Ligands (Edexcel International A Level Chemistry)

• Monodentate ligands can form only one dative bond to the central metal ion 
• This is because they have a single lone pair of electrons to form a dative bond with the 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-diaminoethane (H₂NCH₂CH₂NH₂) which is also written as ‘en’
  • Ethanedioate ion (C₂O₄^2- ) which is sometimes written as ‘ox’

Examples of complexes with bidentate ligands

Multidentate 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 multidentate ligands
• An example of a multidentate 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