9701 · 28.4
Stereoisomerism in transition element complexes flashcards
Revision flashcards for Cambridge 9701 Stereoisomerism in transition element complexes (syllabus 28.4). Flip, recall, then mark a real past-paper question.
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What are stereoisomers?
Compounds with the same structural formula (same atoms bonded to each other) but with a different arrangement of the atoms in space.
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What are the two types of stereoisomerism found in transition metal complexes?
1. Geometric (cis-trans) isomerism. 2. Optical isomerism.
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What is a cis-isomer in a square planar complex like `[Pt(NH₃)₂(Cl)₂]`?
The two identical ligands (e.g., Cl⁻) are on the same side of the central metal ion, at 90° to each other.
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What is a trans-isomer in an octahedral complex like `[Co(NH₃)₄Cl₂]⁺`?
The two identical ligands (e.g., Cl⁻) are on opposite sides of the central metal ion, at 180° to each other.
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Can a tetrahedral complex exhibit cis-trans isomerism? Why?
No. All ligand positions are equivalent and adjacent to each other (bond angles of 109.5°). There are no 'opposite' positions.
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What is an optical isomer, or enantiomer?
A molecule that is a non-superimposable mirror image of another. The molecule is described as chiral.
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What is the essential condition for a complex to be optically active?
It must be chiral, which means it must not possess a plane of symmetry.
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Why is a complex like `[Co(en)₃]³⁺` optically active?
The three bidentate ligands (en) arrange themselves like a three-bladed propeller. This arrangement is chiral, lacks a plane of symmetry, and its mirror image cannot be superimposed on the original.
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Can the complex `trans-[Co(en)₂(Cl)₂]⁺` exhibit optical isomerism?
No. The trans-isomer possesses a plane of symmetry that includes the cobalt ion and the two bidentate ligands, making it achiral.
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Can the complex `cis-[Co(en)₂(Cl)₂]⁺` exhibit optical isomerism?
Yes. The cis-isomer does not have a plane of symmetry. It is chiral and therefore exists as a pair of non-superimposable mirror images (enantiomers).
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What is cisplatin and why is its isomerism important?
Cisplatin is `cis-[Pt(NH₃)₂(Cl)₂]`. It is an effective anti-cancer drug. Its geometric isomer, transplatin, is biologically inactive, highlighting the importance of stereochemistry.