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3d-block Transition Metal Advanced A Level Inorganic Chemistry: Appendix 3 Complexes of the 3d block transition metals: more on formula, shapes and types of isomerism of complexes

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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.

Read Appendix 2. Introduction to complexes & ligands first

  • The principal shapes of transition metal complexes:

    • Examples of complexes have been described in Appendix 2

    • For isomerism analysis it is 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.

    • Based on the complex ion shape - usually determined by the ligands themselves (as opposed to lone pair involvement).

    • Octahedral (co–ordination number 6): very common, positional geometrical (E/Z isomerism) and optical (R/S) isomerism possible.

    • Tetrahedral (co–ordination number 4): with more bulky ligands like chloride ion, R/S optical isomerism possible but rare.

    • 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.

    • Three are illustrated in the diagram above, and the isomerism in three cases illustrated below.

  • Principal forms of isomerism:

    • E/Z isomerism (was called cis/trans geometric isomerism, but Z = cis and E = trans, so take care):

      • 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

      • cisplatin

        • 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

    • -

    • R/S isomerism (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.

        • For the complex [Cr(en)3]3+. The diagrams would be the same as above.

INORGANIC Part 10 3d block TRANSITION METALS sub–index:

10.1–10.2 Introduction to 3d–block Transition Metal chemistry

10.3 Chemistry of Scandium  *  10.4 Chemistry of Titanium

10.5 Chemistry of Vanadium  *  10.6 Chemistry of Chromium

10.7 Chemistry of Manganese  *  10.8 Chemistry of Iron

10.9 Chemistry of  Cobalt  *  10.10 Chemistry of Nickel

10.11 Chemistry of Copper  *  10.12 Chemistry of Zinc

10.13 Selected chemistry of other Transition Metals e.g. Ag and Pt

Appendix 1. Hydrated salts, acidity of hexa–aqua ions

Appendix 2. Complexes and ligands

Appendix 3. Complexes and isomerism

Appendix 4. Electron configuration and colour theory

Appendix 5. Redox equations, feasibility of reaction, Eø calculations

Appendix 6. Catalysis - types and effectiveness

Appendix 7. Redox equations - construction and balancing

Appendix 8. Stability constants of complexes and entropy changes

Appendix 9. Colorimetric analysis and determining a complex ion formula

Appendix 10 3d block – extended data table

Appendix 11 3d–block transition metal 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

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