28.4 A2 Level

Stereoisomerism in transition element complexes

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Definition Flip

What type of isomerism is shown by [Pt(NH₃)₂Cl₂]?

Answer Flip

[Pt(NH₃)₂Cl₂] exhibits geometrical (cis/trans) isomerism due to its square planar geometry. The cis isomer has both NH₃ ligands (or both Cl ligands) adjacent to each other, while the trans isomer has them opposite each other.

Key Concept Flip

Draw and label the cis and trans isomers of [Co(NH₃)₄(H₂O)₂]²⁺.

Answer Flip

In the cis isomer, the two H₂O ligands are adjacent to each other. In the trans isomer, the two H₂O ligands are opposite each other.

Key Concept Flip

Explain why [Ni(H₂NCH₂CH₂NH₂)₃]²⁺ exhibits optical isomerism.

Answer Flip

[Ni(H₂NCH₂CH₂NH₂)₃]²⁺ exhibits optical isomerism because the complex is chiral. The three bidentate ligands coordinate to the central Ni²⁺ ion in a way that the molecule is non-superimposable on its mirror image.

Key Concept Flip

Describe the difference in polarity between cis and trans isomers of [Pt(NH₃)₂Cl₂].

Answer Flip

The cis isomer of [Pt(NH₃)₂Cl₂] is polar because the bond dipoles do not cancel out due to the adjacent arrangement of ligands. The trans isomer is non-polar because the bond dipoles cancel out due to the opposing arrangement of ligands.

Definition Flip

What are the requirements for a complex to exhibit geometrical isomerism?

Answer Flip

For geometrical isomerism (cis/trans), the complex must have two or more different ligands attached to the central metal ion and the ligands must be arranged in such a way that different spatial arrangements are possible. Typically seen in square planar and octahedral complexes.

Key Concept Flip

Explain why some octahedral complexes containing only monodentate ligands can display geometric isomerism.

Answer Flip

Octahedral complexes with monodentate ligands can display cis/trans isomerism if there are at least two of each type of ligand present. This allows for different spatial arrangements around the central metal ion.

Key Concept Flip

Is [Ni(H₂NCH₂CH₂NH₂)₂(H₂O)₂]²⁺ chiral? Explain.

Answer Flip

Yes, [Ni(H₂NCH₂CH₂NH₂)₂(H₂O)₂]²⁺ is chiral and can exist as optical isomers. The two bidentate ligands and two water ligands create a non-superimposable mirror image.

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28.3 Colour of complexes 28.5 Stability constants, Kstab