Ligand Substitution Flashcards
Ligand substitution reaction
Where in a transition metal ion complex, one ligand replaces another ligand
When a new complex is formed what happens?
A colour change
What does the specific colour change in a ligand substitution reaction depend on?
The position of equilibrium of the ligand substitution reaction
Depends on the relative concentration of the different complex metal ions in reactant or product
Can a coordination number change happen in this reaction?
Yes
Complex of copper ions (in copper sulfate) when hydrated in water formula
[Cu(H₂O)₆ ²⁺
Aka 6 water in an octahedral complex ion surrounds Cu2+ ion
What colour is [Cu(H₂O)₆]²⁺ (copper 2 sulfate in water)?
Pale blue
Initial reaction on addition of 2NH3 to [Cu(H₂O)₆ ²⁺
Forms [Cu(H₂O)₄(OH)₂] and 2NH4+
Observations for initial reaction of addition of NH3 ammonia to [Cu(H₂O)₆ ²⁺
Colour change pale blue solution forms a pale blue precipitate
What type of reaction is formation of [Cu(H₂O)₄(OH)₂]? (In first step of addition of 2 NH3 to aqua copper complex)
Acid base reaction where NH3 acts as a base to remove H+ from 2 water ligands
So 2 water ligands become OH-
Why does [Cu(H₂O)₄(OH)₂] precipitate out of solution to form a pale blue precipitate?
Because the 2 OH- ligands cancel out the Cu2+ charge so overall is a neutral complex
So cannot dissolve in polar charged water
What is formed When more NH3 is added to [Cu(H₂O)₄(OH)₂]
Forms [Cu(NH3)4(H2O)2]2+ and water and OH-
What type of reaction is formation of [Cu(NH3)4(H2O)2]2+ from [Cu(H₂O)₄(OH)₂] when more ammonia is added
Ligand substitution because 4 NH3 acts as ligands and substitute the 2 OH- and 2 H2O ligands
Observation for formation of [Cu(NH3)4(H2O)2]2+ from ammonia?
The pale blue precipitate redissolves and forms a dark blue solution
Why does [Cu(NH3)4(H2O)2]2+ redissolve?
Because it is charged so can attract polar water molecules and so dissolve
Change in coordination of ammonia + hexaaqua copper complex?
None: all complexes are octahedral with 6 ligands bonded
