Electron transfer

9 Jun 2019

1FLO: PCET and Pourbaix

Submitted by Anne Bentley, Lewis & Clark College
Evaluation Methods: 

I graded each student’s problems as I would any other homework assignment, and they averaged about 80% on that part of the assignment. The other half of the total points for the assignment came from in-class participation.

Evaluation Results: 

We had a rich conversation about this article in class; it was probably one of the most interesting literature discussion conversations I’ve had. Although this was the only introduction to Pourbaix diagrams in the course, 12 of 15 students correctly interpreted a “standard” Pourbaix diagram on a course assessment.

 

Description: 

This set of questions is based on a single figure from Rountree et al. Inorg. Chem. 2019, 58, 6647. In this article (“Decoding Proton-Coupled Electron Transfer with Potential-pKa Diagrams”), Jillian Dempsey’s group from the University of North Carolina examined the mechanism by which a nickel-containing catalyst brings about the reduction of H+ to form H2 in non-aqueous solvent. Figure 3 in the article presents an excellent introduction to the use of Pourbaix diagrams and cyclic voltammetry to determine the mechanism of a proton-coupled electron transfer reaction central to the production of hydrogen by a nickel-containing catalyst.

Corequisites: 
Course Level: 
Learning Goals: 

Students should be able to:

-  identify atoms in a multidentate ligand that can coordinate to a metal as a Lewis base

-  outline the difference between hydride addition to a metal and protonation of a ligand in terms of changes to the overall charge of the complex

-  analyze a Pourbaix diagram to predict the redox potential and pKa of a species

Subdiscipline: 
Implementation Notes: 

I have discussed the challenge of integrating literature discussions into my inorganic course in a BITeS post and the VIPEr forums. Each spring I try something a little different. This year I used three articles from the literature to frame our review of course material at the end of the semester, with each literature discussion occupying a one-hour class meeting.

In each case, the students completed problems before coming to class. While these problems were based on the journal articles, they did not require the students to read / consult the journal articles in order to complete the assignment. The students brought an electronic or paper copy of the article to class. I usually put students in groups (approximately 3 per group) and gave each group new questions to work on, which did draw from the article. After some time working in groups, each group presented their material to the rest of the class.

In implementing this particular literature discussion, I didn’t have any further questions for them.  I walked through some of the other figures from the article (especially Figure 1).  We discussed the authors’ use of color in creating Figure 3. We also reviewed the significance of horizontal vs vertical vs diagonal lines. Because I had not covered Pourbaix diagrams in the course, the activity was a good introduction to the concept.

Because these problems don’t require consultation with the article, they are suitable to use on an exam.

Time Required: 
varies
8 Jun 2019

VIPEr Fellows 2019 Workshop Favorites

Submitted by Barbara Reisner, James Madison University

During our first fellows workshop, the first cohort of VIPEr fellows pulled together learning objects that they've used and liked or want to try the next time they teach their inorganic courses.

26 Mar 2019

Redox-switch polymerization catalysis

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

I am really unsure at this point. I may use the 1FLO version of this as a series of exam quesitons, or I may have the students work on this literature discussion in class. Either way, I am excited to see what they will do with it.

Description: 

This is the full literature discussion based on a communicaiton (J. Am. Chem. Soc. 2011133, 9278). This paper describes a redox-switch yttrium catalyst that is an active catalyst for the polymerization of L-lactide in the reduced form and inactive in the oxidized form. The catalyst contains a ferrocene-based ligand that serves as the redox active site in the catalyst. This full literature discussion is an extension of the one figure literature discussion that is listed below. In addition to presenting all of the same questions as that learning object, this includes interpretation of the XANES spectra presented in the paper. It also asks the students to identify the monomer and polymer in the reaction of interest. A possible extension of this learning object would be to have students examine and take measurements from the crystal structure presented in the paper in order to support the apparently low electron count on the yttrium catalyst. The Covalent Bond Classification system for counting electrons is used in this learning object.

Corequisites: 
Course Level: 
Learning Goals: 

A student should be able to apply their knowledge to 

  1. describe and interpret a plot of conversion vs. time
  2. count electrons and determine valence states in organometallic compounds
  3. determine if an organometallic compound is an oxidizing or reducing agent
  4. decipher a first-order kinetic plot
  5. interpret XANES spectra to determine the valence of iron in the catalyst
Subdiscipline: 
22 Mar 2019

1FLO: Redox-switch polymerization catalysis

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

I am really unsure at this point. I could certainly see this being used as a series of exam questions or have students take a few minutes to think about the questions individually and then have them share with a small group and present their thoughts in class. This is actively interpreting a figure from the literature with almost no context. As such, it is certainly going to be indicative of their understanding of other ideas and concepts.

Description: 

This is what I hope will be a new classification of learning object called a one figure learning object (1FLO). The purpose is to take a single figure from a paper and present students with a series of questions related to interpreting the figure. This literature discussion is based on a paper (J. Am. Chem. Soc. 2011, 133, 9278) from Paula Diaconescu's lab in which a yttrium polymerization catalyst with a ferrocene-based ligand can effectively be rendered active or inactive depeneding on the valence state of the ligand. The figure chosen from the paper shows the conversion of the monomer (L-lactide) to polymer over the course of time. During the reaction, the valence state of the ligand is changed and the rate of polymerization is significantly impacted. While the purpose of this LO was to limit consideration to a single figure, there is so much to mine from this communication that a companion literature discussion was developed to go into more of the details that were presented. Certainly this 1FLO can stand alone or be used in conjunction with the companion literature discussion. The Covalent Bond Classification system for counting electrons is used in this learning object.

Corequisites: 
Subdiscipline: 
Learning Goals: 

A student should be able to apply their knowledge to

  1. describe and interpret a plot of conversion vs. time
  2. count electrons and determine valence states in organometallic compounds
  3. determine if an organometallic compound is an oxidizing or reducing agent
  4. decipher a first-order kinetic plot
Course Level: 
Implementation Notes: 

I have yet to use this but I anticipate doing so in the fall. I hope it works as well as I think it can. It is such a simple plot and yet it is so rich in chemistry. I have a feeling I am going to have a very hard time containing myself to just this LO and not using the companion full Literature Discussion.

Time Required: 
Unknown but I think it could be as short as 15 minutes

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