Introduction to Coordination Chemistry

• Coordination Compounds: Compounds in which a central metal atom/ion is bonded to a set of molecules or ions called ligands.

• Metal can be transition or inner transition element, usually having vacant d-orbitals.

• NEET focuses on types of ligands, coordination numbers, bonding, and applications rather than memorizing all reactions.

Key Concept: The properties of coordination compounds depend on metal, oxidation state, and type of ligands.

Direct Links to Download 2025-26 Chemistry Notes (PDF)

► Click “Download Here” next to your subject to access the free PDF.

Central Metal Atom/Ion

• Usually a transition metal, can have variable oxidation states.

• Must have empty orbitals to accommodate ligands.

• Properties influenced by size, charge, and electronic configuration.

NEET Focus: Conceptual understanding of why transition metals form complex compounds.

Ligands

• Definition: Species (ions or molecules) that donate one or more pairs of electrons to a central metal atom/ion.

• Classification:

  1. Monodentate ligands: donate 1 pair of electrons (e.g., NH₃, Cl⁻)

  2. Bidentate ligands: donate 2 pairs of electrons (e.g., ethylenediamine, oxalate)

  3. Polydentate ligands (Chelates): donate multiple electron pairs (e.g., EDTA⁴⁻)

Conceptual Focus: Understand chelation → enhanced stability of complex.

Coordination Number

• Definition: Number of ligand donor atoms directly bonded to the central metal atom.

• Common numbers: 2, 4, 6

  • 2 → Linear (e.g., [Ag(NH₃)₂]⁺)

  • 4 → Tetrahedral/Square Planar (e.g., [Ni(CO)₄], [Pt(NH₃)₄]²⁺)

  • 6 → Octahedral (e.g., [Fe(CN)₆]³⁻)

NEET Tip: Focus on how ligand size, metal size, and electronic configuration determine geometry.

Nomenclature of Coordination Compounds

• Rules:

  1. Name ligands first (alphabetical order), then metal

  2. Use prefixes to indicate the number of ligands (di-, tri-, tetra-)

  3. Oxidation state of metal in Roman numerals in parentheses

• Examples:

  • [Co(NH₃)₆]Cl₃ → Hexaamminecobalt(III) chloride

  • [Cu(CN)₄]³⁻ → Tetracyanocuprate(I)

NEET Focus: Understanding nomenclature conceptually helps in solving reasoning-based questions.

Bonding in Coordination Compounds

1. Werner’s Theory:

• Metal has primary and secondary valencies (oxidation state and coordination number)

• Explained structural isomerism and bonding in complexes

2. Valence Bond Theory (VBT):

• Ligands donate electron pairs to metal’s hybrid orbitals

• Explains geometry (octahedral, tetrahedral, square planar)

• Conceptual focus: d²sp³, sp³d², dsp² hybridization

3. Crystal Field Theory (CFT):

• Metal-ligand interaction is electrostatic

• d-Orbitals split in energy depending on geometry

• Explains color, magnetic properties, and stability

  • Octahedral → d-orbital split into t₂g & eg

  • Tetrahedral → opposite splitting pattern

NEET Tip: Focus conceptually on why octahedral and tetrahedral complexes are colored (d-d transitions).

Isomerism in Coordination Compounds

1. Structural Isomerism:

   • Ionization Isomerism → Different ions in solution (e.g., [Co(NH₃)₅Br]SO₄ vs [Co(NH₃)₅SO₄]Br)

   • Coordination Isomerism → Ligands exchanged between metal ions

   • Linkage Isomerism → Ligand attached through different atoms (e.g., SCN⁻ through S or N)

   • Hydrate Isomerism → Water molecules inside or outside coordination sphere

2. Stereoisomerism:

   • Geometrical Isomerism: cis/trans arrangement in square planar or octahedral complexes

   • Optical Isomerism: Non-superimposable mirror images

NEET Tip: Conceptually link ligand orientation → type of isomer.

Stability of Coordination Compounds

1. Chelate Effect:

• Polydentate ligands → higher stability due to ring formation

• Example: EDTA forms very stable complexes with Ca²⁺, Fe³⁺

2. Factors Affecting Stability:

• Nature of metal (charge, size, electronic configuration)

• Nature of ligand (size, charge, denticity)

• Geometrical constraints

Conceptual Focus: NEET often asks why chelates are more stable than monodentate complexes.

Applications of Coordination Compounds

1. Analytical Chemistry:

   • EDTA titrations for metal ions

   • [Fe(CN)₆]³⁻ and [Fe(CN)₆]⁴⁻ in redox reactions

2. Medicine:

   • Cisplatin ([Pt(NH₃)₂Cl₂]) → Anti-cancer drug

   • Vitamin B₁₂ (Cobalt complex) → Essential for metabolism

3. Industrial Applications:

   • Catalysis: [Ni(CO)₄], [V₂O₅] complexes

   • Colorants and dyes

NEET Focus: Conceptually link structure → properties → applications.

Quick Concept Summary Table

Conclusion

Coordination Chemistry is a crucial NEET Chemistry chapter. Conceptual understanding includes:

• Ligand types, coordination number, and geometry

• Bonding theories → VBT and CFT

• Isomerism and stability

• Applications in industry, medicine, and analytical chemistry

By linking structure → properties → applications, NEET aspirants can confidently tackle reasoning-based, application-oriented questions.

StudentBro.in provides structured, fully conceptual notes to help NEET aspirants master coordination chemistry efficiently, with H4 bold headings for readability and SEO optimization.