How many distinct stereoisomers (including optical isomers) are possible for the octahedral complex [M(phen)2Cl2] where phen is 1,10‑phenanthroline (bidentate) and Cl⁻ is monodentate, assuming the complex is neutral and the metal is in the +2 oxidation state?
Answer
3
The correct answer is 3 — Total stereoisomers = 1 (trans) + 2 (cis‑Λ, cis‑Δ) = 3.
Step-by-step solution
- Place two phen chelates (bidentate) in octahedral coordination sphere – they occupy four positions forming two chelate rings.
- Remaining two positions are taken by the two Cl⁻ ligands, which can be arranged either cis (adjacent) or trans (opposite).
- Trans arrangement is symmetric and not chiral – one isomer.
- Cis arrangement is asymmetric and gives a pair of enantiomers (Λ and Δ).
- Total stereoisomers = 1 (trans) + 2 (cis‑Λ, cis‑Δ) = 3.
Common mistake: Ignoring optical isomers of cis form
Concept tested: Stereochemistry of octahedral complexes
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