Coordination Compounds

Introduction

• D-block Elements: Metals like iron, copper, zinc often accept electron pairs instead of losing electrons.
  • Reasons:
    1. Empty shells allow accommodation of electron pairs.
    2. Completing the octet provides stability.
• Coordinate Bond: Formed when a neutral molecule like NH3 donates a pair of electrons to a metal atom (e.g., copper).
• Coordination Compounds: Complex compounds where a metal atom is bonded to ions/molecules.
  • Ligand: Molecule/ion donating an electron pair to a metal atom.

Basic Terms

• Central Atom: The metal atom in a coordination compound (e.g., chromium).
• Coordination Number: Number of electron pairs donated to the central atom.
• Coordination Sphere/Entity: Includes the central atom and all ligands within brackets.
• Counter Ion: Ions outside the coordination sphere.

Werner's Theory

• Coordination Compounds: First studied by Werner using cobalt chloride and NH3.
• Valencies:
  • Primary Valency: Satisfied by negative ions, indicates oxidation state, and is ionizable.
  • Secondary Valency: Satisfied by positive ions or neutral molecules, indicates coordination number, and is non-ionizable.
• Example Calculation: For cobalt, the primary valency is 3, and the secondary valency is 6.

Structure and Valencies

• Coordination compounds have structures based on primary and secondary valencies.
• Diagram examples show how ligands and counter ions arrange around the central metal atom.

Types of Ligands

• Density of a Ligand: Number of lone pairs donated.
• Types:
  1. Unidentate/Monodentate: Donates one pair (e.g., Cl⁻, Br⁻, CN⁻).
  2. Bidentate: Donates two pairs (e.g., ethane-1,2-diamine, oxalate).
  3. Ambidentate: Can donate from two different atoms (e.g., SCN).
  4. Polydentate: Donates many pairs (e.g., EDTA).

Complex Types

• Homoleptic: Central atom bonded to one type of ligand.
• Heteroleptic: Central atom bonded to multiple types of ligands.

Nomenclature

• Ligands classified by charge type: neutral, anionic, cationic.
• Rules:
  1. Name from left to right.
  2. Alphabetical order for multiple ligands.
  3. Use 'ATE' suffix for negative coordination spheres.

Crystal Field Theory (CFT)

• Splitting of d-Orbitals: When ligands approach, d-orbitals split based on ligand attack direction.
• Octahedral Complex: Ligands approach along axes, causing specific orbital energy changes.
• Tetrahedral Complex: Ligands approach between axes, causing opposite orbital energy changes.

Hybridization and VBT

• Example: Coordination compound of cobalt with NH3 shows D2sp3 hybridization.
• Geometry: Octahedral, based on orbital arrangements.
• Magnetic Properties:
  • Diamagnetic: If all electrons are paired.
  • Paramagnetic: If there are unpaired electrons.
• Magnetic Moment and Spin: Calculated using specific formulas based on electron configuration.

These notes provide a comprehensive overview of coordination compounds, their nomenclature, structure, and theories explaining their properties.