Chiral complex from the following is: (en = ethylene diamine)

🧠 Chiral = No Plane/Centre of Symmetry

A complex is chiral if it lacks all mirror planes and improper axes. Cis-bis-bidentate octahedrals are the textbook chiral case.

🗺️ Evaluate Each

| Complex | Symmetry features | Chiral? | |---|---|---| | cis-$[\mathrm{PtCl_2(en)_2}]^{2+}$ | Octahedral, 2 cis Cl + 2 en. Pure $C_2$ axis only — no mirror plane. | ✓ Chiral | | trans-$[\mathrm{PtCl_2(en)_2}]^{2+}$ | $C_{2h}$ symmetry — has horizontal mirror plane | ✗ | | cis-$[\mathrm{PtCl_2(NH_3)_2}]$ | Square planar (Pt(II)) → has $\sigma_v$ plane | ✗ | | trans-$[\mathrm{Co(NH_3)_4 Cl_2}]^+$ | Octahedral $D_{4h}$, has multiple mirror planes | ✗ |

🗺️ Geometry Check on Pt(II)

Wait — Pt(II) is d⁸ and usually square planar. But $[\mathrm{PtCl_2(en)_2}]^{2+}$ is Pt(IV) (charge balance: $x + 2(-1) + 2(0) = +2 \Rightarrow x = +4$). Pt(IV) is d⁶ → octahedral. So cis vs trans isomerism applies normally.

⚡ Octahedral Chirality Cheat Sheet

| Type | Chiral? | |---|---| | cis-$[M(AA)_2 X_2]$ | ✓ (Δ/Λ enantiomers) | | trans-$[M(AA)_2 X_2]$ | ✗ | | $[M(AA)_3]$ tris-bidentate | ✓ | | Any with $\sigma$ plane | ✗ |

⚠️ Square Planar Generally Not Chiral

Square planar complexes have a horizontal mirror plane through the metal — chirality is rare in square planar geometry (need very specialised ligand arrangements).

$\boxed{\text{Answer: (1) cis-}[\mathrm{PtCl_2(en)_2}]^{2+}}$