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    How does the size of a ligand affect the shape of the complex ion?
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    (Original post by Imsolost)
    How does the size of a ligand affect the shape of the complex ion?
    The answers to this could be pretty extensive.

    Complex ion shape is often more significantly effected by the strength of the ligand field, but you dont need to know about that.

    One example of ligand size having an effect is in Ni2+ complex ions. Here there are two effects that can be seen, firstly ligand size can change coordination number, secondly it can change co ordination geometry. (I must emphasise that there are other things influencing the shapes here, caused by how good or bad the ligands are at accepting or donating electrons, but these effects are beyond A level and size effects are still important.

    Ni(H2O)62+ is 6 co-ordinate, Octahedral

    Larger ligands make the central Nickel more crowded, hence the coordination number drops so

    Ni(Cl)42- is 4 co-ordinate, Tetrahedral.

    You may or may not know but transition metals dont obey VSEPR, and Ni2+ is in fact often found in a 4 coordinate square planar geometry!

    Ni(CN)42- is square planar, but if you change CN- for Cl-, one of the reasons it changes to tetrahedral geometry is because that relieves the strain between the bulky Cl- ligands that are close to one another!
 
 
 
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