Hello Anjali,

Thank you for sharing your question with the RG community.

Unfortunately, you give us very little information about the nature of your sample. From my experience, IR and TGA are not ideal methods to confirm the assumed stoichiometry and the exact coordination of the central atom. You should perform an elemental analysis of the sample. However, the best method would be X-ray crystal structure analysis.

I wish you much success with your research.

However, bidentate coordinating carboxylate ligands can be identified in the IR spectrum by the two bands of their symmetric (1400-1500 cm-1) and antisymmetric (1600-1700 cm-1) COO modes.

Well, as said by Florian Morsbach, TGA is definitely not going to help you in that case and I agree with him about the IR spectrum.

I would also suggest you to perform a 13 NMR analysis in order to evaluate the C from the acetate group that usually is on 180 ppm chemical shift peak. Through this peak you can confirm that you have an acetate group at least.

C=O stretching band locates at 1750 cm-1 and the C–O stretching band locates around 1000-1300 cm-1. Also the intensity of these bands gives a semi quantitative information about the molar ratio.

Dear Anjali,

As Florian mentioned, it is not easy to state an adequate answer based on limited data. Please can post a chemical structure?

I agree with Matheus, concerning specificity there are only 2 posisbilities: IR or NMR; XRD does not provide any molecular specificity at all. But you might get the periodicity, if (and only if) a somehow periodic structure will be formed.

(1) You might start with IR/NMR measurements using a series of different L:M ratios starting from 0. Then, you can assign which peak belongs to imidazole, which to imine, and which to the rest.

(2) If you increase the L:M ratio, new (IR) peaks will appear due to binding. Most like they will arise at a lower frequencies/wavenumbers than the corresponding peaks from the unbound moieties. However, there might be exceptions. In most cases stretching vibrations undergo a redshift due to binding, whereas deformation vibrations undergo a blue shift.

(3) After you have the peak assignment you can study the ratio of the peak areas in dependence of the L:M ratio. I expect that particular sturture of coordination strongly depends on the L:M ratio.

I compiled some examples of IR measurements focused binding.

(1) Article Charge Transport and Glassy Dynamics in Polymeric Ionic Liqu...

(2) https://pubs.rsc.org/en/content/articlehtml/2020/sm/d0sm00337a

(3) Article Role of Mixed Solvation and Ion Pairing in the Solution Stru...

(4) https://pubs.rsc.org/en/content/articlelanding/2017/CP/C6CP07215A#cit44

(5) Article Li+ Ion Solvation in Propylene Carbonate Electrolytes Determ...

It might be that not all publications are exactly dealing with imidazole or imine, but you will definitely find instructions and band assingments. Look also in the reference there. Remember temperature changes affect the binding equilibrium somewhat comparable than changing the L:M ratio.

Best regards