Q75P - Chemistry: Molecular Nature Of Matter And Change

Question

For any of the following that can exist as isomers, state the type of isomerism and draw the structures:

1. ^- $\left[\mathbf{PtCl}\mathbf{2}\mathbf{Br}\mathbf{2}\right]\mathbf{2}$
2. ^{-$\left[\mathbf{Cr}\left(\mathbf{NH}\mathbf{3}\right)\mathbf{5}\left(\mathbf{NO}\mathbf{2}\right)\right]\mathbf{2}$}
3. ^{-$\left[\mathbf{Pt}\left(\mathbf{NH}\mathbf{3}\right)\mathbf{4}\mathbf{I}\mathbf{2}\right]\mathbf{2}$}

Step-by-Step Solution

Answer

The 3 chemical structures given in the questions show isomerism. They exist as geometric (cis-trans) isomers and linkage isomers. 

 

^{$\left[\mathbf{PtCl}\mathbf{2}\mathbf{Br}\mathbf{2}\right]\mathbf{2}$-}geometric (cis-trans) isomerism 

 ^{$\left[\mathbf{Cr}\left(\mathbf{NH}\mathbf{3}\right)\mathbf{5}\left(\mathbf{NO}\mathbf{2}\right)\right]\mathbf{2}$}- linkage isomerism

^{$\left[\mathbf{Pt}\left(\mathbf{NH}\mathbf{3}\right)\mathbf{4}\mathbf{I}\mathbf{2}\right]\mathbf{2}$} - geometric (cis-trans) isomerism

Step 1: Concept Used – Isomerism

Definition of different kinds of isomers

 

Constitutional (structural) isomers – They have same formula, but  differently connected atoms; they can occur in two types:

 

Coordination isomers - They occur when the structure of the whole compound is the same, but the structure of complex ion is different

 

Linkage isomers - They occur when the structure of the complex ion is the    same, but the donor atom to which ligand  attached is different

 

Stereoisomers - They have the same connections between atoms, but the atoms have different spatial arrangements; they occur in two types:

 

geometric (cis-trans) isomers - different spatial arrangements of atoms or groups, relative to the central metal ion.

 

           2.2   Optical isomers - They occur when a molecule cannot be superimposed with its mirror image. 

Step 2: Elucidation of type of isomerism and structure

${\left[\mathrm{PtCl}2\mathrm{Br}2\right]}^{2-}$- Geometric (cis-trans) Isomerism

Step 3: Elucidation of type of isomerism and structure

${\left[\mathrm{Cr}\left(\mathrm{NH}3\right)5\left(\mathrm{NO}2\right)\right]}^{2-}$- Linkage Isomerism

Step 4: Elucidation of type of isomerism and structure

${\left[\mathrm{Pt}\left(\mathrm{NH}3\right)4\mathrm{I}2\right]}^{2-}$- Geometric (cis-trans) Isomerism