59Co(II) is paramagnetic. Therefore, its complexes cannot be observed on 1H NMR or on 59Co NMR. Despite that 59Co is quadrupolar  with a spin number of 7/2 (100 % abundance), Co(III), Co(I) and some Co(0) complexes can be studied both with 1H NMR and 59Co NMR (the latter giving broad lines up to 20 kHz) but in a very large chemical shift range (~20000 ppm). The strongly quadrupolar nature of Co (in not paramagnetic complexes) probably disturbs 2JCo,H and 3JCo,H couplings in the 1H NMR.

I don't have examples of that right now, but more than 10 years ago, I ran samples of Co complexes. The proton signals of the ligands showed complex coupling patterns (with big J values) and I found signals as far as 150 ppm.

I think trying to grow single crystals and get an X-ray crystal structure might be more helpful than NMR in this case. Mass spectroscopy might help you see a molecular ion which may also be helpful. Best of luck.

Thanks a lot for all of you  Dr. Imre Tóth , Dr. José R. Martínez, Dr. Melanie Pilkington i really appreciate your contributions.

Actually i have the single crystals of the two complexes, but i need to follow them in a reaction with HNMR. The problem is that one of the two complexes showed good HNMR and the other one almost didn't show any peaks in HNMR.

 So what could be the reason behind this or what we can get from this information?

Kind Regards

As I wrote above Co(II) is paramagnetic. So if you have a Co(II) compound you won't get any NMR signals. If you can get a good 1H NMR from one of your complex and you are sure that Co is present in it, that should be a Co(III)-, Co(I)- or perhaps Co(0)- complex.

It depends on how far the protons are from the Co center, since there is an inverse cubic relationship. The further away, the less the influence of the paramagnetism on the chemical shift position. If one in any event records the spectrum over a very broad spectral range (+-400 ppm) at a high enough concentration, one should see everything. The challenge is - if it is not very very pure (>99 %) and contaminated with diamagnetic impurities, the spectra tend to look awful, due to the different relaxation times. So, Go for a very pure and concentrated sample, and you should readily see everything. You can even calculate the chemical shift positions with some advanced DFT packages... We have done so for an open shell Nickel complex (see Organometallics, 2013).

I would like to add to the previous statements and reiterate a couple points. Make sure you collect a spectrum using a broad sweep width. This is important because if the signals are very broad (which may be the case since you do not see any peaks), it may not be apparent if there are fold-over signals from outside the spectral range. Be sure to work with samples of adequate concentration (I am guessing ~10 - 20 mM should be fine). You will want to also increase your number of transients compared to a diamagnetic spectrum. For instance, if you usually collect a spectrum in 2 minutes, try spending 10-20 minutes for a paramagnetic spectrum. The peaks for paramagnetic complexes can be broad or sharp, which may depend on a number of factors, but different ligand donors, how fluxional or rigid the molecule is in solution on the NMR timescale, and spin state all influence the appearance of the spectrum. I have seen Co(II) complexes with sharp peaks and with broad peaks. After Fourier transform and phasing of the spectrum, try increasing the intensity of the spectrum and you may see very broad peaks become visible.

As mentioned by others the spectrum will be very broad but it may be possible to get one. Some examples can be found in Dalton Trans,  2011, 40, 1313 which details the NMR of Co(II) complexes, [TpPh2Co(dtc)].

It is possible to get 1H NMR of Cobalt complexes even though it is Co(II), which is paramagnetic. I have 1H NMR of my own Co(II) complex with Tp ligand, but the chemical shift is very large. Like Dr Harding said, check Co complexes with Tp ligands. The person who works with these kind of complexes is Dr David Tierney of Miami University in Ohio. Reading some of his papers might be helpful.

Dear Burgert, Sarina, David and Lava,

Alright, you are all right. Above, I meant using the usual shift range and setup of 1H NMR (0-15ppm) or someone who is that familiar changing sweep widths or other parameters on the NMR. It also matters of course, what kind (size) of Co(II) complex is present. Here are some more references and approaches to paramagnetic NMR spectroscopy.

Regards,  

                    Imre 

Thanks a lot for all for their fruitful contribution and guide

I will try to run the sample again with a broad sweep width and see what might happen

Some of us including me have ignored the second part of your question, i. e. your Co(II) complex is based on a functionalized triazole. Such a ring itself contains very few H-s to detect, which are probably in the very close vicinity of the paramagnetic Co. If you have spacious H-containing substituents (alkyl, aryl etc.) on your triazole that is another story (facilitation) for 1H NMR.

Thanks Dr Imre

Yes the triazole ring is susbstituted at 1-position with Mesityl group and the protons from the three methyl groups are very clear in 1HNMR in one complex but in the other complex is not clear at all and this was my question what could be the reason behind the diffrent behavior of the two complexes (one has two ccordinated water molecules and the other has two methanol molecules, this is the only diffrence between the two complexes).

Thanks Dominik 

But the complex has coordinated water, so i think  if i oxidize it the structure might change and coordinated water convert into OH or =O, I am not sure this will be helpful or not? we wait comments on this point.

Dear Hussein,

Do you mean then that the aqua complex is not detectable on 1HNMR? What is your deuterated solvent? Can you exclude exchange or other chemistry upon dissolution of your complex?

Regards,   Imre

Thanks a lot for all of your contributions,  now i have another question regarding the same complex :

If i have a diunclear Co(II) complex it would be paramegnetic or diamagnetic ? and so i can expect it would give peaks in NMR or not?

Thanks in advance

There are quite some examples that dinuclear Co(II)-Co(III) complexes can be diamagnetic. Dinuclear Co(II) complexes can also be diamagnetic see for example https://books.google.hu/books?id=Owuv-c9L_IMC&pg=PA242&lpg=PA242&dq=dinuclear+Co+complex+diamagnetic&source=bl&ots=zXr__qlPk9&sig=maIPrQgR5_72kpEBTqs8ctFVMms&hl=en&sa=X&ved=0CDwQ6AEwA2oVChMIo9OMyIuMxgIVRNUUCh3ufQA2#v=onepage&q=dinuclear%20Co%20complex%20diamagnetic&f=false but this seems to be much less frequent. If you have triazole ligands with Co(II) the same applies what already is discussed above.