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CHEM202: Advanced Inorganic Chemistry

Unit 4: Electronic Spectra of Transition Metal Complexes   As mentioned in the previous unit, electrons in d orbitals can be easily excited to higher energy d orbitals.  The intense colors of transition metal complexes are indicative of these transitions.  The unique absorption spectra that arise from metal complexes are often used in trace metal analysis by spectrophotometric techniques.  Electronic excitations are measured using UV-Vis spectroscopy, which will be discussed in this unit.  Other spectroscopic techniques used for metal complexes will be discussed in the next unit.  

Unit 4 Time Advisory
This unit should take you approximately 11.5 hours to complete.

☐    Subunit 4.1: 4.0 hours

☐    Subunit 4.2: 2.0 hours      

☐    Subunit 4.3: 2.5 hours

☐    Subunit 4.4: 1.0 hour

☐    Subunit 4.5: 2.0 hours
 

Unit4 Learning Outcomes
Upon successful completion of this unit, the student will be able to:

  • Discuss the colors of transition metal complexes with regard to electronic transitions.
  • Describe the interaction of UV-Visible light with inorganic complexes and how the spectra are produced.
  • Define the different parts of Tanabe-Sugano diagrams and how they are used to interpret spectra or predict photophysical properties.
  • Identify allowed and forbidden electronic transitions based on vibrational and rotational selection rules.
  • Explain the phenomena of metal-ligand charge transfer and ligand-metal charge transfer.

4.1 Introduction to the Electronic Transitions and Colors in Transition Metal Complexes   - Lecture: MIT: Principles of Chemical Science, Fall 2008: “Lecture 30: Magnetism and Spectrochemical Theory” Link: MIT: Principles of Chemical Science, Fall 2008: “Lecture 30: Magnetism and Spectrochemical Theory” (Adobe Flash, Mp4, or iTunes)
 
Also available in:
YouTube
 
Instructions: Please watch the lecture (runtime = 39:22 minutes).  This material demonstrates, theoretically and visually, the ability of metal complexes to appear as radically different colors based on the type of ligand and its interaction with the metal.
 
Terms of Use: Please respect the terms of use displayed on the webpage above. 

  • Reading: Jim Clark’s Chemguide: “The Colours of Complex Metal Ions” Link: Jim Clark’s Chemguide:  “The Colours of Complex Metal Ions” (HTML)
     
    Instructions: Please read the entire webpage.  This material discusses the physical process of color perception as well as the electronic properties that created colored complexes.
     
    Terms of Use: Please respect the terms of use displayed on the webpage above.

  • Reading: UC Davis: ChemWiki’s “Colors of Coordination Complexes” Link: UC Davis: ChemWiki’s “Colors of Coordination Complexes” (HTML)
     
    Instructions: Please read the entire webpage and work through the three examples within the text.  This material demonstrates how the crystal field and ligand field theories are applied to predict photophysical properties of transition metal complexes.  
     
    Terms of Use: Please respect the terms of use displayed on the webpage above.

4.2 UV-Vis Spectra   - Reading: University of Alberta’s Inorganic Chemistry Spectroscopy Tutorial: “UV-Visible Spectroscopy” Link: University of Alberta’s Inorganic Chemistry Spectroscopy Tutorial” “UV-Visible Spectroscopy” (HTML and Adobe Flash)
 
Instructions: Please navigate the pages of the tutorial on UV-Vis spectroscopy.  Be sure to click on the links within the presentation for answers to questions and supplemental information.  This material explains how UV-Vis light interacts with inorganic complexes to produce UV-Vis spectra.
 
Terms of Use: Please respect the terms of use displayed on the webpage above.

4.3 Tanabe-Sugano Diagrams   - Reading: UC Davis: ChemWiki’s “Tanabe-Sugano Diagrams” Link: UC Davis: ChemWiki’s “Tanabe-Sugano Diagrams” (HTML)
 
Instructions: Please read the entire webpage.  The material shows how Tanabe-Sugano diagrams are used to analyze spectroscopic data and manipulate photophysical properties of complexes.  Please also work through the five questions at the bottom of the webpage.  
 
Terms of Use: Please respect the terms of use displayed on the webpage above.

4.4 Charge Transfer in Electronic Spectroscopy   - Reading: UC Davis: ChemWiki’s “Electronic Spectroscopy: Interpretation” Link: UC Davis: ChemWiki’s “Electronic Spectroscopy: Interpretation” (HTML)
 
Instructions: Please read the entire webpage.  The material is a review of electronic spectra; however, it also discusses metal-ligand and ligand-metal charge transfer in metal complexes.
 
Terms of Use: Please respect the terms of use displayed on the webpage above.

4.5 Selection Rules of Electronic Transitions   - Reading: UC Davis: ChemWiki’s “Selection Rules and Transition Moment Integral” Link: UC Davis: ChemWiki’s “Selection Rules and Transition Moment Integral”
 
Instructions: Please read the entire webpage.  The material explains allowed and forbidden electronic transitions with reference back to character tables discussed in Unit 1.  It also provides vibrational and rotational selection rules.
 
Terms of Use: Please respect the terms of use displayed on the webpage above.

  • Reading: University of the West Indies: Robert J. Lancashire’s “Selection Rules for Electronic Spectroscopy” Link: University of the West Indies: Robert J. Lancashire’s “Selection Rules for Electronic Spectroscopy” (HTML)
     
    Instructions: Please read the entire webpage.  The material presented is a concise summary of the spin and LaPorte (orbital) selection rules of electronic spectra.
     
    Terms of Use: Please respect the terms of use displayed on the webpage above.