Substitution Reactions

H2O, NH3 and Cl− can act as monodentate ligands.

The ligands NH3 and H2O are similar in size and are uncharged.

Exchange of the ligands NH3 and H2O occurs without change of co-ordination number (eg Co2+ and Cu2+).

Substitution may be incomplete (eg the formation of [Cu(NH3)4(H2O)2]2+).

The Cl− ligand is larger than the uncharged ligands NH3 and H2O

Exchange of the ligand H2O by Cl– can involve a change of co-ordination number (eg Co2+, Cu2+ and Fe3+).

Ligands can be bidentate (eg H2NCH2CH2NH2 and C2O42–).

Ligands can be multidentate (eg EDTA4–).

Haem is an iron(II) complex with a multidentate ligand.

Oxygen forms a co-ordinate bond to Fe(II) in haemoglobin, enabling oxygen to be transported in the blood.

Carbon monoxide is toxic because it replaces oxygen co-ordinately bonded to Fe(II) in haemoglobin.

Bidentate and multidentate ligands replace monodentate ligands from complexes. This is called the chelate effect.