Ligand substitution reactions Flashcards
What are two similarly sized ligands?
H2O and NH3
What happens to the co-ordination number if the ligands are a similar size?
There will be no change
What ligand is larger than H2O and NH3?
Cl-
What happens to the co-ordination number when Cl- replaces H2O and NH3 in an octahedral complex?
Reduces from 6 to 4
What happens to the shape if the complex when Cl- replaces H2O and NH3 in an octahedral complex?
changes from octahedral to tetrahedral
What is a partial substitution of ligands?
Not all ligands are substituted for other ligands
What is haemoglobin?
A protein found in blood that helps to transport oxygen around the blood
What ions does haemoglobin contain?
Fe2+
What co-ordination number do the Fe2+ ions in haemoglobin have?
6
How many lone pairs does Fe2+ receive from nitrogen atoms?
4
What is porphyrin?
A multi dentate ligand which the 4 nitrogen atoms are a part of
Other than nitrogen, where do the other two lone pairs for the Fe2+ come from?
Globin (a protein)
Either an oxygen or a water molecule
What happens to haemoglobin in the lungs?
The oxygen concentration is high so water ligands are substituted for oxygen molecules to form oxyhaemoglobin
What happens to haemoglobin when it reaches the place where oxygen is needed?
The oxygen molecules are exchanged for water molecules
How is carbon monoxide poisonous?
The water and oxygen molecules are substituted for carbon monoxide ligands, forming carboxyhaemoglobin , meaning the haemoglobin can’t carry oxygen anymore
Which molecule binds most strongly to the iron, carbon monoxide, water or oxygen?
Carbon monoxide
what two things is complex ion stability affected by?
Enthalpy change
Entropy change
When is it hard for ligand exchange reactions to be reversed?
If the new complex is much more stable than the last
What type of ligand forms a more stable complex than mono dentate?
Multidentate and bidentate
How does enthalpy change during a ligand substitution reaction?
The enthalpy change is very small
Why is the enthalpy change during a ligand substitution the way it is?
The strengths of the bonds being broken is often very similar to the strength of the new bonds being made
What happens to the entropy when mono dentate ligands are substituted with multi dentate ligands? why?
Increases
Increases the number of particles
What is the chelate effect?
Multidentate ligands always forming much more stable complexes than mono dentate ligands
