My Notes
Categories
This paper describes the synthesis and characterization of a Cr(I) dimer with a very short Cr-Cr distance. Computational studies support fivefold bonding between the chromium atoms. This paper could be used to introduce metal-metal multiple bonds and discuss the molecular orbital interactions of homonuclear diatomics including d-orbitals. More generally, it is a nice example to stimulate the discussion of what constitutes a bond and the various interpretations of bond order. This version of this learning object is a modified and expanded version of Maggie Geselbracht's original LO. It was prepared colleaboratively at the 2017 VIPEr Literature Discussion workshop.
| Attachment | Size |
|---|---|
| Questions for students | 50.5 KB |
Identify shapes and orientation of d orbitals
Create Lewis structures describing ligand binding type from crystal structures.
Apply symmetry concepts to assign orbital symmetries and create molecular orbital diagrams
Develop and draw the MO diagram of d-orbital interactions and use it to interpret the bonding involved in metal-metal multiple bonds.
Evaluate the relationship between bond order and experimental metal-metal bond distance
Evaluate effects of ligand design on molecular stability
Apply character tables for associated molecular point groups
Rationalize MO interactions of ligands with metal centers in the presence of a metal-metal multiple bond.
Students are asked to read the paper and answer the discussion questions before coming to class. This could be used in an inorganic course after you have talked about MO theory of diatomics but fairly early in our discussion of transition metal chemistry. There is a Perspectives article in Science that goes along with this paper that gives the MOs more explicitly.
Evaluation
Students are asked to answer the questions before coming to class and collected. After discussion students can revise their answers.
This is a newly revised learning object so no assessment has been collected yet.
Comments
I used this assignment as a literature discussion with my Inorganic Class (No P Chem pre-req). I used it to close out the MO chapter (5 in Meissler and Tarr). I really wanted to give the students a chance to apply what they worked to learn on a seemingly very complicated system that they had no experience with. Try to build their confidence that MO was a tool to apply to things as opposed to a batch of content to learn. I also wanted to replace lecture on delta bonding with a more active assignment.
I wrote a Pre-Class quiz and gave it through our LMS to make sure they read the paper. Then I used the questions posted above, with a few modifications, as a group exercise that I facilitated during a 75 minute lecture. I wrote a rubric to grade the quiz, their participation, and their responses.
I think it worked well to get the students to focus in on a relevant example. I don’t have any hard data to show it was more effective than what I did previously but I think it was easily more active than the lecture on this content i did previously. It did take too much time though, my goal was to complete it in one 75 minute class, so I assigned the remainder for homework.
I combined this literature discussion in my foundations level inorganic class with a second LO (https://www.ionicviper.org/class-activity/quadruple-bond-acrobatics). For the 2nd LO I asked for volunteers to complete the activity in the front of the classroom. Once they had formed I used this as a talking point about the metal-metal quintuple bond they had just read (present LO). I found this activity to really help in getting the discussion starting and somewhat broke the ice. The class had 36 students who were in 6 groups of 6 with one scribe per group. The scribe kept track of the conversation with everyone sitting in a circle they had all names on a piece of paper and drew lines from student to students as they discussed. I collected this and used it to help quantify in their grade how much they participated by counting the number of lines to their name. I walked around the room and to make sure 1) the conversation stayed on track and 2) to help when stuck.