1 Jul 2014

Hard Soft Acid Base Theory - Coordination Trends in Alkali Metal Crown Ether Uranyl Halide Complexes: The Series [A(Crown)]2[UO2X4] Where A = Li, Na, K, and X = Cl, Br

Literature Discussion

Submitted by Gerard Rowe, University of South Carolina Aiken

In this literature discussion, students are asked to read an article describing a series of uranyl halide compounds that contain an alkali counterion that interacts with one or more of the uranium's ligand atoms.  This paper stands out as a great example of the binding preferences of acids and bases, and can be explained very well using simple HSAB concepts.  Also notable in this paper is the fact that the authors claim that HSAB concepts explain their results very well in the introduction, and then only bring it up again almost as an afterthought in the short discussion section at the end of the paper.

Learning Goals: 

A student should be able to rank Lewis acid and bases in terms of relative hardness

A student should be able to interpret X-ray crystallographic structural data and identify structural motifs

A student should be able to explain the affinity that atoms have for one another in terms of HSAB theory


Implementation Notes: 

This activity is fairly straightforward, and my students needed little help working through the discussion questions.  For most students, this was the first time they had seen molecules represented as thermal ellipsoids, so they had a little trouble identifying the atoms inside molecules, but everyone got it by the end of the class.

Time Required: 
One 50 minute class period
Evaluation Methods: 

Students were evaluated on how completely they answered the pre-class reading questions.  

In-class discussion questions were collected at the end of the class period.  For these, students worked in groups of 2 or 3.

Evaluation Results: 

Most of the students grasped the major concepts by the end of the class, though there was a lot of initial confusion as to how to make sense of all the structural data in the paper.

The biggest hurdle students had to overcome was shifting their thinking from absolute terms (e.g., sodium is hard) to relative terms (e.g., sodium is harder than potassium).  Once they did this, the rest of the activity becomes very simple.

Creative Commons License: 
Creative Commons Licence


Thanks for this LO, Gerard. We read the article in my small advanced inorganic course this week, and I adapted many of your questions for my students to complete before class.

We were all curious to learn more about uranium chemistry and what kinds of precautions need to be taken in the lab. (We noticed that the reactions seemed to be on a fairly small scale.) If anyone has experience and could chimine in with stories, we'd love to hear them.

As a group, we were a bit flummoxed by the lack of attention given to compound 1. Its synthesis and characterization weren't described in the experimental section. Later the authors say that it's isomorphic with compound 2 and some X-ray data is included in the discussion, but it generally seemed hard to find information about it. 

These comments aren't meant to be a criticism of the LO - we're simply curious to learn more.  I think the students found the article fairly accessible, and everyone likes crown ethers!

Thank you for this LO! I adapted it for a take home exam, and I think that my students were really able to solidfy the HSAB concepts in a real world problem. The majority of them were able to explain the HSAB of the complexes and how they related to what we had learned in class.


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