shapes isomerism of transition metal complexes cis/trans E/Z isomerism chirality R/S optical isomerism enantiomers 3d-block GCE AS A2 IB A level inorganic chemistry revision notes

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Advanced inorganic chemistry: 3d block-transition metals - shapes & isomerism of complexes

Periodic Table - Transition Metal Chemistry - Doc Brown's Chemistry Revising Advanced Level Inorganic Chemistry Periodic Table Revision Notes

Appendix 3 Complexes: more on shapes and isomerism

The previous page described transition metal complexes in general, but here we focus on isomerism in transition metal complex ions. Examples of positional isomerism, R/S isomerism (optical isomers) and E/Z isomerism (trans/cis isomers) of transition metal complexes are described with the aid of diagrams.

GCSE/IGCSE Periodic Table Revision Notes

GCSE/IGCSE Transition Metals Revision Notes

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced level inorganic chemistry students US K12 grade 11 grade 12 inorganic chemistry - 3d block transition metal chemistry Sc Ti V Cr Mn Fe Co Ni Cu Zn

INORGANIC Part 10 3d block TRANSITION METALS sub–index: 10.1–10.2 Introduction 3d–block Transition Metals * 10.3 Scandium * 10.4 Titanium * 10.5 Vanadium * 10.6 Chromium * 10.7 Manganese * 10.8 Iron * 10.9 Cobalt * 10.10 Nickel * 10.11 Copper * 10.12 Zinc * 10.13 Other Transition Metals e.g. Ag and Pt * Appendix 1. Hydrated salts, acidity of hexa–aqua ions * Appendix 2. Complexes & ligands * Appendix 3. Complexes and isomerism * Appendix 4. Electron configuration & colour theory * Appendix 5. Redox equations, feasibility, E^ø * Appendix 6. Catalysis * Appendix 7. Redox equations * Appendix 8. Stability Constants and entropy changes * Appendix 9. Colorimetric analysis and complex ion formula * Appendix 10 3d block – extended data * Appendix 11 Some 3d–block compounds, complexes, oxidation states & electrode potentials * Appendix 12 Hydroxide complex precipitate 'pictures', formulae and equations

Advanced Level Inorganic Chemistry Periodic Table Index * Part 1 Periodic Table history * Part 2 Electron configurations, spectroscopy, hydrogen spectrum, ionisation energies * Part 3 Period 1 survey H to He * Part 4 Period 2 survey Li to Ne * Part 5 Period 3 survey Na to Ar * Part 6 Period 4 survey K to Kr and important trends down a group * Part 7 s–block Groups 1/2 Alkali Metals/Alkaline Earth Metals * Part 8 p–block Groups 3/13 to 0/18 * Part 9 Group 7/17 The Halogens * Part 10 3d block elements & Transition Metal Series * Part 11 Group & Series data & periodicity plots * All 11 Parts have their own sub–indexes near the top of the pages

Appendix 3. Complexes: more on shapes and isomerism

Valence shell electron pair repulsion theory (VSEPR) can quite often be used to predict the shape of a complex, which is usually one of four shapes (at least at pre–university level):
Principal shapes:
- Examples of complexes have been described in Appendix 2
- For isomerism analysis it crucial to the think of the orientation of the co-ordinate bonds and not the number of ligands.
- Isomerism can occur because of the directional nature of the dative covalent bonds emanating from the central metal ion.
- Octahedral (co–ordination number 6): very common, positional (E/Z) geometrical and optical (R/S) isomerism possible.
- Tetrahedral (co–ordination number 4): with more bulky ligands like chloride ion, optical isomerism possible.
- Square planar (co–ordination number 4): E/Z isomerism (geometrical/geometric cis/trans isomerism) possible.
- Linear (co–ordination number 2): relatively rare and can't form isomers
Principal forms of isomerism:
- E/Z isomerism (was called geometric isomerism):
  - Examples of (1) above with monodentate ligands in a square planar complex:
    - Z and E isomers (cis and trans) of [Pt(NH₃)₂Cl₂] shown below
    - You could not get isomers if it had a tetrahedral shape, you couldn't form two non-superimposable structures.
  - Examples of (2) above with unidentate ligands in an octahedral complex:
    - Z and E isomers (cis and trans) of [Cr(NH₃)₄Cl₂]⁺ or [Cr(H₂O)₄Cl₂]⁺ (shown below, same with NH₃)
    - and
- Optical isomerism: Examples of (3) above with a bidentate ligand.
  - and
  - (iv) the optical (R/S) isomers (mirror images) of [Co(H₂NCH₂CH₂NH₂)₃]²⁺ are represented above.
  - H₂NCH₂CH₂NH₂, ethane–1,2–diamine (ethylenediamine), is often represented in shorthand by en,
    - and the complex simply written as [Co(en)₃]²⁺.
    - This complex has mirror image forms i.e. enantiomers of optical isomers.
      - This optical isomerism can be illustrated thus
      - where L–L represents the electrically neutral ligand H₂NCH₂CH₂NH₂
      - The ligand bonds via the lone pairs of electrons on the nitrogen which are donated to form the metal–ligand dative covalent bonds.
      - The chromium(III) ion forms a similar complex exhibiting R/S isomerism.
        
        [Cr(en)₃]³⁺. The diagrams would be the same as above.

Doc Brown's Advanced Level Chemistry Revision Notes

Scandium * Titanium * Vanadium * Chromium * Manganese Iron * Cobalt * Nickel * Copper * Zinc * Silver & Platinum

Introduction 3d–block Transition Metals * Appendix 1. Hydrated salts, acidity of hexa–aqua ions * Appendix 2. Complexes & ligands * Appendix 3. Complexes and isomerism * Appendix 4. Electron configuration & colour theory * Appendix 5. Redox equations, feasibility, E^ø * Appendix 6. Catalysis * Appendix 7. Redox equations * Appendix 8. Stability Constants and entropy changes * Appendix 9. Colorimetric analysis and complex ion formula * Appendix 10 3d block – extended data * Appendix 11 Some 3d–block compounds, complexes, oxidation states & electrode potentials * Appendix 12 Hydroxide complex precipitate 'pictures', formulae and equations

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