Ligand substitution

• What is ligand substitution?

  Replacement of one ligand by another
• What happens during ligand substitution?

  New ligand formed is more stable
• Can ligands in a complex be replaced partially?

  Yes, they can be replaced partially or entirely
• What remains unchanged if n ligands are the same?

  No change in coordinate number or geometry
• What occurs when ligands of different sizes are involved?

  Change in coordination number and geometry
• What is the assumed form of transition element ions in solution?

  Hexaaqua complex with 6 water ligands
• What is the color of Cu2+(aq) complex?

  Blue
• What happens upon adding NaOH to Cu2+(aq)?

  Light blue precipitate forms
• What occurs during partial ligand substitution in Cu2+(aq)?

  2 water ligands replaced by 2 OH- ligands
• What happens when excess NH3 is added to Cu2+(aq)?

  Pale blue precipitate dissolves to deep blue solution

  
• What happens if concentrated NH3 is added dropwise to [Cu(H2O)6]2+?

  Light blue precipitate forms

  
• What occurs with excess ammonia solution after precipitate formation?

  Pale blue precipitate dissolves to deep blue solution

  
• What happens when chloride ligands replace water ligands in [Cu(H2O)6]2+?

  Blue solution turns yellow

  
• How does the coordination number change with chloride ligands?

  Changes from 6 to 4 due to size
• What is the geometry change when chloride ligands are added?

  Changes from octahedral to tetrahedral

  
• What happens when water is added to the yellow solution?

  Chloride ligands are displaced, returning to blue

  
• What color is the [Co(H2O)6]2+ complex?

  Pink
• What occurs upon adding NaOH to [Co(H2O)6]2+?

  Blue precipitate forms

  
• What happens with excess NaOH added to [Co(H2O)6]2+?


  Blue precipitate turns red when heated

  
• What happens when excess ammonia is added to [Co(H2O)6]2+?


  Brown solution forms

  
• What happens to cobalt (II) ion in air with ammonia ligands?

  Oxidized to cobalt (III), forming brown solution

  
• What occurs when chloride ligands replace water ligands in [Co(H2O)6]2+?

  Pink solution turns blue

  
• How does the coordination number change with chloride ligands in [Co(H2O)6]2+?

  Changes from 6 to 4 due to size
• What is the geometry change when chloride ligands are added to [Co(H2O)6]2+?

  Changes from octahedral to tetrahedral

  
• What happens when water is added to the blue solution of [CoCl4]2-?

  Chloride ligands are displaced, returning to pink

  
• What is the process of forming precipitates with transition metals?


  • Reaction with aqueous NaOH and NH3
  • Some precipitates dissolve in excess NaOH and NH3
• Cr3+ Aqua Ion

  Violet
• Cr3+ in OH-

  Pale Blue
• Cr3+ in Excess OH-


  Pale Blue Precipitate
• Cr3+ in NH3

  Pale Blue
• Cr3+ in Excess NH3

  Deep Blue