Dear Srividya

That's possible in few cases on neutral coordination. But still to confirm strongly you can proceed with multinuclear NMR techniques like 17O, 33S, 15N, 31P etc. depend on the donating atom.

Dear Srividya Swaminathan it's difficult to give you a helpful answer as your question is rather unspecific. It would be very helpful if you could specify what your ligand is and which metal you used. For example, if the protons of the ligand are far away from the coordinating donor atom, it may well be that the changes in the NMR spectra are small.

Respected Frank T. Edelmann Sir, I am using acylthiourea complex with ruthenium metal ion. The metal is coordinated with sulphur ion.

Dear Srividya Swaminathan thanks for the information. This confirms more or less what I suspected. The Ru center is three atoms away from the first hydrogens. Thus it could well be that there are only little changes in the NMR spectra upon coordination. Did you check out some literature references on related complexes? If not, see references cited below and attached article.

Article Cytotoxicity of ruthenium-N,N-disubstituted-N′-acylthioureas complexes

Article Selective Coordination Mode of Acylthiourea Ligands in Half-...

Article Unusual coordination mode of aroyl/acyl thiourea ligands and...

If the complex is diamagnetic then the signals chage little,but if the complex is paramagnetic then signals willl shift very much you may get large shift like 100 ppm or more and also -20ppm..

It is possible. If everything is set up correctly (referenced correctly), depending on the ligand,, only a slight shift might appear. But slight is real- what is "slight"?

Keep in mind the magnitude of this shift is because of the bond strengths and electron densities of the complex - could be weak, or a few atoms away, I don't know the molecule.

I agree with David A. Aubry and Arghyadip Bhowmik . Apparently all such ruthenium(II) arene complexes are diamagnetic. Moreover the first hydrogen atoms (i.e. the –NH protons) are three atoms away from the ruthenium center. Accordingly, in the Organometallics paper which was attached to my last answer, the authors write explicitely about the 1H NMR spectra:

"In the 1H NMR spectra of the complexes , the carbonyl- and thiocarbonyl-attached N−H and thiocarbonyl-attached N−H protons were observed as singlets and doublets around 10.80− 11.13 and 11.42− 11.81 ppm, respectively. The new signals observed in the regions 1.27−1.30, 2.24−2.98, and 5.23−5.42 ppm indicate

the presence of a p-cymene moiety in the complexes. All other chemical shift values of the complexes were very similar to those of the free ligands."

Srividya Madam,

It is quite fortunate with the metal complexes. As per my knowledge, there should be shift in ppm values of peaks (small or large).

Firstly confirm the progress of the reaction from ligand to complex through simple techniques like comparing the melting points. Sometimes you may fail to detect the changes in NMR due to some of the factors like recording NMR of compound repeatedly with different NMR instruments (200, 300, 400, 500 MHz ranges). All that you have to do is to go through the corresponding literature and compare with the values already present if any. I also would like to suggest you to take multinuclear NMR and variable temperature NMR since there is a chance of stability related issues because of the bonds strength and electronic properties of the complex. If it is new or novel, crystal XRD gives you the right information (provided if you could re-crystallize it). Or else go with mass, ICP-OES or SEM-EDX analyses.

Dear Srividya,

In order to confirm the presence of the complex, I suggest you make an FTIR spectrum. The signals of the coordinated ligand should shift respect to the uncoordinated molecule.

Of course, it is possible, but the shifting of the signals depends from the concrete ligand and metal cation.

Srividya Swaminathan I think that Marcella Balordi added a very good point. In the FTIR spectra, especially the C=S stretching frequency should change significantly upon coordination to ruthenium.

Thank you Marcella Balordi Frank T. Edelmann for your suggestion. I do have confirmed via other spectroscopic methods such as IR Mass and XRD the formation of the complex. However, taking the NMR in DMSO-d6, I as mentioned observed no changes in the ligand signals of the complex. So the question arises if the complex separated into its constituents (Metal precursor + Ligand) in the solvent? Although, i see the Literature NMR data of the metal precusor is almost similar to the one obtained in my complex, but both involve eta-6 coordination of the arene ring to ruthenium and hence I am not able to conclude. I believe I need to verify with NMR in different solvents.

Srividya Swaminathan, yes, I think for your NMR experiments you should also try other solvents than DMSO-d6. Chances are that DMSO-d6 could replace your ligands. You should perhaps try acetone-d6 ior CD2Cl2 which are less coordinating solvents.

I agree with Frank T. Edelmann . The DMSO is a coordinating solvent with good affinity to Ruthenium so it may replace your ligand.

Thanks a lot..Frank T. Edelmann Marcella Balordi

If you are not sure, do DOSY experiment of your complex. You mentioned that you have also the signals of the metal precursor. If all the signals have the same diffusion coefficient, you have your complex.