[Damian]

Hi guys,
I have a problem with assigning the peaks in my IR spectra to the compounds I made. It’s for a report I have to hand in, but the deadline has passed and I can’t go back to the prof for these questions . I’m not good at assigning IR spectra so I really hope you could help me out with this.

It’s about these two nickel complexes: [Ni(NH3)₄(NO2)₂] and [Ni(C5H5N)₄(NO2)₂]
I tried to look for the exact reference spectra in IR database books, I’ve spent many hours on SciFinder, but I can’t find any reference spectra. But I have found spectra of similar compounds on SciFinder, most important one is [Ni(NH3)6]Cl2 .

When you have a look at my spectra you see that they have many peaks in common.

On both:
1205/1206
1336/1350 (pretty close so the same, right?)
(1606+1653)/(1611+1640) (looks the same to me)
3347/3379

So this means that for the ‘blauw’ (=blue) compound (which should be the nitro/pyridine one) the characteristic peaks are the 1448, the 693 and the 3347 which is a lot broader

On NIST I’ve found the spectra of pyridine and the peak at 1448 and at 693  can be assigned to pyridine.

For the ‘paars’  (=purple) compound (which should be the nitro amine one) the only characteristic peaks is 1293. And I can’t explain it.

If I look at the spectra of the [Ni(NH3)6]Cl2 I see a lot of peaks which are in the purple compound, but they are also in the blue compound (where they shouldn’t be).

And also the characteristic 1350 and 1530 nitro peaks which should be in both of the compounds are not there at all! Only a 1350 peak in the purple compound. Do I even have NO2 in my products??

As a conclusion, I have no idea if my synthesis was successful or not.

Help will be much appreciated!

[Damian]

anyone? 

[Arkcon]

OK, I'm hardly an expert on IR, particularly not for inorganic co-ordination compounds, however:

When you have a look at my spectra you see that they have many peaks in common.

On both:
1205/1206
1336/1350 (pretty close so the same, right?)
(1606+1653)/(1611+1640) (looks the same to me)
3347/3379

I'm not seeing enough similarity on the 1336/1350 peaks.  They seem to have different widths, that may mean a different functional group is responsible for the peaks.  The (1606+1653)/(1611+1640) peaks also look to different to me to make a conclusion.  Your samples are likely contaminated with a reaction product or reactant that you should try to identify.