• A?ligand?is a molecule or ion that has?one?or?more?lone pairs of electrons
• These lone pairs of electrons are donated by the ligand, to form?dative covalent bonds?to a central metal atom or ion

Examples of ligands table

Example of a complex formed between a transition metal ion (Fe²⁺) and a ligand (H₂O) by dative covalent bonds

• Different?ligands?can form different numbers of dative bonds to the central metal ion in a complex.
  • Some ligands can form?one?dative bond to the central metal ion
  • Other ligands can form?two?dative bonds, and some can form?multiple?dative bonds

Monodentate ligands

• Monodentate?ligands can form only?one?dative bond to the central metal ion
• Examples of monodentate ligands are:
  • Water (H₂O) molecules
  • Ammonia (NH₃) molecules
  • Chloride (Cl^-) ions
  • Cyanide (CN^-) ions

Examples of complexes with monodentate ligands

Bidentate ligands

• Bidentate?ligands can each form?two?dative bonds to the central metal ion
• This is because each ligand contains?two?atoms with lone pairs of electrons
• Examples of bidentate ligands are:
  • 1,2-iaminoethane (H₂NCH₂CH₂NH₂) which is also written as?‘en’
  • Ethanedioate ion (C₂O₄^2-?) which is sometimes written as?‘ox’

Examples of complexes with bidentate ligands

Polydentate ligands

• Some ligands contain more than two atoms with lone pairs of electrons
• These ligands can form more than two dative bonds to the and are said to be?polydentate?ligands
• An example of a polydentate ligand is EDTA^4-?, which is a?hexadentate?ligand as it forms 6 dative covalent bonds to the central metal ion

Example of a polydentate ligand complex