Structural Isomerism

Before discussing about this topic please go through the link  and get idea about isomerism .

Classification of  Structural isomerism:

1.Ionisation isomerism:

  • In these isomer there is exchange of ligand between coordination sphere and ionization sphere.
  • Here the chemical formula is same, only the ligands present inside and outside the coordination sphere are exchanged.
  • These isomers give different ions when dissolved in water.
  • For example
    [Co(NH3)5Br]SO4   and [Co(NH3)5SO4  ]Br  and show ionization isomerism. Here we noticed that in both the compound only sulphate ion and bromide ion are among themselves.
  • Some other examples are  ,
    [Co(NH3)5Cl]SO4   and   [Co(NH3)5SO4]Cl 
    [Co(NH3)5NO3]SO4   and   [Co(NH3)5SO4]NO3 
    [Co(en)2Cl(NO2)]SCN   and   [Co(en)2Cl(SCN)]NO2 

2.Hydrate isomerism:

  • Hydrate means the word water, so in this type of isomerism only the water molecule is exchanged between coordination sphere and ionization sphere.
  • When we dissolve these isomers in aqueous solution, they give different colour.
  • For example,

    [Cr(H2O)6]Cl3 (violet)    and    [Cr(H2O)5Cl]Cl2.H2O (pale, green)
  •  Here we all notice one thing that, number of water and chlorine molecule is same    in both the  compound. The only difference is that in 1st compound all the water molecule is present inside the coordination sphere but in second one five is present inside and one is present outside the  coordination sphere.

3.Linkage isomerism: 

  • Linkage isomerism is shown by ambidentate ligand(ligand that have two different donor atom).
  • Linkage isomerism arises when an ambidentate ligand can coordinate to a metal cation through either of the two donor atoms.
  • Lets take an ambidentate ligand

    NO2  ion, it has two donor atom N-atom and  O-atom, it can coordinate to the metal cation either through nitrogen atom or through oxygen atom.
  • The linkage isomers containing NO2 as ligand are

               [Co(NH3)5(NO2)]2+     ( N-atom coordinate to Co3+ )
       and  [Co(NH3)5(ONO)]2+    ( O-atom coordinate to  Co3+ )

4.Coordination isomerism:

  • The compound in which both cation and anion are complex ions and there nay be exchange of ligands between these two complex ions are known as coordination isomer.
  • In the pairs of these isomers,the central metal cation in the two coordination sphere may be same or different.
  • Some examples are 

    [Co(NH3)6][Cr(CN)6]    and      [Cr(NH3)6][Co(CN)6]

    [Cu(NH3)4][PtCl4]     and     [Pt(NH3)4][CuCl4] 

5. Coordination position isomerism:

  • This type of isomerism is formed by the bridging complex and there is a exchange of ligand between two metal cations.
  • For example,

2098_Coordination Position Isomerism.png

  •  Here we can see that only ligands are exchange in between the coordination so here and ionization sphere.

6. Ligand isomerism: 

  • If the ligand itself exist in two or more isomeric form, then the complexes containing such type of ligand show ligand isomerism.
  • For exampleCH3 – CH – CH2         and       CH3 – CH – CH2              
                                     |         |                            |                    |
                                   NH2   NH2                        NH2                 NH2
                                1,2-diaminopropane        1,3-diaminopropane

     Here we see that only the ligands are exchanged their position in order to show ligand isomerism.

7. Polymerization isomerism:

  • Polymers are not real isomers.
  • These type of isomers have same emperical formula but different molecular formula.
  • All these isomers have same ratio of metal atoms and ligands in them.
  • Coordintion polymers of Pt2 ion:
    Complex compound
    Number of  Pt2+
    Number of  NH3
    Number of  Cl

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