Steam
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Registered: 25-3-2014
Location: Minnesota
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Mood: Triple Point
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Need help with IR determination of tautomerization of a Cu(II) ligand.
Hello, I am currently trying to figure out what is happening with this ligand when it complexes with a Cu(II) salt. The bottom spectrum is salicylhydroxamic acid (SHA) and the top spectrum the filtered and dried precipitate when Cu(II) sulfate solution is mixed with a solution of SHA.
The biggest differences that I see is the loss of the peak at 3270 cm^-1 and the loss of the peak at 1630cm^-1. It is to my knowledge that these two
peaks represent the N-H stretch and the C=O group. It has been found from past ESR studies that hydroxamic acid groups chelate to Cu(II) salts with
the two oxygen groups.
My guess is that the amide is tautomerizing to the imidic acid form as it chelates to make the carbonyl oxygen more electronegative. If that is the
case there would be a C=N group show up. There is a more prominent peak at 1591, could this be the C=N group.
Does any of this sound reasonable? Thoughts?
Thank you for any help in advanced! 
Attachment: SHA Cu(II) SHA peaks.TIF (3.1MB)
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Metacelsus
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Posts: 2531
Registered: 26-12-2012
Location: Boston, MA
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Mood: Double, double, toil and trouble
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I think the main difference would be loss of the acidic proton upon binding to the copper. Can you get a spectrum of the sodium or potassium salt of
your hydroxamic acid? This would allow you to distinguish the effects of deprotonation from the effects of chelation.
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