*2.8. Solubility Assays*

Thermodynamic solubility measurements were performed in an Invenio R FTIR spectrometer (Bruker) after equilibrating the solids in a 0.9% NaCl water solution [8] under stirring at 500 rpm for 24 h. After the equilibrating time, the suspensions were filtrated through a 20 μm filter, and the resulting clear solution was analysed by FTIR. Then, the solid was analysed by PXRD to study the phase stability after equilibrium, resulting for (lidhcl)2(res) and (lidhcl)2(hq) that the cocrystal form remained stable after 24 h but not for (lidhcl)2(pyr). A calibration curve was built with different (lidhcl) concentrations [18,19] obtaining linear models with *R*<sup>2</sup> values greater than 0.99, which were used to calculate the thermodynamic solubility. The peak used for the calibration curves was the area between 1712 cm−<sup>1</sup> and 1612 cm−1, corresponding to (lidhcl), where there was no interference of any coformer.
