16 Jul 2008

Computational Modeling of a Molybdenum Piano Stool Complex

Lab Experiment

Submitted by Nathanael Fackler, Nebraska Wesleyan University
Course Level: 

This is a computational/molecular modeling supplement to the synthesis of  [1,3,5-C6H3(CH3)3]MoCO3 included in the third edition of  "Synthesis and Technique in Inorganic Chemistry" (see full citation below)*. Students optimize the model and compute an infrared spectrum and compare it to their experimental (solution) spectrum.

*G. S. Giorlami, T. B. Rauchfuss, R. J. Angelici  “Synthesis and Technique in Inorganic Chemistry: A Laboratory Manual”, Third Edition

PDF icon Experiment 16.pdf66.5 KB
Equipment needs: 

Computational software package such as the Gaussian.

Implementation Notes: 

Software training was minimal--an hour was devoted to using the GUI interface to Gaussian 03--and was accomplished during the first lab session. The majority of questions,which were generally software specific questions,were fielded as students did their modeling. Since this is computer based work, ready access to modeling software during laboratory sessions is required. My students do their experiments in a round-robin format, thus the number of computers needed during any single lab session is minimal (1-3), though for the initial training I did make use of a computer lab.Input of the model takes at most an hour,less if the students are reasonably familiar with the computational software,so students should be able to perform other work during a typical 3 hour lab session.

Time Required: 
1 hour
Evaluation Methods: 

Lab report.

Evaluation Results: 

Our attempts to utilize the free WebMO interface required that we import an optimized structure from Gaussian 03.The WebMO clean-up routine often wreaks havoc on models containing metals,so direct input into the WebMO interface becomes a significant chore. Results are generally quite respectable, which surprised a number of my students.The CO-Mo-CO angle is very close to the experimentally determined value and the calculated spectrum is comparable to the solution spectrum, suggesting accounting for solvent effects are not important in this computation.Of course the quality of the results of course depends on the computational method employed.Attempts to use semi-empirical methods all failed,as expected,nor are the calculations expected to be all that accurate.Refer to the latest literature and the web resource link provided for more general detail regarding the accuracy of various levels of calculations.The latter link is provided through NIST.

Creative Commons License: 
Creative Commons Licence


Have you had a chance to try this again on WebMO? It should work better with newer versions.

You can easily draw and "symmetrize" the molecule in WebMO now (2013), so this should work fine.

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