Enrofloxacin hydrochloride dihydrate

The asymmetric unit of the title compound, C19H23FN3O3 +·Cl−·2H2O [systematic name: 4-(3-carboxy-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinolin-7-yl)-1-ethylpiperazin-1-ium chloride dihydrate], consists of two independent monocations of the protonated enrofloxacin, two chloride anions and four water molecules. In the cations, the piperazinium rings adopt chair conformations and the dihedral angles between the cyclopropyl ring and the 10-membered quinoline ring system are 56.55 (2) and 51.11 (2)°. An intramolecular O—H⋯O hydrogen bond is observed in each cation. In the crystal, the components are connected via O—H⋯Cl, N—H⋯Cl and O—H⋯O hydrogen bonds, and a π–π interaction between the benzene rings [centroid–centroid distance = 3.6726 (13) Å], resulting in a three-dimensional array.


Comment
Enrofloxacin is a synthetic antimicrobial agent that belongs to the group of synthetic 6-fluoroquinolones (Sárközy, 2001).
Essential for the broad spectrum and the excellent antimicrobial efficacy is the fluorine substituent at position C6 and the piperazine ring at C7. The development of pharmaceutical derivatives of active principles such as salts, represent extensions of chemical space wherein enhanced or new chemical and physical properties may lead to extended use of a given drug as a therapeutic agent. Hence, the aim of this trial was produce enrofloxacin hydrochloride salt in order to improve its pharmacokinetic behavior (Sumano & Gutierrez, 2013).
The title compound crystallizes with two independent monocations (A and B) of the enrofloxacin protonated (EnrH + ), two chloride anions and four water molecules solvent (Fig. 1)  (13) Å. Bond lengths are in normal ranges (Allen et al., 1987) and to previously reported (Yamuna et al., 2014). The dihedral angles between the mean planes of the cyclopropyl ring and the 10-membered quinoline ring are 56.55 (2) and 51.11 (2)° for A and B molecules, respectively.

Experimental
The enrofloxacin hydrochloride crystals (Sumano & Gutierrez, 2013) were formed after one month by slow evaporation at room temperature from saturated solution in a mixture of water-ethanol-acetone (3:2:1). Single crystals for X-ray

Refinement
H atoms of the hydroxy groups and the amine groups were located in a difference map and their positions were refined with bond-length restraints of O-H = 0.86 (2) Å and N-H = 0.92 (2) Å, and with U iso (H) = 1.5U eq (O) and 1.2U eq (N). H atoms attached to C atoms were placed in geometrically idealized positions, and refined as riding on their parent atoms, with C-H distances of 0.95-1.00 Å, and with U iso (H) = 1.2U eq (C) or 1.5U eq (C methyl ).

Figure 1
The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as circles of arbitrary size. Intramolecular O-H···O hydrogen bonds, intermolecular hydrogen bonds forming the R 4 2 (8) and C 3 2 (17) motifs and a ππ interaction between A and B molecules.