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For years, I spent 2-3 days a semester working through Tanabe-Sugano diagrams, their development from terms, their evolution from Orgel diagrams, their analysis to give transition energies (the old ruler- trial and error analysis) and nephalauxetic parameters. Recently, colleagues in VIPEr convinced me that my time in class could be better spent, but I am not willing to completely give up on Tanabe-Sugano. For that reason, I have developed this exercise that boils the application of T-S diagrams down to an exercise in interpreting graphs (a skill which is sadly lacking in some of my students). It omits some of the analysis of the T-S diagram, but I think it gives adequate coverage to what is truly the most useful information to be gleaned from T-S diagrmams.
| Attachment | Size |
|---|---|
| Teaching Tanabe Sugano Diagrams.pdf | 44.91 KB |
A student should be able to identify the appropriate T-S diagram to use for a particular metal complex. A student should be able to predict whether a complex will be high-spin or low-spin and relate this to a particular position on the T-S diagram (x-axis). A student should understand that electronic transitions will not affect the value of either DelO or B, therefore any transition should be represented by a vertical line. A student should be able to predict the spin allowed transitions for a transition metal complex based on the appropriate T-S diagram. Given the necessary information to determine an exact x value (DelO/B), a student should be able to predict the energy of a particular electronic transition. A student should be able to convert n energy in wavenumbers to a wavelength in nm.
It may be helpful to provide students with rulers / straight edges. Students will need calculators.
It is helpful to have available for students a complete set of T-S diagrams, either from your textbook or photocopied.
Evaluation
As an in-class exercise, this activity is evaluated based on the quality of the discussion that is generated. Students work together in groups to apply their knowledge of electronic structure and graphs to answer the questions posed. It can be easily modified to serve as an exam -question for more direct assessment. For an exam, I may skip the first question, providing students with a single T-S diagram, and asking questions about a complex based on that T-S diagram.
Usually ,this particular example spurs some debate about whether the [Mn(H2O)6]3+ complex is in fact high-spin (because of the 3+ oxidation state. This in itself is a valuable review since it requires student reasoning of the effects on spin of metal identity, oxidation state and ligand field strength.
I used this again this semester with my Inorganic II (Transition Metal Inorg) class. First time I've used it since I posted the LO on VIPEr. We found a minor mistake in the key, in the allowed transitions once you change ligands to bpy. I'll fix the key as soon as I can, but the LO resulted in very nice discussion and the students responded favorably to the active learning involved.
Sheila,
I am using this exercise right now with my sophomore-level inorganic class. The students had a nice discussion about the high spin vs. low spin configurations of the [Mn(OH2)6]3+ cation. There was one small confusion, however, as we discussed the exercise - several students, as well as me, read the last question and thought that it implied that the [Mn(OH2)6]3+ cation was low-spin. This generated further discussion as class was ending. I asked them to think about how else we might independently determine the number of unpaired electrons... (We are currently using the Evans method in lab to determine the number of unparied electrons in Cr and Mn acac complexes.) I trying to find a literature reference for the magnetic moment of this complex for class on Wednesday.
Overall, I think this exercise is working quite well. Thanks!
Hi Sheila,
Thank you for posting! I recently used this activity as a refresher for students in a junior/senior level inorganic lab course. Students in this course have taken an inorganic lecture course in a previous semester and TS diagrams were briefly covered there. Once in our lab class they are expected to utilize TS diagrams in conjunction with lab data. The last time that this course was ran we noticed that students were struggling using TS diagrams. With that in mind I found your activity to be the perfect connect-the-dots scenario for them.
We had students work in groups of 3 for much of the time and then collectively discussed as a class and brought it to closure before the period was up. This activity sparked several great small groups discussions including the importance of geometry and ligand considerations as it relates to electronic transitions. I added one question which was to use the appropriate TS diagram to explain the weak absorptions seen in the [Mn(H2O)6]2+ spectrum. The class finished with a larger discussion about allowed transitions.
Overall this was a nice application of TS diagrams and gave our students the boost needed to now utilize these diagrams in their lab data analysis. I have talked with several students and their data analyses are on-track thus far.
All the best,
Rebecca
*Edit* I just found the key!