[Wuffe_devil]

Hello!

We have recently done an experiment on five Cu complexes [Cu(H2O)n(NH3)6-n]2+ and acquired their spectra, and the influence of ligand field strength was observed based on the spectra results.

So, as far as I know, NH3 is a stronger field ligand, meaning the energy goes up as number of n(number of water molecules) go down, and this was observed in our results, however for [Cu(H2O)2(NH3)4]2+ seems to have higher energy than [Cu(H2O)(NH3)5]2+ and i cant seem to find a reason why... I'm not sure how this could be explained using ligand field theory either.

Any advice would be greatly appreciated.

[UG]

 I believe the answer is to do with the Jahn-Teller distortion of the d⁹ copper complex. The six metal-ligand bonds are not of equal length.

[Wuffe_devil]

I believe the answer is to do with the Jahn-Teller distortion of the d⁹ copper complex. The six metal-ligand bonds are not of equal length.

Hmm? I knew that but I am not sure how this is connected to this.

I know that Jahn-Teller distortion will make the octahedral molecule acquire tetragonal geometry and the bond lengths will be different. But that applies for all the 5 compounds right? why is [Cu(H2O)(NH3)5]2+ different? I'm not quite sure what makes this ion different from the others

[UG]

There are 4 short C-N bonds in [Cu(H₂O)₂(NH₃)₄]²⁺ and 2 long C-O bonds. Adding another ammonia ligand forces the formation of another long C-N replacing the long C-O bond. Is this favourable?

[Wuffe_devil]

There are 4 short C-N bonds in [Cu(H₂O)₂(NH₃)₄]²⁺ and 2 long C-O bonds. Adding another ammonia ligand forces the formation of another long C-N replacing the long C-O bond. Is this favourable?

Oh I see, thanks for clarification!

[grs35]

There are 4 short C-N bonds in [Cu(H₂O)₂(NH₃)₄]²⁺ and 2 long C-O bonds. Adding another ammonia ligand forces the formation of another long C-N replacing the long C-O bond. Is this favourable?

What C-O and C-N bonds are you talking about ?

[UG]

Oops I meant Cu-O and Cu-N bonds