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This laboratory experiment is a quick and straightforward synthesis of a MoO2(acac)2 complex. The ligand set allows for two possible geometric arrangements: cis and trans. Using IR spectroscopy along with group theory analysis of the Mo-O stretching modes, students can determine which isomer they formed in their synthesis. NMR spectroscopy is also employed, and confirms the geometric arrangement due to the inequivalence of the acac methyl groups. The experiment provides a nice application of group theory principles learned in lecture, and also is a good way to (re)introduce common spectroscopic characterization tools.
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| LAB_MoO2(acac)2Synthesis_2025_Intro&Procedure_0.docx | 42.48 KB |
Upon completion of this laboratory experiment, students will be able to:
- Synthesize the coordination complex MoO2(acac)2
- Characterize their MoO2(acac)2 product using melting/decomposition point, IR spectroscopy, and NMR spectroscopy
- Use their experimental data to demonstrate they made the desired complex and discuss the purity of their product
- Determine whether their complex is in the cis- or trans-configuration after completing a group theory analysis for each isomer to predict the number of expected Mo-O stretching bands in the IR spectrum and comparing with their experimental data
- Explain how their NMR data supports their geometric assignment
- Standard synthetic equipment
- Melting point apparatus
- IR spectrometer
- NMR spectrometer
The authors of this LO each use this laboratory experiment in their inorganic chemistry course, but do so in slightly different ways. Extensive instructor's notes, including information on how each of us implements the lab in our own curriculum is provided in the included documents.
In general, this experiment is a relatively easy synthesis that is good for the beginning of a semester, or aligned specifically with a lecture unit on group theory. The synthesis and analysis can be performed in 1-2 laboratory periods of 3-4 hours, depending on the amount of in-class time you want to allocate for the students to analyze their spectroscopic data and complete the group theory analysis.
Also included in the provided documents are animations of the relevant vibrational modes for each configuration that can be shown to students to help them make connections between the motions and the symmetry assignments.
Evaluation
Example pre- and post-lab questions are provided. Students are evaluated on their laboratory notebook pages and their laboratory reports, including answer to questions and any writing requirements (such as an introduction, experimental, or results and discussion section).
Students typically get good yields from their syntheses and are able to complete the spectroscopic data collection and analysis with assistance from the TA or instructor. If students complete the group theory and spectroscopic analysis during class time, all typically arrive at the correct answers.
This is an excellent experiment. I worked with a senior undergraduate student to make the complex and characterize the formed complex.
Here are comments from the student:
The NMR spectra were clean. We measured NMR in CDCl3.