Coordination Compounds

Introduction

D Block Elements: Iron, copper, zinc, etc., are metals.
- Metals usually lose electrons but in coordination compounds, they accept a pair of electrons.
Reasons for metal electron acceptance:
- Empty shells
- Completing the octet rule for stability
Example: Copper (Cu) and ammonia (NH3)
- Cu has an empty shell and NH3 has a lone pair of electrons.
- NH3 donates electrons to Cu → forming a coordinate bond → a coordination compound.

Complex compounds where a metal atom is bonded to ions or molecules.
Ligand: An ion/molecule that donates a pair of electrons to a central metal atom.

Central Atom: The main metal atom in the coordination compound (e.g., Chromium).
Ligand: Example - NH3 donating a pair of electrons.
Coordination Number: Number of electron pairs donated (e.g., in [Cr(NH3)6]Cl3, NH3 donates 6 pairs).
Coordination Sphere/Entity: The central atom and its surrounding ligands within square brackets.
Counter Ion: Ion outside the coordination sphere (e.g., Cl in [Cr(NH3)6]Cl3).

Werner's experiments with cobalt chloride and NH3 led to cobalt chloride.6 NH3.
Key Findings:
- 6 NH3 are directly bonded to the Co atom (secondary valency)
- 3 Cl are indirectly bonded (primary valency)
Conclusions:
- Primary Valency: Satisfied by negative ions (e.g., Cl).
  - Represents oxidation state, denoted by dots, ionizable.
- Secondary Valency: Satisfied by positive ions or neutral molecules (e.g., NH3).
  - Represents coordination number, denoted by lines, non-ionizable.

Example 1: [Co(NH3)6]Cl3
- Primary valency = Oxidation number (Co = +3).
- Secondary valency = Coordination number (6 ligands).
Example 2: [Fe(CN)6]4-
- Primary valency = Oxidation number (Fe = +2).
- Secondary valency = Coordination number (6 ligands).

Using octahedral geometry, illustrating valencies and positions of ligands and counter ions.
Exploring structures like [Co(NH3)6]3+, [Co(NH3)5Cl]2+, etc.

Denticity: Number of lone pairs donated to the central metal.
Types:
- Unidentate: One pair (e.g., Cl-, CN-).
- Bidentate: Two pairs (e.g., ethylenediamine 'en').
- Ambidentate: Different atoms donate (e.g., SCN-).
- Polydentate: Multiple pairs (e.g., EDTA).

Rules:
1. Ligands listed alphabetically.
2. Prefixes used to denote the number (e.g., di-, tri-).
3. If anionic, suffix '-ate' is added to the metal.
Examples:
- [Ag(NH3)2]Cl: Diamminesilver(I) chloride.
- [K2NiCl4]: Potassium tetrachloronickelate(II).

Concept: Describes D orbital splitting when ligands approach a metal ion.
- Octahedral: Ligands approach along axes, increasing energy of d(x^2-y^2) and d(z^2).
- Tetrahedral: Ligands approach between axes, increasing energy of d(xy), d(yz), and d(xz).
Impact: Causes different arrangements in electron levels; influences properties like color, magnetism.

Octahedral: Splitting into higher energy (e_g) and lower energy (t_2g).
- Energy levels: e_g (+0.6Δ) and t_2g (-0.4Δ)
Tetrahedral: Opposite splitting.
- Energy levels: T_2 (+0.4Δ) and E (-0.6Δ)

Determining structure, magnetic properties, and spin states using electron configurations and ligand strength.
Method: Calculate oxidation state, determine electron arrangement.
- Example: [Co(NH3)6]3+
  - Oxidation state of Co = +3
  - Strong ligand NH3 causes pairing.
  - Hybridization yields D2SP3 (octahedral geometry, diamagnetic).

Metal atoms in coordination compounds accept electrons to gain stability.
Coordination compounds consist of metal centers and ligands forming coordinate bonds.
Werner's theory introduces primary and secondary valencies, explaining metal-ligand bonding.
Ligands categorized by denticity and impact on metal centers differ across coordination complexes.
Crystal Field Theory elaborates on D orbital interactions with ligands, affecting compound properties.
Valence Bond Theory aids in understanding coordination compound structure, hybridization, and magnetic behavior.