What are axial ligands?

  1. In this article:
    http://jredman.kombyonyx.com/thesis/Ch16.htm
    they mention "axial ligands" and "peripheral ligands". What exactly does that mean? Heres the molecule they use as an example:
    [​IMG]
    I can see that the porphyrin rings both have a metal ligand M binded to them. That oxygen atom which bridges the two M ligands, is that an "axial ligand"? Is it even a ligand at all, I thought a ligand meant an electrophilic species which accepts electrons from an electron doner and forms a dative bond. I'm used to oxygen atoms being an electron doner.
     
  2. jcsd
  3. Axial and peripheral refer to the positions in complexes displaying geometries like that of trigonal bipyramidal or octahedral. In the former case you can think of three ligands which make up the "base" of each pyramid as equatorial/peripheral and the two other ligands as the axial. The same idea is applied to octahedral complexes, notice the pyrrole nitrogen a are equatorial and with the bridging O being axial in both metals (so is the thing at the very top but my phone wont show me the full size picture).
     
  4. That explains it, thanks a lot.
     
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