The vibrational signatures of the calcium oxalate polyhydrates are investigated using a combination of Density Functional Theory‐Dispersion corrected, Fourier Transform‐ Raman and ‐Infrared (IR) spectroscopies. Most vibrational bands were assigned and the theoretical predictions were compared with in‐house and other experimental data, for both, IR and Raman spectroscopies. Such an approach allowed a more accurate analysis of vibrational spectra helping in the completion of the band assignments of the vibrational bands of the mono, di, and tri hydrate calcium oxalate (COM, COD, and COT). Particular attention has been paid to the degree of hydration of COD, the low Raman wavenumbers, and the presence of oxalic acid in natural calcium oxalate polyhydrates. The obtained results are expected to be supportive in the detection of the different polyhydrates in natural samples, such as in kidney stones.

The MCM-41 material is very commonly used as a support for catalysts. However, theoretical investigations are significantly limited due to the lack of appropriate models that well and accurately describe the real material and enable effective computation at the same time. In this work, our aim is to obtain calculable models at the DFT level of MCM-41 which are as close as possible to the real material. In particular the hydration degree has been investigated, and we present and characterize here for the first time a model for the MCM-41 unit cell filled with explicit solvent water molecules. This is particularly important, because the models developed here are aimed to be further applied in theoretical ab initio/DFT studies of adsorption or as a support for modelling active sites in catalysts.