6. Applications of Coordination Compounds

– Biological Systems:
  – Hemoglobin (Fe) → Oxygen transport.
  – Chlorophyll (Mg) → Photosynthesis.
– Medicinal Uses:
  – Cisplatin ([PtCl₂(NH₃)₂]) → Cancer treatment.
– Analytical Chemistry:
  – EDTA in complexometric titrations.
– Industrial Uses:
  – Nickel complexes in electroplating.

7. Important Questions & Answers

Short Answer Questions:
1. What is a coordination compound?
   – A compound where a central metal ion is bonded to ligands via coordinate bonds.
2. What is a chelating ligand?
   – A ligand that binds through multiple donor atoms, forming a ring.
3. What is the coordination number of Fe in [Fe(CN)₆]⁴⁻?
   – 6 (six cyanide ligands).
4. What is linkage isomerism?
   – Same ligand, different donor atom (e.g., NO₂⁻ vs. ONO⁻).

Long Answer Questions:
1. Explain geometrical and optical isomerism with examples.
2. Describe the differences between Valence Bond Theory and Crystal Field Theory.
3. What are the applications of coordination compounds in medicine and industry?
4. Explain the hybridization of [CoF₆]³⁻ and its magnetic behavior.