Question

Among the complex ions, ${{\left[ Co{{\left( N{{H}_{2}}.C{{H}_{2}}.C{{H}_{2}}.N{{H}_{2}} \right)}_{2}}C{{l}_{2}} \right]}^{+}}$, ${{\left[ CrC{{l}_{2}}{{\left( {{C}_{2}}{{O}_{4}} \right)}_{2}} \right]}^{3-}}$, ${{\left[ Fe{{\left( {{H}_{2}}O \right)}_{4}}{{\left( OH \right)}_{2}} \right]}^{+}}$, ${{\left[ Fe{{\left( N{{H}_{3}} \right)}_{2}}{{\left( CN \right)}_{4}} \right]}^{-}}$, ${{\left[ Co{{(N{{H}_{2}}-C{{H}_{2}}-N{{H}_{2}})}_{2}}(N{{H}_{3}})Cl \right]}^{2+}}$ and ${{\left[ Co{{(N{{H}_{3}})}_{4}}\left( {{H}_{2}}O \right)Cl \right]}^{2+}}$, the number of complex ion(s) that show cis-trans isomerism is:

Answer 1

Hint: Think about the stereoisomerism in coordination complexes. Look at the structures of all the complex ions given in the question and then classify whether the isomerism has cis-trans isomerism or not. Count the total number of isomers which exhibit cis-trans isomerism to get the answer.

Complete answer:
- Geometrical isomerism in coordination complexes is also known as cis-trans isomerism.
- In geometrical isomerism, the molecular formula remains the same but the point of contact of ligand with metal atom changes. If there are two same ligands present in the complex then, the complex is said to have geometrical isomerism.
- If the two same ligands are present adjacent to each other in a complex then, the isomer is said to be a cis-isomer.
- If the two same ligands are present at exactly opposite positions to each other in a complex then, the isomer is said to be a trans-isomer.
- ${{\left[ Co{{\left( N{{H}_{2}}.C{{H}_{2}}.C{{H}_{2}}.N{{H}_{2}} \right)}_{2}}C{{l}_{2}} \right]}^{+}}$, ${{\left[ CrC{{l}_{2}}{{\left( {{C}_{2}}{{O}_{4}} \right)}_{2}} \right]}^{3-}}$, ${{\left[ Fe{{\left( {{H}_{2}}O \right)}_{4}}{{\left( OH \right)}_{2}} \right]}^{+}}$, ${{\left[ Fe{{\left( N{{H}_{3}} \right)}_{2}}{{\left( CN \right)}_{4}} \right]}^{-}}$, ${{\left[ Co{{(N{{H}_{2}}-C{{H}_{2}}-N{{H}_{2}})}_{2}}(N{{H}_{3}})Cl \right]}^{2+}}$ and ${{\left[ Co{{(N{{H}_{3}})}_{4}}\left( {{H}_{2}}O \right)Cl \right]}^{2+}}$ are the given complex ions given in the question.
- Let’s check which complex ions have two same ligands.
- ${{\left[ Co{{\left( N{{H}_{2}}.C{{H}_{2}}.C{{H}_{2}}.N{{H}_{2}} \right)}_{2}}C{{l}_{2}} \right]}^{+}}$- This is dichloridobis-(ethylenediammine)cobalt(III) ion. It has two ethylenediammine (en) ligands and two chlorine ligands. Therefore, this complex has geometrical isomerism.
- ${{\left[ CrC{{l}_{2}}{{\left( {{C}_{2}}{{O}_{4}} \right)}_{2}} \right]}^{3-}}$- This is bis-(acetylacetonato)dichloridochromium(III) ion. It has two acetylacetone (acac) ligands and two chlorine ligands and therefore, it has geometrical isomerism.
- ${{\left[ Fe{{\left( {{H}_{2}}O \right)}_{4}}{{\left( OH \right)}_{2}} \right]}^{+}}$- This is tetraaquadihydroxidoiron(III) ion. It has two hydroxide ligands and so, it has geometrical isomerism.
- ${{\left[ Fe{{\left( N{{H}_{3}} \right)}_{2}}{{\left( CN \right)}_{4}} \right]}^{-}}$- This is diamminetetracyanidoferrate(III) ion. It has two ammonia ligands and so, it has geometrical isomerism.
- ${{\left[ Co{{(N{{H}_{2}}-C{{H}_{2}}-N{{H}_{2}})}_{2}}(N{{H}_{3}})Cl \right]}^{2+}}$- This is amminechloridobis-(methylenediammine)-cobalt(III) ion. It has two diaminomethane ligands and so, this complex has geometrical isomerism.
- ${{\left[ Co{{(N{{H}_{3}})}_{4}}\left( {{H}_{2}}O \right)Cl \right]}^{2+}}$- It is tetraammineaquachloridocobalt(III) ion. This complex doesn’t have only two ligands. It has four ammonia ligands. But due to the absence of two distinct same ligands, this complex will not show geometrical isomerism.
- Therefore, five complex ions out of six given complex ions show geometrical isomerism.
- Therefore, the number of complex ion(s) that show cis-trans isomerism is five.

Note:
Remember cis-trans isomerism is known as geometrical isomerism. The coordination complexes which exhibit geometrical isomerism will have at least a pair of same ligands present in the complex. Geometrical isomerism is a type of stereoisomerism.