JEE Chemistry 2023 Question with Solution

Given: Four coordination complexes are to be checked for chirality.

Find: Which complex is chiral.

Chirality in coordination complexes occurs when the complex lacks a plane of symmetry or centre of symmetry.

For the given complexes:

• cis–[PtCl$_2$(en)$_2$]$^{2+}$: The cis arrangement of ethylene diamine (en) ligands around the Pt centre creates a chiral structure.
• trans–[PtCl$_2$(en)$_2$]$^{2+}$: The trans arrangement is symmetric, so the complex is achiral.
• cis–[PtCl$_2$(NH$_3$)$_2$]: This complex has a plane of symmetry, so it is not chiral.
• trans–[Co(NH$_3$)$_4$Cl$_2$]$^+$: The trans arrangement makes the complex symmetric and achiral.

Therefore, the chiral complex is cis–[PtCl$_2$(en)$_2$]$^{2+}$. Hence, the correct option is A.

Given: The complexes differ by cis/trans arrangement and ligand type.

Find: The complex without symmetry elements responsible for achirality.

Use the rule:

• cis complexes with bidentate ligands such as en often become chiral.
• trans complexes are usually more symmetric and hence achiral.

Applying this:

1. In cis–[PtCl$_2$(en)$_2$]$^{2+}$, the two bidentate en ligands arranged in cis form produce non-superimposable mirror-image forms.
2. In trans–[PtCl$_2$(en)$_2$]$^{2+}$, the opposite placement introduces symmetry.
3. In cis–[PtCl$_2$(NH$_3$)$_2$], the ligands still allow a plane of symmetry.
4. In trans–[Co(NH$_3$)$_4$Cl$_2$]$^+$, the trans arrangement is symmetric.

So only cis–[PtCl$_2$(en)$_2$]$^{2+}$ is chiral.