Dera Ramandeep Kaur Mankoo generally this depends on whether the used transition metals are diamagnetic or paramagnetic. Only complexes of diamagnetic transition metal ions will give you good NMR spectra.

I agree with Frank T. Edelmann

NMR spectra are not preferred for characterization of transition metal complexes which depends up on whether the complex is paramagnetic or dimagnetic as mentioned by Frank T. Edelmann. For the characterization of the metal complexes UV-Vis spectra are used . Depending upon types of transition , one can draw the conclusion about the geometry of the complexes.

I think part of it is due to the fact that complexes often don't have many NMR active nuclei (and as mentioned above could also be paramagnetic). Ligands will often give much the same NMR spectra whether they are bound or unbound to the metal centre. On the other hand IR will show a characteristic metal ligand stretch, and other IR bands will change frequency on complexation.

I forgot to add that IR can be done on solid samples. For NMR it will typically be done in solution and often complexes are not soluble in common NMR solvents. Plus the problem that the ligands may well drop off in some solvents.

Thanks David Stephenson!

Thanks Frank, Aravind and Madhukar!

Dear Ramandeep Kaur Mankoo you're welcome. If you want more specific answers you should perhaps mention in more detail which metals and ligands you are using,

Complexes of the lanthanide elements (Ln) often give interpretable NMR spectra although most Ln3+ ions are paramagnetic.

Prof. Frank, we are using substituted hydroxycinnamic acids (p-coumaric acid, ferulic acid) as ligands for complexation with transition metals (paramagnetic).

Dear Ramandeep Kaur Mankoo thank you for sharing this information. In that case you have to rely mostly on other characterization methods.

As already mentioned by other authors, many internal transition and transition metal coordination complexes are paramagnetic systems and cannot be addressed by diamagnetic NMR spectra. It is necessary to use the parameters and the NMR approach of paramagnetic systems since fundamentally there is a displacement of signals and the spectral window must be larger and on the other hand the signals are broadened as a function of the distance to the paramagnetic center, Solomon's equation .