2.2.1. Slow Evaporation Method

*2.2. Crystallization of DPA:TA Salt* 2.2.1. Slow Evaporation Method For X-ray single-crystal structure analysis, DPA (0.5 mmole) and TA (0.5 mmole) in a 1:1 molar ratio were ground in a mortar and pestle for 10 min to obtain a fine powder, then a few drops of ethanol were added to it, before grinding again for 10**–**15 min to obtain a powder. From this, 50 mg was used for the crystallization experiment. Colorless single crystals suitable for single crystal X-ray diffraction were obtained by dissolving the 50 mg For X-ray single-crystal structure analysis, DPA (0.5 mmole) and TA (0.5 mmole) in a 1:1 molar ratio were ground in a mortar and pestle for 10 min to obtain a fine powder, then a few drops of ethanol were added to it, before grinding again for 10–15 min to obtain a powder. From this, 50 mg was used for the crystallization experiment. Colorless single crystals suitable for single crystal X-ray diffraction were obtained by dissolving the 50 mg of ground material in 15 mL acetonitrile and 5 mL ethanol under sonication at a temperature of 50 ◦C for 1h. The resulting solution, obtained after filtration, was left for slow evaporation at ambient conditions for 4–6 weeks to obtain a long plate-like crystal, which was stuck on the wall of the flask.

#### of ground material in 15 mL acetonitrile and 5 mL ethanol under sonication at a 2.2.2. Slurry Method

*2.3. Single-Crystal X-ray Diffraction*

solid form.

temperature of 50 °C for 1h. The resulting solution, obtained after filtration, was left for slow evaporation at ambient conditions for 4**–**6 weeks to obtain a long plate-like crystal, which was stuck on the wall of the flask. 2.2.2. Slurry Method Reproducing the salt crystal was found to be difficult, so another method for crystallization was used. Luckily, similar solid salt is easily obtained by the slurry method. One mmole each of DPA and TA were weighed at a molar ratio of 1:1 and suspended in Reproducing the salt crystal was found to be difficult, so another method for crystallization was used. Luckily, similar solid salt is easily obtained by the slurry method. One mmole each of DPA and TA were weighed at a molar ratio of 1:1 and suspended in 50 mL acetonitrile in a 250 mL conical flask. The resulting suspension was stirred in a magnetic stirrer at 25 ◦C, 500 rpm for about 36 h until a white solid material precipitated out. The resulting suspension was filtered to isolate the white solid, which was then air dried for 5–6 days at ambient conditions before being used for further analysis. Powder X-ray diffraction (PXRD) patterns of the isolated solids matched the simulated PXRD pattern obtained from single crystal data DPA:TA, suggesting that both were the same solid form.

#### 50 mL acetonitrile in a 250 mL conical flask. The resulting suspension was stirred in a *2.3. Single-Crystal X-ray Diffraction*

magnetic stirrer at 25 °C, 500 rpm for about 36 h until a white solid material precipitated out. The resulting suspension was filtered to isolate the white solid, which was then air dried for 5**–**6 days at ambient conditions before being used for further analysis. Powder X-ray diffraction (PXRD) patterns of the isolated solids matched the simulated PXRD pattern obtained from single crystal data DPA:TA, suggesting that both were the same The single-crystal X-ray diffraction data for DPA:TA salt was collected at 93 K. The measurements were carried out in ω-scan mode with an R-AXIS RAPID II (Rigaku Co., Tokyo, Japan) with the Cu-Kα X-ray obtained from rotating the anode source with a graphite monochromator. The integrated and scaled data were empirically corrected for absorption effects using ABSCOR [17,18]. The structures were solved by direct methods using SHELXS and refinement was carried out by full-matrix least-squares technique using SHELXL [19,20]. All non-hydrogen atoms were refined anisotropically. The hydrogen atom

measurements were carried out in ω-scan mode with an R-AXIS RAPID II (Rigaku Co., Tokyo, Japan) with the Cu-Kα X-ray obtained from rotating the anode source with a attached to the nitrogen N2, N3, and O4 atoms in the DPA:TA salt were located using the differential Fourier map and refined isotropically. All other hydrogen atom positions were calculated geometrically and included in the calculation using the riding atom model.

The molecular figures were produced and prepared using Mercury 4.1.0 software [21]. CCDC 2065287 contains the supplementary crystallographic data for the DPA:TA salt and can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data\_request/cif (accessed on 28 March 2021).
