Physical Chemistry: Quantum Mechanics
Evaluation was conducted by the instructor walking around the classroom and addressing individual problems students had.
From classroom observations, most students were able to properly count electrons and oxidation states for the metals in the complexes and rationalize the ligand coordination modes. Here, the main source of confusion was how to account for the Z-type Co-Zr interaction. The MO diagrams generated the most discussion and were the most difficult part for students (as was expected). The reactivity was also initially conceptually difficult for students, but once they realized how to treat the M-M bonded system, students were able to apply fundamental organometallic reactions to the system. Many students forgot what they had learned about magnetic moments in the previous quarter, but figured it out and were excited to apply knowledge from the previous course.
This problem set was designed to be an in-class activity for students to practice applying their knowledge of metal-metal bonding (as discussed in the previous lecture) to recently published complexes in the literature. In this activity, complexes from four papers by Christine M. Thomas and coworkers are examined to give students practice in electron counting (CBC method), drawing molecular orbitals, and fundamental organometallic reactions.
Following the activity, a student should be able to:
· Determine electron counts and oxidation states of complexes with M-M bonds using CBC electron counting method
· Draw molecular orbital diagrams for M-M bonds
· Determine M-M bond order
· Propose mechanisms for reactions at M-M centers
· Apply fundamental inorganic chemistry to reports in the literature
This was implemented in the second quarter of advanced inorganic chemistry (4th year level) before the second midterm as an in-class group activity. The worksheet generated a lot of interest from the students and generated good discussions in a class of 23 students. In the previous lecture, we discussed basic metal-metal bonding, including drawing MO diagrams and determining bond order for homobimetallic complexes. This worksheet was a reasonable extension, requiring students to apply this knowledge to more complicated systems.
see rubric that is attached
In the humanities it is common practice to read a piece of literature and discuss it. This is also practiced in science and is the purpose of this exercise. Each student is assigned a communication from the current literature (inorganic, JACS, organometallics, J. Phys. Chem) and the student presents this paper to the class. The class will also have the opportunity to read the article prior to the presentation, and I post each paper on my LMS page. The presenter will be responsible for explaining the paper, and leading a critical discussion. This is not an easy assignment since these papers are filled with chemical jargon, but an important part of their chemical education is to be able to tackle the literature. In addition a lot of this jargon is covered during the semester.
· Students will learn to read a paper from the primary literature
· Students will learn to present the a paper from the primary literature
· Students will learn to create a group discussion
· Students will learn how to relate chemical jargon learned throughout the four years of chemistry to the literature
· Students will learn how to answer exam questions from the primary literature
I hand out selected communications during the second week of class. Students are allowed to swap papers. They have the entire semester to read the paper and prepare a talk but the talks are during the last 3 weeks of class. Each student is give 25 min to present their paper to the class. The assignment is graded using the attached rubric and is worth 15% of their final grade. I selected about 7 exam questions for the final exam and ask students to answer 5 of these questions. I try to structure the questions so that they don't have to "know" every paper. I have attached an example of such a question.
The activity itself was not graded. However, the summary sheets (there are two; one in the middle; one one the last page) are turned in and graded as homework.
The exam questions are very similar to those of summary sheet 2. Last semester, 5 out of my 6 students successfully answered the similar final exam question. One still used the all-atom approach and didn't successfully determine the representation.
The SF6 summary sheet question is too hard for my C-level students. They tend to just give up before getting the representation correct. I will swap this for a smaller/less symmetric molecule in the next iteration. About 25% have trouble differentiating between the all atom gamma of the first summary sheet and the bond-only approach of the second and do the all-atom approach for the second summary sheet.
A guided inquiry activity where students use group theory and character tables to practice determining reducible representations for all atoms and the individual bonds (like CO stretches). The students then reduce the representation, determine which are vibrational modes, and then determine which are IR active using the character table. For the second portion, they practice using this approach to differentiate between two metal isomers.
- Identify reduced representations as translations, rotations, and vibrations
- Write reducible representations for both all-atom and particular vibrational motions
- Identify reduced representations as IR-active or inactive
- Use reduced representations and their IR activity to differentiate between molecular isomers
A character table. We have been using the online version at http://symmetry.jacobs-university.de/ if students forget their book. It displays nicely on their phones.
This is used in the senior-level advanced inorganic class. Students have practiced reducing representations in prior classes and should be comfortable with this step. I also assume that students have read the text section (we use Miessler and Tarr) on this topic. They have had a mini lecture on constructing gamma’s for molecular motions. Students work in small groups of 3-4 while I circulate among the groups. Generally, they check their work with another group at a nearby table. If time is an issue, you can formally assign individuals in a group to determine if the representation contains the A1/A2/B1T/etc representation. It is best to have the stronger students double check the weakest ones.
Students easily associate intensity of color with the concentration of a solute from their work in previous general chemistry and analytical chemistry courses. My goal in this exercise is to have them learn that the magnitude of the molar extinction coefficient is a measure of the intensity of the absorption and a function of the quantum mechanical allowedness of the transition. Physically observing the relative intensity of three solutions of the same concentration forces them to struggle with the concept of intensity of an absorption in contrast to the concept of the color that results from the energy of that absorption(s). In the faculty only files I have included an exam question I have given to evaluate student comprehension of this concept. This is a question I aspire for 100% perfect scores, however my data show that 3 students in a class of 15 (so around 20%) did not get a perfect score on this problem.
