3.2.3. Thermal Properties

The thermal behavior of the DPA:TA was measured by DSG and TG. DPA:TA salt, exhibits a sharp, single endothermic peak at around 181 ◦C, corresponding to melting point of salt in DSC (Figure 9). It has been reported that there are two melting points of DPA; a low-melting type crystal (85–87 ◦C) and a high-melting type crystal (95–98 ◦C) [12], and TA melted with sublimation at around 350 ◦C [23–25]. DPA:TA showed a different melting point from each starting materials, suggesting that DPA:TA is a novel salt. TG data of DPA:TA revealed that there was no weight loss before melting, which confirmed the absence of any solvent or hydrate in the crystal lattice, as per the single crystal data. **(b) Figure 8.** FT-IR spectra, (a) 4000–400 cm<sup>−</sup>1 and (b) 1800–1200 cm–1, of commercial DPA, TA, DPA:TA salt obtained from slurry method and DPA:TA salt obtained slow evaporation method. **Commented [M3]:** please change the hyphen into minus. **Commented [FT4R3]:** All is minus.

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*Crystals* **2021**, *11*, x FOR PEER REVIEW 2 of 2

**(a)** 

**Figure 9.** DSC (solid line) and TG (dashed line) profiles of DPA:TA salt obtained slow evaporation **Figure 9.** DSC and TG profiles of DPA:TA salt obtained from the slow evaporation method.
