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Why is potassium permanganate coloured?

  1. Oct 11, 2011 #1
    In the permanganate ion, manganese is in the +7 oxidation state, therefore it is a d0 ion. I thought that d0 and d10 ions don't absorb visible spectrum radiation because there are no electrons to jump to higher crystal field orbitals (or in the case of d10 ions, there are no free orbitals for electrons to jump to). I remember reading months ago an explanation for this that involved something to do with the ligand donating electrons into Mn(VII)s empty d orbitals. Can anyone explain this to me?

    EDIT: Also I'd like to know why chromate is coloured. Again Cr(VI) is a d0 ion, therefore its not absorbing radiation due to electrons jumping to higher orbitals in the crystal field. What is causing it to absorb visible radiation?

    UPDATE: I found out the answer to this question. Permanganate, chromate and dichromate are coloured for the same reason. Ligand to metal charge transfers. In each case, oxygen transfers electrons to the empty d orbitals on the metal atom. Interesting stuff, I found this info here:
    http://www.webexhibits.org/causesofcolor/8.html
     
    Last edited: Oct 11, 2011
  2. jcsd
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