I have prepared Zn (II) metal complexes with a neutral ligand derived from pyrazine. However, I use zinc sulfate for synthesis and I have not been able to know if the sulfate group is free or coordinated in my compound.
The FTIR spectrum of the compound shows a broad band at 1200 cm-1 of the sulfate group, but is superimposed by vibrations of the ligand.
Mr. Mescco,
The coordination to the metal ion as bridging ligand causes for decreasing in the symmetry and increasing in the number of the modes in the spectrum, comparing with the free SO42- showing higher symmetry and lower number of frequencies.
My strong recommendation is that you should do a family of the samples. So you should prepare Zn(II), and other metals with similar cation behaviour (e.g. Fe, Ca, Mg, etc) then measure the Raman/IR spectra of each of them. From these results, you will see a Raman-shift going up or down that depends on the Cation. Since you have the position for the different cations, you can build your own calibration curve that are specific for your prepared sulphate and methods.
Here are some examples:
Article The Raman study of certain sulfates
Article The stability of sulfate and hydrated sulfate minerals near ...
If you need more help, le me know.
Thank you very much to all. I found the answer in the book of Nakamoto part B, page 84
http://libgen.io/book/index.php?md5=58F4BA6022CB779AD5D0F9D0F8078E90
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