The following is a simple in-class “demonstration” that I use to segue between d to d and charge transfer transitions. After teaching about d to d transitions and Tanabe-Sugano Diagrams, I show my students three solutions that I have put in large test tubes before class. The three solutions I place in the test tubes are:
a. 10 ml of 0.1M Co(H2O)62+
b. 10 ml of 0.1M Cu(H2O)62+
c. 10 ml of a freshly prepared 0.1 M KMnO4 solution
We review what we have learned about using Tanabe Sugano diagrams to predict the maximum number of possible d to d transitions that could be observed for a given metal ion (with a given oxidation state, d electron configuration, and proposed high or low spin state) in the visible spectrum that give rise to color.
We then use observations of the KMnO4 solution to segue to the discussion of a different type of electronic transition: Charge Transfer.
I have also included an exam question that could be used to evaluate student understanding of the concept highlighted in the demonstration.
Demonstration to Segue Between d to d and CT Transitions
Learning Objectives: Going into this exercise:
1. Students should be able to determine the oxidation state and d electron count for a given set of metal complexes.
2. Students should be able to propose whether a metal complex should be high or low spin (or state whether high and/or low spin are irrelevant designations) for a given metal d electron configuration.
3. If they have learned about Tanabe-Sugano diagrams, students should be able to propose the maximum number of d à d transitions that could be observed for a given metal ion with a given d electron configuration and a given LS or HS designation.
3. Students should be able to visually compare three solutions of different metal complexes with the same concentration and recognize that they vary in color as well as intensity.
Following the Demonstration:
Students should be open minded and prepared to learn about why many transition metal complexes have the beautiful and intense colors that they do (over and beyond the color imparted by d to d transitions that fall in the visible).
This "Five slides about" is meant to introduce faculty and/or students to Spectroelectrochemistry (SEC), a technique that is used in inorganic chemistry research and other areas. SEC is a powerful tool to examine species that are normally hard to synthesize and isolate due to instability and high reactivity. Papers with examples of SEC techniques are provided on the last slide.
Students should be able to describe spectroelectrochemistry
Students should be able to conceptually explain how a spectroelectrochemical cell works
Students should be able to explain the benefits of spectroelectrochemistry as compared to standard synthesis and spectroscopy approches
Ideally, the students would take this introduction and then go and examine specific instances of SEC in the literature. Alternatively, this can be used to help explain research papers that are being discussed that use SEC techniques.
Students should already have an understanding of the basics of electrochemistry and spectroscopy prior to learning SEC, so this would be best suited for an upper division, special topics course in Inorganic Chemistry or Spectroscopy. There are some nice LO's on these techniques already on Ionic Viper (see related activities).
There are some good images of the specifics of SEC cell designs on company websites or journal articles (the Organometallics article shown in the web resources is one such article).
IR-SEC is included in the paper that is the focus of the "Dissection Catalysts for Artificial Photosynthesis" LO.
This five slides about chemical exchange transfer (CEST) discusses the magnetic properties of paramagnetic metal ions and their use as MR imaging agents. This includes tranditional contrast agents that affect the relaxation rate of nearby water protons and paramagnetic shift reagents suitable for CEST imaging applications. A recent redox-active cobalt complex is presented as an innovative agent for mapping redox imbalances in vivo.
Note: slides 2 and 3 are hidden. These slides present the basis of MR signal (slide 2) and relaxation mechanisms pertinent to T1 and T2 contrast agents (slide 3). This information is relevant to CEST agents since kex must be equal to or less than the frequency difference between the exhangeable protons and bulk water. Increasing the frequency difference between these two signals permits faster exchange, which may then outcompete T1 and T2 relaxation mechanisms.
Following presentation of these five slides, students will be able to:
- Discuss MR signal origin and why Gd(III)-based agents improve image contrast.
- Identify magnetic properties relevant to relaxation and shift agents.
- Rationalize the CEST phenomenon and why paramagnetic transition metals are suitable for developing CEST agents.
This LO was developed at the 2014 VIPEr Workshop: Bioinorganic Applications of Coordination Chemistry, and therefore has yet to be implemented in a classroom setting.
This Five Slides About was prepared specifically for the 2014 IONiC/VIPEr workshop Bioinorganic Applications of Coordination Chemistry held at Northwestern University July 13-18, 2014.
It covers, in one slide per technique, the techniques of electrochemistry (Cyclic Voltammetry), Electron Paramagnetic Resonance (EPR), Circular Dichroism (CD), X-ray Absorption Spectroscopy (XAS), NMR (specifically 2D-NMR for structural information), Chemical Exchange Saturation Transfer (CEST). This may seem an odd list, but it was chosen to prepare participants for the papers covered in the workshop.
It is intended to be paired with a collection of application assessment Questions, posted here on VIPEr, based on actual data from the literature. I encourage VIPEr users to add your own!
These slides contain animations, so they are not very useful for printing out.
Also, there is a LOT of information (references, teaching hints, etc ) in the NOTES section of the slides.
- A student should be able to explain the basics of each of the techniques included in this 5 Slides About: CV, EPR, CEST, NMR, CD, and XAS and to apply these teachniques to the interpretation of real data.
This LO is intended to be a quick introduction to the usefulness of these 6 techniques and their application to the characterization of bioinorganic samples.
Ideally, one would cover each slide (each technique) and then offer students the opportunity to apply their new knowledge to a piece of real data from the literature. I have posted several sets of Assessment Questions for that purpose.