Chemistry > Coordination Compounds > 10.0 Isomerism in Co-ordination compounds
Coordination Compounds
1.0 Basics
2.0 Addition Salt
3.0 Nomenclature of Co-ordination Compounds
4.0 Werner's Co-ordination Theory
5.0 Valence bond theory
6.0 Crystal field splitting theory (CFST)
7.0 Effective atomic number
8.0 Magnetic Moment
9.0 Application of Crystal Field Splitting Theory (CFST)
10.0 Isomerism in Co-ordination compounds
11.0 Organo-metallic compounds
12.0 Stability of Co-ordination compounds
10.1 Structural isomers
Structural isomers are divided in to five types:
1. Ionisation isomerism
2. Hydrate isomerism
3. Linkage isomerism
4. Ligand isomerism
5. Polymerisation isomerism
Ionisation isomerism: The coordination compounds having same molecular formula but different ions on the ionization are called IONIZATION ISOMERS.
Example:
With $AgN{O_3}$ red violet gives white ppt of $AgS{O_4}$
$$\left[ {Co{{(N{H_3})}_5}Br} \right]S{O_4} \to {\left[ {Co{{(N{H_3})}_5}Br} \right]^{ + 2}} + SO_4^{ - 2}$$
With $AgN{O_3}$ pale yellow $AgBr$
$$\left[ {Co{{(N{H_3})}_5}S{O_4}} \right]Br \to {\left[ {Co{{(N{H_3})}_5}S{O_4}} \right]^ + } + B{r^ - }$$
Hydrated isomerism: The coordination compounds having same molecular formula but produce different number of molecule on ionisation.
Example:
$\left[ {Cr{{({H_2}O)}_6}} \right]C{l_3} \to {\left[ {Cr{{({H_2}O)}_6}} \right]^{3 + }} + 3C{l^ - }$
violet
$\left[ {Cr{{({H_2}O)}_5}Cl} \right]C{l_2}.{H_2}O \to {\left[ {Cr{{({H_2}O)}_5}Cl} \right]^{ + 2}} + 2C{l^ - } + {H_2}O$
yellow -green
$\left[ {Cr{{({H_2}O)}_4}C{l_2}} \right]Cl.2{H_2}O \to {\left[ {Cr{{({H_2}O)}_4}C{l_2}} \right]^ + } + C{l^ - } + 2{H_2}O$
dark -green
Linkage isomerism: This type of isomerism is observed when the coordination compound having same molecular formula and amidentate ligand.
Example: $\left[ {Co{{(N{H_3})}_5}N{O_2}} \right]C{l_2}$ $\left[ {Co{{(N{H_3})}_5}(ONO)} \right]Cl$
Co-ordination isomerism: This type of isomerism is observed in the coordination compounds in which both cation and anion are complex ions and the isomerism arises due to exchange of ligand.
Example: $\left[ {Cr{{(N{H_3})}_6}} \right]\left[ {Cr{{(CN)}_6}} \right]$
$\left[ {Cr{{(N{H_3})}_5}{{(CN)}_2}} \right]\left[ {Cr{{(CN)}_5}N{H_3}} \right]$
$\left[ {Cr{{(N{H_3})}_4}{{(CN)}_2}} \right]\left[ {Cr{{(CN)}_4}{{(N{H_3})}_2}} \right]$
$\left[ {Cr{{(N{H_3})}_3}{{(CN)}_3}} \right]\left[ {Cr{{(CN)}_3}{{(N{H_3})}_3}} \right]$ =This does not exist .
2) $\left[ {Cu{{(N{H_3})}_4}} \right]\left[ {PtC{l_4}} \right]$
$\left[ {Cu{{(N{H_3})}_3}Cl} \right]\left[ {Pt(N{H_3})C{l_3}} \right]$
$\left[ {Cu{{(N{H_3})}_2}C{l_2}} \right]\left[ {Pt{{(N{H_3})}_2}C{l_2}} \right]$ = this does not exist.
$\left[ {Cu(N{H_3})C{l_3}} \right]\left[ {Pt{{(N{H_3})}_3}Cl} \right]$ = $\left[ {Pt{{(N{H_3})}_3}Cl} \right]\left[ {Cu(N{H_3})C{l_3}} \right]$
$\left[ {Pt{{(N{H_3})}_3}Cl} \right]\left[ {Cu(N{H_3})C{l_3}} \right]$ = $\left[ {Pt{{(N{H_3})}_4}} \right]\left[ {CuC{l_4}} \right]$
Ligand isomerism: The compound having the same molecular formula differ due to the isomerism in the ligands.
Example:
${\left[ {Co{{(Pn)}_3}} \right]^{ + 3}} and {\left[ {Co{{(tn)}_3}} \right]^{ + 3}}$ are ligand isomers.
Polymerisation isomerism: This is not true isomerism because it occurs between compounds have same empirical formula, but different molecular weights. The molecular weights, molecular composition are simple multiples of stoichiometric arrangement.
Example: In the following three compounds the $2^{nd}$ and $3^{rd}$ compounds are polymers of the first $\left[ {Pt{{(N{H_3})}_2}C{l_2}} \right],\left[ {Pt{{(N{H_3})}_4}} \right]\left[ {PtC{l_4}} \right],\left[ {Pt{{(N{H_3})}_4}} \right]\left[ {Pt(N{H_3})C{l_3}} \right]$
