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Chemistry 2

Complex Formation and Ligands

takriban dakika 8 kusoma

Mada za sehemu hiiTransition ElementsMada 2
  1. Characteristics of Transition Elements
  2. Complex Formation and Ligands

Complex compounds

A complex compound consists of a central metal atom or ion and several ligands. The central atom typically has vacant orbitals that accommodate pairs of electrons from the ligands. Transition metals are known for forming complex compounds due to their ability to accommodate these electrons.

Examples of central atoms and the number of ligands they accommodate:

  • Ag⁺ – 2
  • Hg²⁺ – 4
  • Al³⁺ – 4
  • Zn³⁺ – 4
  • Pb²⁺ – 4
  • Cu²⁺ – 4
  • Cr³⁺ – 6
  • Mn²⁺ – 5/6
  • Fe²⁺/Fe³⁺ – 4/6
  • Ni²⁺ – 4/6
  • Co²⁺ – 4/5
  • Pb²⁺ – 4/6

A ligand is a non-metallic ion or molecule that donates a pair of electrons to the central metal atom/ion during complex compound/ion formation. These non-metallic ions or molecules have a pair of electrons in their valency orbital, which are called lone pairs.

Types of ligands

Neutral ligand

A neutral ligand is electrically neutral and does not carry a charge. These ligands are generally molecular species with one or more lone pairs of electrons.

  1. Example: Amine (NH₃)
  2. Example: Aqua (H₂O)
  3. Example: Carbonyl (CO)
  4. Example: Ethane-1,2-diamine (NH₂-CH₂-NH₂)

Anionic ligands

Anionic ligands carry a negative charge. These include:

  • Fluoro (F⁻)
  • Chloro (Cl⁻)
  • Iodo (I⁻)
  • Cyano (CN⁻)
  • Hydroxo (OH⁻)
  • Nitro (NO₂⁻)
  • Nitrate (NO₃⁻)
  • Carbonate (CO₃²⁻)
  • Sulphate (SO₄²⁻)
  • Oxalato (C₂O₄²⁻)

Anionic ligands generally form anionic complex ions, such as [AgCl₂]⁻, [Pb(CN)₄]²⁻, [Fe(CN)₆]⁴⁻, [Ag(CN)₂]⁻.

Classification based on mode of attachment

  1. Monodentate (Unidentate) Ligands: Ligands that attach to the central metal atom/ion through one point.
  2. Bidentate Ligands: Ligands that attach to the metal ion through two points.
  3. Tridentate Ligands: Ligands that attach to the metal ion through three points.
  4. Tetradentate Ligands: Ligands that attach through four points.
  5. Pentadentate Ligands: Ligands that attach through five points.
NeutralAnionicAnionic
H₂O - AquaF⁻ (Fluorido)OH⁻ (hydroxo)
NH₃ - ammineCl⁻ (chlorido)HS⁻
CO - carbonylBr⁻ (Bromido)O²⁻ Oxo
NO - NitrosylI⁻ (Iodido)S²⁻
C₅H₅NH⁻O₂²⁻ Peroxo
NH₂-NH₂CN⁻ CyanoNO₃²⁻ (Nitrato)
CH₃COO⁻ acetateONO⁻
SCN⁻ thiocyanatoC₂O₄²⁻ (oxalate)
NCS⁻ isothiocyanatoCO₃²⁻ (carbonate)
NO₂⁻ (Nitro)

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