Thursday, May 1, 2014

A Mossbauer Spectroscopy problem

I believe this is the second post about Mossbauer Spectroscopy. The first one is here. So here is the problem that I saw in the book:

Some iron complexes in the form of FeX2(py)2 can be monomeric or polymeric as shown below (X=Cl, I).

Using the Mossbauer data given in the table below, determine which complex is polymeric.



First of all, for Iron we should know that the increased electron density at the nucleus will cause the isomer shift (IS) to decrease. Lower coordination number will also have a decreasing effect on IS. All these tell us that iodide complex will have the pseudo tetrahedral geometry like the one on left. 

I also know that complexes with lower symmetries have higher QS. This might explain the QS value for the iodide complex.

This problem was adapted from a publication:

If you read the paper, you will see that the authors did not have a crystal structure for the iodide complex. So, this problem is another example how useful Mossbauer Spectroscopy is. You can also read their discussion. To be correct, I read the paper first and then wrote my post.

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