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Homework Help: How do you know the order of ligands?

  1. Sep 17, 2016 #1
    1. The problem statement, all variables and given/known data
    So i have triammineaquadihydroxochromium(III) chloride and i have to write the formula.

    2. Relevant equations

    3. The attempt at a solution
    So theres (NH3)3, H2O, (OH)2, Cr and a Cl anion

    I know the transition metal goes first, and the charge of the complex is 1+ so it'll be = {Cr - - - ] Cl

    But now how do i know what order to put the (NH3)3, H2O, (OH)2? I don't think it has to be alphabetical. If it is alphabetical then this is simple. And it cant just be put the metal, then the neutral ligands then charged ligand because there are two neutral ligands, (NH3)3 and H2O, so which one of those would go first...
    Last edited: Sep 17, 2016
  2. jcsd
  3. Sep 17, 2016 #2
    so i think i found out how to do it, neutrals should come before charged ligands, and neutrals should be organized alphabetically according to chemical symbol, not name.

    So this will be [CrH2O(NH3)3(OH)2]Cl

    But im really not too sure, i see so many complexes that have the metal then a negatively charged ligand then the neutral. Like [CrCl2(H2O)4]
    Last edited: Sep 17, 2016
  4. Sep 18, 2016 #3


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    Staff: Mentor

    TBH I am not sure what the correct answer ism but the only authoritative source on that will be one of the IUPAC books defining naming rules. Quick googling suggests it is a so called "Red book".
  5. Sep 19, 2016 #4

    Dr Uma Sharma

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    Gold Member

    As IUPAC Rule
    First is always Cation and then anion
    In your example cation is a complex and anion is Cl-
    triammineaquadihydroxochromium(III) ...Now here first write the Transition metal (Cr) ,then anionic ligand (2OH-) and then neutral ligand alphabetically (first H2O and then NH3 )
    So The answer is [Cr(OH)2(H2O)(NH3)3]Cl
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