After I teach my students about magnetism and magnetic properties in coordination compounds, I spend a day showing how the data is collected and analyzed. I teach them about the Gouy balance, the Evans method of determining magnetism by NMR, and SQUID magnetometry. I also show them real data that I collected as an undergraduate or graduate student, and have them interpret and analyze it.
The only experiment that we can do locally is the Evans method, so I spend more time on this technique. We use the method during the metal acac laboratory.
This learning object includes a short powerpoint presentation outlining the basics of the method, some real data collected by students at Harvey Mudd College, and some links to primary literature in the field to help guide your teaching of the material.
A related learning object goes through the history of the field.
students will understand the basics governing the shift of the NMR signal in a magnetic environment
students, given a data set, will be able to determine the number of unpaired electrons in a coordination complex
none. If you want to collect your own data, then you will need an NMR spectrometer, a paramagnetic compound, and appropriate glassware.
I do this as a short lecture followed by problems done in small groups in class. If the students don’t finish the problems, they do them as homework.
The powerpoint has some notes to help with the presentation
There are 5 student datasets and a brief explanation
there is a faculty-only file which is an excel spreadsheet which does the calculations. The spreadsheet has the three-term, two-term and one-term versions of the equation, showing that the 2nd and 3rd terms can safely be ignored in most cases; the largest sources of error are the measurment of the mass and volume of the solution!
I usually ask a magnetism question on a homework and then again on my midterm or final exam. I give the students the equations they need. Importantly, for me, magnetic properties are used to help the students predict something about structure. For example, if a Ni(II) 4-coordinate 16-electron complex has unpaired electrons, that suggests that it is tetrahedral rather than square planar.
This is a fairly straightforward calculation, so the students generally do not have problems with the math (unless they forget to multiply the field strength of the NMR magnet by 1,000,000.