*3.5. DSC Analysis*

The thermal behavior of coformers and cocrystals was tested using differential scanning calorimetry (DSC). The DSC heating curves and melting temperatures are represented in Figure 12.

The melting point of the cocrystals, DL-Mandelic acid and pyridinecarboxamides are listed in Table 4. **H2ma**, **pic**, **nam** and **inam** exhibit a sharp melting endotherm followed by decomposition, and do not show any phase change/transformation on heating before melting. Similarly, the (**pic**)-(**D-H2ma**) (Figure 12a), (**nam**)-(**L-H2ma**) (Figure 12b) and (**inam**)-(**L-H2ma**) (Figure 12c) binary solids exhibit melting, followed by decomposition. There is no phase change before melting on heating. The cocrystals displayed a lower melting point than the pure mandelic acid and the coformers. The thermal analysis of the cocrystals and their comparison to that of the coformers revealed that in (**1**) and (**3**) there is a direct correlation between the melting points of the coformers and the cocrystals (Table 4): the higher the melting point of the coformer, the higher the melting point of the cocrystal. However, in (**nam**)-(**L-H2ma**) this trend is broken and its melting point is the lowest of the three cocrystals, probably because the strength of the hydrogen bonds is also the weakest.

**Figure 12.** DSC analyses of the resulting powders of pure components and the cocrystals **1**, **2a** and **3**. **Table 4.** Melting points (M. p.) of coformers \* and prepared cocrystals.


\* Taken from http://www.chemspider.com/.
