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Chapter 7: Coordination Chemistry- Reactions and Mechanisms

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    Learning Objectives
    • Determine whether an metal ion will be labile or inert.
    • Use kinetic data to determine if a ligand substitution occurs by an associative or dissociative mechanism
    • Predict the product of a square planar ligand substitution reaction based on the trans effect and trans influence
    • Explain the difference between and inner sphere and outer sphere electron transfer reaction

    Thumbnail image shows the structure of the Creutz-Taube complex used to study inner sphere electron transfer reactions (CC0, Jynto via Wikimedia Commons)

    • Section 7.1: Thermodynamic Stability of Metal Complexes
      Experimentally, it is observed that metal complexes of polydentate ligands are significantly more stable than the corresponding complexes of chemically similar monodentate ligands; this increase in stability is called the chelate effect. For example, the complex of Ni(II) with three ethylenediamine ligands should be chemically similar to the Ni(II) complex with six ammonia ligands. In fact, the equilibrium constant for the formation of the ethylenediamine complex is almost 10 orders of magnitude
    • Section 7.2: Trends in Kinetic Lability
      Ligand substitution reactions span a wide range of timescales, from hundreds of years to fractions of a second. This section will explore why some metal ions have inherently fast ligand exchange rates while other have inherently slow rates.
    • Section 7.3: Ligand Substitution Mechanisms
      Ligand substitution is one of the simplest reactions a metal complex may undergo. In general, ligand substitution involves the exchange of one ligand for another, with no change in oxidation state at the metal center. The incoming and outgoing ligands may be neutral or ionic but the charge of the complex changes if the ligand charge changes. Keep charge conservation in mind when writing out ligand substitutions.
    • Section 7.4: The Trans Effect Observation
    • Section 7.5: The Trans Effect Explanation
      The trans effect is an ancient but venerable observation. First noted by Chernyaev in 1926, the trans effect and its conceptual siblings (the trans influence, cis influence, and cis effect) are easy enough to comprehend. That is, it’s simple enough to know what they are. To understand why they are, on the other hand, is much more difficult.
    • Section 7.6: Electron Transfer Reactions
      Henry Taube won the Nobel Prize (1983) for the study of electron transfer reactions in transition metal complexes, classifying such reactions into two mechanisms. The mechanism of electron transfer in which a bridging ligand is shared between two metals is called the inner-sphere mechanism, and the one involving a direct transfer of electrons between two metals without a bridging ligand is called the outer-sphere mechanism.

    Chapter 7: Coordination Chemistry- Reactions and Mechanisms is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.