*2.3. Preparation of Salts and Crystallization*

Enrofloxacin and various acids in equal molar ratios were dissolved in a mixed solvent in a 50-mL conical flask, and this mixture was stirred at 50 ◦C until a completely clear solution was obtained. The solution was then allowed to slowly evaporate at room temperature to obtain single crystals of the products. Diffraction-quality crystals were obtained within 1–5 days. Each sample was scaled up 20 times for the solubility determination.

Enrofloxacin Tartrate Trihydrate (**2**): A 1:1 mixture of enrofloxacin (460 mg, 1.28 mmol) and tartaric acid (180 mg, 1.28 mmol) was added to 12 mL of a water/ethanol/dichloromethane mixed solvent (4:7:3 *v*/*v*/*v*) for crystallization. Then, **2** was obtained by filtration and drying in air (yield: 76%).

Enrofloxacin Nicotinat-EtOH Salt Solvate (**3**): A 1:1 mixture of enrofloxacin (230 mg, 0.64 mmol) and nicotinic acid (83.7 mg, 0.64 mmol) was added to 5 mL of an ethanol/dichloromethane mixed solvent (3:2 *v*/*v*) for crystallization. The resulting **3** crystals were filtered and dried in air (yield: 86%).

Enrofloxacin Suberate-2EtOH Salt Solvate (**4**): A 1:1 mixture of enrofloxacin (230 mg, 0.64 mmol) and suberic acid (110 mg, 0.64 mmol) was added to 4 mL of an ethanol/dichloromethane mixed solvent (1:1 *v*/*v*) for crystallization. Crystals were then obtained by filtration and drying (yield: 77%).
