My Notes
Categories
This inert atmosphere laboratory exercise will allow students to observe the difference in the electronic structure of coordination compounds of 12-crown-4 and cyclen with either Eu(II) or Eu(III). Since these ions have drastically different transitions students will observe a showcase that displays the difference in allowed vs forbidden transitions. Students will also be able to rationalize crystal field splitting differences using the spectrochemical series. DFT results using GAMESS are used to support conclusions from the spectroscopy.
| Attachment | Size |
|---|---|
| Lab Handout | 44.97 KB |
| Eu DFT calculated MOs.pdf | 912.61 KB |
A student will be able to identify key orbitals involved in the electronic transitions
A student will be able to explain the difference in color of Eu(II) compounds using the spectrochemical series and/or crystal field theory
A student will be able to explain the difference in intensity between allowed and forbidden transitions
A student should be able to identify high energy oscillators and apply that knowledge to explain observed luminescent intensity
Glovebox (O2 less than 5 ppm)
Fluorimeter
Spectrophotometer
Use volumetric glassware to make the solutions so that your concentrations will have a 1:2 stoichiometry between the Eu and the ligand. I also have a bottle with the degassed acetonitrile ready to go for them in the box.
The oxidation by allowing air exposure does take time. The student will also need to recap and invert the cuvette a few times to allow for the O2 to mix well.
Evaluation
Students are evaluated using their lab reports. The activity includes guiding questions for pre- and postlab portions.
Students that engage with the prelab questions and explain their answers are able to discern why the spectra change in energy and intensity with little coaching.
Typical confusion arises from the way crystal field splitting would interact with a f to d transition vs the heuristic from d to d transitions.
Students often consider acetonitile a "weaker" ligand, using lability rather than the spectrochemical series.
Students have also confounded internal conversion with vibrational quenching when explaining the weaker intensity of Eu3+ in cyclen vs 12-crown-4.