Ligands (Edexcel International A Level (IAL) Chemistry): Revision Note

Monodentate ligands

• Monodentate ligands can form only one dative bond to the central metal ion 

• This is because they donate only one 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 & Multidentate 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 central metal ion 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