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I have long taught CFAE as a topic in my inorganic class, but only over the last 3-5 years has the concept really solidified with me. I think this exercise really does a good job explaining that even a simple theory can have predictive power. I have not seen this analysis in a textbook. Lots of books discuss CFAE and its impact on rate, but taking it to the next step and benchmarking it on real data and ∆o values, I have not seen. Maybe it is because I am not a kineticist and don’t see the “obvious” implications of this. In any event, I wanted to track down some real data to benchmark the claims and I think that this worksheet does a nice job summarizing the theory, and why it works, and with real data to support it.
Note to instructors, I do not differentiate in my class between CF and LF concepts. I only discuss CF and then move on to MO theory.
| Attachment | Size |
|---|---|
| 2024 update to CFAE LO in word format | 31.01 KB |
| 2024 update to CFAE LO in pdf format | 237.48 KB |
students will calculate crystal field activation parameters from relative orbital energies
students will see the concept of crystal field activation energy
students will use his/her knowledge of CFAE to calculate relative rates for ligand substitution reactions
Students will understand the limitations of a simple theory
none
I have only done this as a lecture, specifically comparing Mn(III) and Cr(III) water exchange rates using ∆CFSE concepts. However, I finally tracked down some good representative data for both hs and ls complexes and I hope to use this worksheet in class or as a homework assignment in the future.
I hope to include a few slides about this topic to help illustrate some of the concepts of activation energy at a later date. To introduce it in lecture class, I draw a reaction coordinate free energy diagram with an octahedral complex as the starting complex and a square pyramidal complex as the transition state. I then estimate the activation energy as "one ligand bond strength" and the additional activation energy as the ∆CFSE.
An instructor may wish to have the students derive the ∆∆G‡ equation instead of just giving it to them, in which case, simple modifications to the document would allow this to be another evaluation of student understanding. I suppose it depends on how heavily you teach kinetics before this point. I do not teach a lot of kinetics so for my class, giving them the equations is definitely the right call... for now.
Evaluation
I would grade the calculated values as correct or incorrect. The more open ended responses would probalby not be graded but I might take the general sense of the class and lead a discussion on misconceptions or important points in the next class period.
TBD!
I found some small typos/sign errors in the key dated from 2020 so I have uploaded corrected keys and hidden the old keys. I also made a few additions (minor) to clarify the calculations.