substitution recations

• what happens when ligands of a similar size and the same charge are swapped? give an example

  the coordination number doesn't change and the shape doesn't change, only the colour changes

  
  

  [Co(H2O)6]2+ + 6NH3 -> [Co(NH3)6]2+ + 6H2O

  
  

  pink straw coloured
• give an example of when there is only partial substitution?

  [Cu(H2O)6]2+ + 4NH3 -> [Cu(NH)3(H2O)2]2+ + 4H2O

  Blue deep blue
• what happens when ligands of different sizes are substituted for each other? give examples

  the coordination number changes and the shape changes

  [Co(H2O)6]2+ + 4Cl- -> [CoCl4]2- + 6H2O

  octahedral (pink) tetrahedral (blue)

  [Cu(H2O)6]2+ + 4Cl- -> [CuCl4]2- + 6H2O

  octahedral (pale blue) tetrahedral (yellow)

  [Fe( H2O)6]3+ + 4Cl- -> [FeCl4]- + 6H2O

  octahedral (yellow) tetrahedral (yellow)
• do different ligands have different bond strengths?

  yes
• when can't ligand substitutions be reversed?

  when the new complex is more stable than the old one
• give an example when the new complex ion is more stable so can't be reversed?


  [Fe(H2O)6]3+ + 6CN- -> [Fe(CN)6]3- + 6H2O
• do multidentate ligands form more stable complexes than mondentate ligands? give an example

  yes

  [Cu(H2O)6]2+ + 3NH2CH2CH2NH2 -> [Cu(NH2CH2CH2NH2)3]2+ + 6H2O
• what makes a more stable complex?

  a positive entropy change
• why is the enthalpy change very small for ligand exchange?

  as the strength of the bonds broken is often very similar to the strength of the new bonds being made
• what is the increase in stability in multidentate ligands known as? and explain this effect

  it is known as the chelate effect.

  when monodentate ligands are substituted with bidentate or multidentate ligands, the number of particles in solution increases. The more particles, the greater the entropy. Reactions that result in an increase entropy are more likely to occur.
• what would happen when reversing ligand substitution?

  entropy would decrease