*3.2. Mechanochemical Synthesis*

Mechanochemistry has proved to be a powerful tool to obtain multi-component solid forms (salts, cocrystals, hydrates/solvates and their respective combinations), particularly in searching for new solids involving pharmaceuticals [38–41]. Cocrystallization of FUR with the corresponding coformers was carried out using various stoichiometries (1:1, 1:2, and 2:1). The patterns obtained by grinding different molar ratios of the two components were compared with the patterns of isolated API and coformers. The comparison shows that all three ratios have common characteristic peaks that were different from the two APIs. The 1:2 and 2:1 FUR:coformer patterns also contained peaks characteristics to one of the components (Figure S1, in Supplementary Materials). Only the 1:1 products had a completely different pattern where all reflections of the reagents disappeared completely, thus revealing new phases. These polycrystalline materials were used for further recrystallization to obtain suitable crystals for structure determination. In addition, there is a good agreement between the experimental and the simulated patterns (Figures S2 and S3). This synthetic approach prevented the risk for solvate formation in the case of FUR-PRX. An acetone solvate was reported previously [31] as having been obtained from acetone solution of a 1:1 stoichiometric mixture of FUR and PRX by slow evaporation.
