Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Ligand field theory and CuCl2 colors

  1. Nov 28, 2013 #1
    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.
     
  2. jcsd
  3. Nov 28, 2013 #2

    Borek

    User Avatar

    Staff: Mentor

    Unless I am missing something, you got it wrong. Larger d orbital splitting means higher energy difference so a shorter wavelength.
     
  4. Nov 28, 2013 #3
    Well, the color we see is complementary to the color absorbed.
     
  5. Nov 28, 2013 #4

    DrDu

    User Avatar
    Science Advisor

    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.
     
  6. Nov 28, 2013 #5

    Borek

    User Avatar

    Staff: Mentor

    That's what I missed [​IMG]
     
  7. Nov 28, 2013 #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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Ligand field theory and CuCl2 colors
  1. Crystal Field Theory (Replies: 1)

Loading...