*2.9. Solubility Analyses*

The solubility of these products was determined according to the shake-flask method [29]. Excess amounts (100 mg) of the crystals were added to the screw-capped glass vials containing

2.5 mL of ultrapure water, and the resulting suspensions was shaken at room temperature. After 24 h, the suspensions were filtered through 0.22-µm polycarbonate filters, and the compounds' concentrations were determined using the Agilent 1260 Infinity II HPLC system (Palo Alto, CA, USA) equipped with a 1260 Multi λ Fluorescence detector with the wavelength of the excited and emitted spectra of crystals being 280 nm and 450 nm, respectively. The C18 HPLC column (Poroshell 120 EC-C18, 4.6 mm × 100 mm, 2.7 µm) was employed, and acetonitrile, methanol and triethylamine phosphate (pH = 2.5) were used as the mobile phase (1:24:75, *v*:*v*::*v*) with a flow rate of 1 mL/min. Each solubility test was performed in triplicate. mL of ultrapure water, and the resulting suspensions was shaken at room temperature. After 24 h, the suspensions were filtered through 0.22-μm polycarbonate filters, and the compounds' concentrations were determined using the Agilent 1260 Infinity II HPLC system (Palo Alto, CA, USA) equipped with a 1260 Multi λ Fluorescence detector with the wavelength of the excited and emitted spectra of crystals being 280 nm and 450 nm, respectively. The C18 HPLC column (Poroshell 120 EC- C18, 4.6 mm × 100 mm, 2.7 μm) was employed, and acetonitrile, methanol and triethylamine phosphate (pH = 2.5) were used as the mobile phase (1:24:75, v:v::v) with a flow rate of 1 mL/min. Each solubility test was performed in triplicate.

*Crystals* **2020**, *10*, x FOR PEER REVIEW 6 of 18

Excess amounts (100 mg) of the crystals were added to the screw-capped glass vials containing 2.5

#### **3. Results and Discussion 3. Results and Discussion**

#### *3.1. Field-Emission Scanning Electron Microscopy (FESEM) 3.1. Field-Emission Scanning Electron Microscopy (FESEM)*

The FESEM (Heidelberg, Germany) images provide information about the crystal morphology of several new crystals (Figure 1). Needle-shaped or long rod-shaped forms are seen for the products **1** and **2**, whereas **3** and **4** displayed rectangular blocks and fragmentary crystals. The FESEM (Heidelberg, Germany) images provide information about the crystal morphology of several new crystals (Figure 1). Needle-shaped or long rod-shaped forms are seen for the products **1** and **2**, whereas **3** and **4** displayed rectangular blocks and fragmentary crystals.

**Figure 1.** Field-emission scanning electron microscopy (FESEM) photos of compounds **1**–**4**. **Figure 1.** Field-emission scanning electron microscopy (FESEM) photos of compounds **1**–**4**.
