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I'm not sure what you're supposed to say. The IR spectra are different because, first of all, the Co-N stretch has been replaced by a Co-O stretch, because the Co-N bond has been replaced by a Co-O bond. I'm assuming you understand that these complexes differ because in the nitro- complex the NO2 group is bonded to the metal via the N, while in the nitrito- it's bonded through the O: http://en.wikipedia.org/wiki/Linkage_isomerism Additionally, the N-O bonds are no longer identical (since one of the Os is now bonded to the Co), so that will give you a more complex pattern of absorption in the NO2 group itself -- the stretches and bends. So the variation in the spectra make sense. You can see the only part that varies is below 1800 cm^-1, so I would guess that's the area for the NO2 spectra generally. You could look up the typical frequencies of the modes in NO2 if you need to try to identify the various bands. I don't remember where they are.
thanks man, yeah, I've researching this stuff all evening, kinda go this far. I'm also not sure what they want me to say, they didn't state anything besides compare.
Well, what I wrote above is about all you can usefully say, unless they want you to be able to analyze shifts in frequencies of absorption, and correlate it to changes in bond order. If that is the case -- if you've been doing that elsewhere -- then you can try to assign the bands. Once you do that, you will probably see some shifts in the NO stretch and ONO bend. You could then interpret that as being due to the NO bonds no longer being equivalent, and you might be able to say whether each bond gets stronger or weaker. (A weaker bond will absorb at a lower frequency.) That's pretty deep into the weeds. Depends on how much spectroscopy you're expected to know.
yeah i'm looking up some table to actually point out which peak represents what, thanks for clearing stuff up. i appreciate it