Which one of the following types of isomerisms is shown by [CoCl₂(en)₂

Which one of the following types of isomerisms is shown by [CoCl₂(en)₂]Cl ?

[amp_mcq option1=”Optical isomerism only” option2=”Geometrical isomerism only” option3=”Both ionisation and geometrical isomerisms” option4=”Both geometrical and optical isomerisms” correct=”option4″]

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UPSC Geoscientist – 2024

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The complex ion is [CoCl₂(en)₂]⁺, which is an octahedral complex with coordination number 6. It exhibits both geometrical and optical isomerism.

The complex [CoCl₂(en)₂]⁺ is of the type [Ma₂b₂] (where ‘a’ is Cl and ‘b’ is the bidentate ligand ‘en’ represented by two coordination points). Such octahedral complexes can exist as cis and trans geometrical isomers. The trans isomer (where the two Cl ligands are opposite to each other) has a plane of symmetry and is optically inactive. The cis isomer (where the two Cl ligands are adjacent) lacks a plane of symmetry and is chiral, existing as a pair of enantiomers (non-superimposable mirror images), which are optically active.

Geometrical isomerism is shown by the existence of cis and trans forms. Optical isomerism is shown by the cis isomer due to its chirality. Ionisation isomerism involves the exchange of an ion inside the coordination sphere with a counter ion outside, which is not applicable here as the counter ion (Cl⁻) does not correspond to a ligand inside the sphere that can be exchanged. Linkage isomerism requires ambidentate ligands, which are not present here (en and Cl are not ambidentate).

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