Coordination Compounds

Introduction

• Coordination Compounds: Complex compounds where a metal atom is bonded to ions or molecules by accepting pairs of electrons.
• Metal Elements: D-block elements like iron, copper, zinc.
  • Usually lose electrons.
  • In coordination compounds, metals accept electron pairs due to:
    1. Empty shells.
    2. Completing the octet rule for stability.

Formation of Coordination Compounds

• Example: Metal atom (e.g., Copper) with a neutral molecule (e.g., NH3).
  • Copper accepts electron pair from NH3 (donor with lone pair on N), forming a coordinate bond.
  • Ligand: Ion/molecule donating electron pair (e.g., NH3).
• Parts of Coordination Compound:
  1. Metal atom (e.g., Copper).
  2. Ligand (e.g., NH3).

Basic Terms

• Central Atom: Metal atom (e.g., Chromium in Cr(NH3)6Cl3).
• Coordination Number: Number of electron pairs donated (e.g., 6 for NH3 ligands).
• Coordination Sphere/Entity: Part in square brackets (e.g., [Cr(NH3)6]).
• Counter Ion: Ion outside the coordination sphere (e.g., Cl-).

Werner's Theory

• Werner's Studies: First to study coordination compounds; highlighted primary and secondary valencies.
• Valencies:
  • Primary Valency: Related to oxidation state, ionizable (e.g., Cl-).
  • Secondary Valency: Related to coordination number, non-ionizable (e.g., NH3).

Valency Calculation

• Primary Valency: Equals oxidation number.
• Secondary Valency: Equals coordination number.

Types of Ligands

• Denticity: Number of electron pairs a ligand donates.
  • Unidentate: Donates one pair (e.g., Cl-, CN-).
  • Bidentate: Donates two pairs (e.g., ethylenediamine, oxalate).
  • Ambidentate: Two potential donor atoms (e.g., SCN-).
  • Polydentate: Donates multiple pairs (e.g., EDTA).

Complex Types

• Homoleptic Complex: One type of ligand.
• Heteroleptic Complex: More than one type of ligand.

Nomenclature

• Ligand Names:
  • Neutral: NH3, H2O.
  • Anionic: Chloro, Bromo (suffix 'o').
  • Cationic: Nitronium, Hydroxonium (suffix 'ium').
• Naming Rules:
  1. Name from left to right.
  2. Alphabetical order for multiple ligands.
  3. 'ate' suffix for negative coordination spheres.

Crystal Field Theory (CFT)

• Concept: Explains splitting of d orbitals when ligands approach.
• Octahedral Complexes:
  • Splitting: d_xy, d_yz, d_xz (T2g) lower energy; d_x²-y², d_z² (Eg) higher energy.
• Tetrahedral Complexes:
  • Splitting: d_xy, d_yz, d_xz (T2) higher energy; d_x²-y², d_z² (E) lower energy.

Valence Bond Theory (VBT) and Hybridization

• Hybridization: Involves mixing of orbitals (e.g., d²sp³ for octahedral complexes).
• Magnetic Properties:
  • Diamagnetic: All electrons paired.
  • Paramagnetic: Presence of unpaired electrons.

Measurement

• Magnetic Moment: μ = √n(n+2), where n is number of unpaired electrons.
• Spin Multiplicity: 2S + 1, where S is the spin quantum number.

These notes summarize the essential concepts and terminologies from the chapter on coordination compounds, encompassing the formation, types, nomenclature, and theoretical explanations.