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Ligand exchange of copper (ii)

When you add excess ammonia to hydrated copper ii ion, it goes to [Cu(NH3)4(H2O)2]2+


Why doesn't it go to [Cu(NH3)6]2+ instead?

Any help is appreciated. Thanks a lot.
Original post by caddy5384
When you add excess ammonia to hydrated copper ii ion, it goes to [Cu(NH3)4(H2O)2]2+


Why doesn't it go to [Cu(NH3)6]2+ instead?

Any help is appreciated. Thanks a lot.


There is more than one factor involved here. But is basically comes down to stability.

1. Ammonia molecules are larger than water molecules. This makes octahedral occupation more strained.

2. You are still operating in aqueous solution and there is an excess of water molecules. There are two sites on the octahedral complex that are longer than the others, the axial sites. This is down to an effect called Jahn -Teller. It makes the axial sites more labile (easier to exchange ligands). As these ligands are easily exchanged the most likely occupation is water.

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