Question

Which one of the following has the largest number of isomers? ( R= Alkyl group, en = Ethylenediamine)

• A. ${\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]}^{+}$
• B. ${\left[\mathrm{Ru}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Cl}\right]}^{2+}$
• C. ${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Cl}\right]}^{2+}$
• D. ${\left[\mathrm{Ir}{\left({\mathrm{Pr}}_3\right)}_2\mathrm{H}\left(\mathrm{CO}\right)\right]}^{2+}$

Answer 1

The correct option is A

${\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]}^{+}$

The explanation for the correct option

(A) ${\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]}^{\mathbf{+}}$

Isomerism

• Isomerism is the phenomenon when two or more chemical compounds have the same chemical formula but distinct chemical structures.
• Stereoisomerism and structural isomerism are the two types of isomerism.
• Stereoisomerism is classified as Ionization isomerism, hydration isomerism, coordination isomerism, ligand isomerism, and linkage isomerism.
• Geometrical isomerism and optical isomerism are two types of stereoisomerism.

Dichloridobis(ethane-1,2-diamine) Cobalt (III)

• ${\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]}^{+}$ (Dichloridobis(ethane-1,2-diamine) Cobalt (III)) show geometrical as well as optical isomerism.
• Therefore, it has the largest number of isomers.

The explanation for incorrect options

(B) ${\left[\mathrm{Ru}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Cl}\right]}^{\mathbf{2}\mathbf{+}}$

• ${\left[\mathrm{Ru}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Cl}\right]}^{2+}$ do not form geometrical isomers and optical isomers.
• $\left[{\mathrm{MA}}_5\mathrm{B}\right]$ type complexes do not show geometrical isomerism and optical isomerism.

(C) ${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Cl}\right]}^{\mathbf{2}\mathbf{+}}$

• ${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Cl}\right]}^{2+}$ do not form geometrical isomers and optical isomers.
• $\left[{\mathrm{MA}}_5\mathrm{B}\right]$ type complexes do not show geometrical isomerism and optical isomerism.

(D) ${\left[\mathrm{Ir}{\left({\mathrm{Pr}}_3\right)}_{2}H\left(\mathrm{CO}\right)\right]}^{\mathbf{2}\mathbf{+}}$

• ${\left[\mathrm{Ir}{\left({\mathrm{Pr}}_3\right)}_2\mathrm{H}\left(\mathrm{CO}\right)\right]}^{2+}$ form geometrical isomers, cis and trans.
• However, both the isomers contain a plane of symmetry, so optical isomerism is impossible.

Therefore, the correct option is (A) ${\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]}^{\mathbf{+}}$.