Stereoisomerism in complexes
Introduced| English | Meaning |
|---|---|
| stereoisomerism/ˈsterɪəʊɪsəmərɪzəm/ | The existence of compounds with the same atom connectivity but different arrangements in space. |
| square planar/skweə ˈpleɪnə/ | A flat shape with four bonds at 90°, found in some d-block complexes such as [PtCl4]2-. |
| octahedral/ˌɒktəˈhiːdrəl/ | Describing six positions arranged towards the vertices of an octahedron around a central point. |
| optical isomerism/ˈɒptɪkl ˈaɪsəmərɪzəm/ | Isomerism involving non-superimposable mirror-image molecules that can interact differently with plane-polarised light. |
| bidentate/baɪˈdenteɪt/ | Describing a ligand that forms two coordinate bonds to the same central metal ion. |
Isomers around a metal
- Complexes can show stereoisomerism 立体异构 — same bonds, different 3-D arrangement.
- Two kinds: geometrical and optical.
- It can even change the complex's polarity.
Complex stereoisomer lab
Classify complex isomers by ligand arrangement.
Transition-metal complexes can show both geometrical and optical isomerism.
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Square planar/octahedral complexes show cis/trans; octahedral ones with bidentate ligands show optical isomerism.
Octahedral complexes with two different ligand types can show cis-trans isomerism.
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A form of stereoisomerism in complexes.
Geometrical (cis/trans)
- Appears in square planar 平面正方形 complexes (e.g. $[\text{Pt}(\text{NH}_3)_2\text{Cl}_2]$) and octahedral 八面体形 ones.
- The two identical ligands are adjacent (cis) or opposite (trans).
Cis and trans isomers of a square planar complex
Geometrical (cis/trans) isomerism in [Pt(NH₃)₂Cl₂] means the two identical ligands are:
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In a square planar complex the matching ligands sit next to each other (cis) or across (trans).
Match each isomerism idea in complexes.
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Each item links the term to its correct meaning.
Optical isomerism 旋光异构
- Appears in octahedral complexes with bidentate 双齿 ligands, e.g. $[\text{Ni}(\text{en})_3]^{2+}$.
- It has two non-superimposable mirror images.
- Polarity: a cis form may be polar, while the trans form is often non-polar (its dipoles cancel).
Optical isomerism appears in octahedral complexes that have:
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Octahedral complexes with bidentate ligands can exist as two non-superimposable mirror images.
Compared with a cis complex, the matching trans complex is often:
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In the trans form the opposite ligands' dipoles cancel, so it is often non-polar.
Where isomerism appears
- Cis-trans isomerism occurs in octahedral and square-planar complexes with two ligand types.
- Some octahedral complexes also show optical isomerism.
You've got it
- geometrical (cis/trans): in square planar ([Pt(NH₃)₂Cl₂]) and octahedral complexes — ligands adjacent (cis) or opposite (trans)
- optical: in octahedral complexes with bidentate ligands (e.g. [Ni(en)₃]²⁺) — mirror images
- a cis complex may be polar; the trans form is often non-polar