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My institution has a powder diffractometer in the geology department so I have always tried to do a lab in my sophomore course that uses the instrument. I am much more familiar with single crystal, so I have gone delving for labs and am not really satisfied with any I have found. Ideally I would like students to make the compound, do some X-ray, learn something useful and fix the economy. Anyone have any suggestions?
Alas, I don't have a suggestion for you. My knowledge of powder diffraction, while once larger, now would not fill the head of a goniometer pin...
But I did think of a way to boost the economy. Somebody give me a good enough reason for buying a powder instrument, and I'll get one for HMC to teach the lab.
Adam
As a user of powder diffraction, I love this question! The problem is where to start! I don't think I can meet all of your criteria (particularly fix the economy), but I can help you put together something simple and (hopefully) effective.
At the very basic level, where you're only going to see the technique once (or maybe twice), there are two starting off points:
In which direction do you want to go?
In reply to so many possibilities... by Barbara Reisner / James Madison University
In reply to and one more...solid solutions by Maggie Geselbracht / Reed College
Thanks for getting involved here. I guess I should provide some background info. My class is sophomore level (although I usually have freshmen to seniors in the class). The lab is only required for BS chemistry majors, but I get others. The class is a common elective for chemical engineers, ie people who don't want to be in the class but have to be. Usually they don't take the lab, but some do. This is the only inorganic lab course students take unless they do research with me. And finally, the X-ray instrument can be a little fussy. There, that covers my situation.
I like the idea Maggie suggests, although the organometallic chemist in me shutters as I think about shake and bake chemistry from my grad school days. I worry about being able to run multiple samples on our instrument. I guess my overall goal is for the students to gain an appreciation for what we can learn using powder diffraction. With the students being freshmen and sophomores mostly, I don't want to get too advanced. This is really the only place they see X-ray in our curriculum, so it has to serve as an introduction. I would certainly love to see what Maggie is willing to share, and Barb, hopefully I have answered (1) on your list and we can keep on posting. (Sorry about my delay, my office computer died yesterday)
In reply to Answers with more questions by Chip Nataro / Lafayette College
Maggie beat me to the punchline on the type of experiments that I was most likely to suggest. If you don't care so much about learning to analyze data, using XRD as a fingerprinting tool is great. It's always fun to take a bunch of white powders and match them to a series of known possibilities. While I've never done it, I've always wanted to set my student to synthesize some paint pigments in the same color family so they could see why a technqiue like powder xrd can be used to identify forgeries because of the changes in compounds used to get a particular color.
If you want to do real data analysis, Maggie's suggestion on soid solutions is the way to go. Another system (whose synthesis is written up in JCE, I think) are the tungsten bronzes, NaxWO3. These can be grown from a melt by running a current through the solution. The colors are absolutely beautify and you will see diffferences in the xrd data. I'll have to take a look on the JCE search engine later.
One possibility that might appeal better to a molecular chemist would be (1) to do some isomorphous substitution (if there is enough difference in size of the metal ion, you should see a noticable change in the lattice parameters); (2) to look at coordination chemistry isomers (e.g. different inner and outer shell) which will have very different unit cells and hence powder patterns; or (3) to look at molecules that have several polymorphs. There are plenty of organic examples of case 3; I wish I had organic suggestion on the latter. What I think is so neat about these is that the polymorph produced during crystallization can have a profound effect on the activity of a drug.
In reply to similar ideas by Barbara Reisner / James Madison University
In reply to Ideas by Chip Nataro / Lafayette College
The JCE reference for the tungsten bronze lab is:
Conroy, L. E. "The preparation and characterization of a sodium tungsten bronze." J. Chem. Educ. 1977, 54, 45-49.
It's not a new paper, but I'd label it a as classic. PXRD is discussed as a characterization technique in the paper.
If you'd like to update the chemistry a bit and talk about new applications by related materials, you can check out a paper from Shiv Halasyamani's group at University of Houston (Inorg. Chem. 2008, 47, 8511-8517). While the synthesis in this paper doesn't meet your criterion, it would be a way to introduce neat properties of solid state materials.
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