Shapes of Complex Ions (A2 Only)
Chemistry: AQA A Level, topic 4.2.3
Shape of Complex Ions
Complex ions display many different shapes depending on the metal and the ligands involved.
Geometries
- There are four main geometries for complex ions.
- Octahedral: commonly seen with small ligands like water and ammonia.
- Tetrahedral: commonly seen with large ligands like chloride.
- Square planar: commonly seen with the metals Ni, Pd, Pt.
- Linear: very rare and only seen for Cu, Ag, Au.
Square planar complexes
- Square planar complexes are usually only seen for the metals Ni, Pd, Pt.
- The reasons for this are complex.
- Square planar complexes can also have cis-trans (Z/E) isomerism.
- This is illustrated for the complex [Pt(NH3)2Cl2] above.
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Linear complexes
- Linear complexes are only seen for Cu, Ag, and Au.
- A good example of a linear complex is [Ag(NH3)2]+.
- This is the ingredient in Tollen's reagent.
Isomerism of Complex Ions
Complex ions display several kinds of isomerism.
Cis/trans isomers
- Cis/trans isomerism is a bit like E/Z isomerism.
- When two groups are on the same side, they are cis.
- When two groups are on opposite sides, they are trans.
Cis/trans isomers
- An example is the complex [Ni(H2O)4)Cl2].
- The chlorine and water groups can either be on the same or different sides, as shown.
- Cis/trans isomerism is also very common in square planar structures.
Optical isomerism
- Octahedral molecules with three bidentate ligands exist as pairs of enantiomers.
- This is illustrated for a nickel complex above. image: Ni(en)3 isomers.
Test yourself on Shapes of Complex Ions (A2 Only)
An octahedral complex containing three bidentate ligands can exist as pairs of what?
What type of isomerism does [Ni(H2O)4Cl2] show?