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CHEM202: Advanced Inorganic Chemistry

Unit 8: Reaction Mechanisms of d-Metal Complexes   Ligands in a metal ion complex can be substituted by other ligands to give the new metal complex certain novel chemical or physical properties.  Ligand substitutions can occur via a number of different mechanisms.  In metal complexes with different ligands, some ligands can be substituted faster and easier than other ligands.  The geometries of molecules also play an important role in substitution reactions.  In order to make a prediction of the reaction product, the mechanism of ligand substitution must be identified.   

Unit 8 Time Advisory
This unit should take you approximately 7.5 hours to complete.

☐    Subunit 8.1: 2.5 hours

☐    Subunit 8.2: 4.0 hours

☐    Subunit 8.3: 1.0 hour        

Unit8 Learning Outcomes
Upon successful completion of this unit, the student will be able to:

  • Distinguish between kinetic and thermodynamic stability; define the chelate effect in relation to complex stability.
  • Describe reaction mechanisms of inorganic complexes.
  • Compare and contrast substitution reactions in square-planar and octahedral complexes, including the trans effect (trans influence).
  • Explain the mechanisms and reaction kinetics of photochemical and thermally-driven reactions. 

8.1 Equilibrium Constants and Stability of Coordination Compounds   - Reading: University of the West Indies: Robert J. Lancashire’s “Stability” Link: University of the West Indies: Robert J. Lancashire’s “Stability” (HTML)
 
Instructions: Please read the entire webpage.  The material makes an important distinction between kinetic and thermodynamic stability.
 
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  • Reading: University of the West Indies: Robert J. Lancashire’s “Stability, Chelation and the Chelating Effect” Link: University of the West Indies: Robert J. Lancashire’s “Stability, Chelation and the Chelating Effect” (HTML)
     
    Instructions: Please read the entire webpage and watch the seven-second video clip at the end of the text.  Please also attempt “CALCULATION # ONE” and “CALCULATION # TWO” contained within the text.  The chelate effect is presented with regard to stability and chelation.  It is important to note that monodentate ligands are easier to displace, and therefore they are considered less favorable, than polydentate ligands.
     
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8.2 Mechanisms of Ligand Substitution   - Reading: Jim Clark’s Chemguide: “Complex Metal Ions—Ligand Exchange Reactions” Link: Jim Clark’s Chemguide: “Complex Metal Ions—Ligand Exchange Reactions” (HTML)
 
Instructions: Please read the entire webpage.  The reactions presented here primarily deal with water displacement from hexaaqua complexes.  
 
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8.2.1 Kinetic and Thermodynamic Considerations   - Reading: University of Oxford: Dr. Dermot O’Hare’s “Introduction to Inorganic Reaction Mechanisms” Link:  University of Oxford: Dr. Dermot O’Hare’s “Introduction to Inorganic Reaction Mechnisms” (HTML)
 
Instructions: Please read the information covered on the webpage.  This material discusses general considerations and terminology of reaction mechanisms.  It is important to note that proposed mechanisms can never be proven, but some may be disproven.
 
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8.2.2 Substitution of Square Planar Complexes   - Reading: University of Oxford: Dr. Dermot O'Hare’s “Lecture 1” Link:  University of Oxford: Dr. Dermot O'Hare’s “Lecture 1” (HTML)
 
Instructions: Use the “next page” link in the upper right corner to navigate through the slides.  The presentation focuses on reaction mechanisms of square planar metal complexes.
 
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8.2.3 Substitution in Octahedral Complexes   - Reading: University of Oxford: Dr. Dermot O’Hare’s “Lecture 2” Link:  University of Oxford: Dr. Dermot O’Hare’s “Lecture 2” (HTML)
 
Instructions: Use the “next page” link in the upper right corner to navigate through the slides. The presentation focuses on reaction mechanisms of octahedral metal complexes.
 
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8.3 Reaction Kinetics   - Lecture: MIT: Principles of Chemical Science, Fall 2005: “Lecture 33: Ligand Substitution Reactions: Kinetics” Link: MIT: Principles of Chemical Science, Fall 2005: “Lecture 33: Ligand Substitution Reactions: Kinetics” (Adobe Flash, Mp4, or iTunes)
 
Also available in:
YouTube
 
Instructions: Watch the lecture (runtime = 46:18 minutes) on the kinetics of ligand substitution reactions.  Please also watch the beginning of Lecture 34 for the conclusion of the lecture on kinetics (approx 8:22 minutes).  It is important to note that reactions may be photochemically or thermally driven, and the same reactants could have completely different products depending on the mechanism. 
 
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