Ligand field theory and CuCl2 colors

In summary, Copper (II) chloride is a light brown solid that absorbs moisture to form a blue-green dihydrate. According to ligand field theory, the dihydrate form should have a larger d orbital splitting and a longer wavelength of color absorption compared to the anhydrous form. However, in this case, the opposite is observed. Possible explanations for this include charge-transfer transitions and the complex's lack of octahedral symmetry due to the arrangement of water and chlorine molecules.
  • #1
khanhhung2512
15
0
Copper (ii) chloride is a light brown solid, which slowly absorbs moisture to form a blue-green dihydrate.
According to ligand field theory, water is a stronger field ligand than chloride. As a result, the dihydrate form should have a larger d orbital splitting than the anhydrous form. Thus, the color (complementary to the wavelength absorbed) of the dihydrate form should have a longer wavelength than the anhydrous form's. But why is the opposite observed here?
If my reasoning is not correct, then please tell me the reason for the color change above.
Thank you very much.
 
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  • #2
Unless I am missing something, you got it wrong. Larger d orbital splitting means higher energy difference so a shorter wavelength.
 
  • #3
Well, the color we see is complementary to the color absorbed.
 
  • #4
There are a zillion of possible explanations.
There can be charge-transfer transitions invoved which have a much higher oscillator strength than the weak d-d transitions.
Also in the hydrated chloride there are two water molecules along the axis and four chlorines in the equatorial plane, so this complex doesn't have a symmetry octahedral symmetry.
 
  • #5
khanhhung2512 said:
Well, the color we see is complementary to the color absorbed.

That's what I missed
grumpy_borek.png
 
  • #6
These are two answers I found on the net http://answers.yahoo.com/question/index?qid=20110915202418AA2v9AN
While both answers seem wrong to me, one mentioned Advanced Inorganic Chemistry 6th ed (1999). p 868-869 (F. A. Cotton, G. Wilkinson, C. A. Murillo, M. Bochmann). If anyone has access to that book, please tell me what it really said.
Thanks.
PS: I only have access to the third edition of that book, so I don't know the corresponding pages.
 

What is ligand field theory?

Ligand field theory is a model that describes the bonding and electronic structure of transition metal complexes. It takes into account the interactions between the metal ion and the surrounding ligands, which can affect the color and other properties of the complex.

How does ligand field theory explain the colors of CuCl2?

In the case of CuCl2, the complex has a square planar geometry with two chloride ligands surrounding the central copper ion. The ligand field theory predicts that the d-orbitals of the copper ion will split into two sets, with the lower energy set being filled with electrons. The energy difference between these two sets corresponds to the energy of visible light, resulting in the absorption of certain wavelengths and the reflection of others, giving the complex its characteristic green color.

What factors influence the color of CuCl2?

The color of CuCl2 can be influenced by several factors, including the geometry and symmetry of the complex, the nature and number of ligands surrounding the central copper ion, and the strength of the ligand-field interactions. These factors can lead to different energy splittings and therefore different absorption and reflection of light, resulting in a range of possible colors for CuCl2 complexes.

How does ligand field theory relate to the spectroscopic properties of CuCl2?

Ligand field theory provides a framework for understanding the spectroscopic properties of CuCl2, such as its absorption and emission spectra. By considering the electronic structure and bonding in the complex, ligand field theory can predict the energies of transitions between different electronic states, which correspond to different colors and wavelengths of light.

Can ligand field theory be used to explain the colors of other transition metal complexes?

Yes, ligand field theory can be applied to a wide range of transition metal complexes, including those containing other metals besides copper. The theory takes into account the specific properties of each metal ion and ligand, allowing for a more comprehensive understanding of the colors and other properties of these complexes.

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