Pefloxacinium methanesulfonate 0.10-hydrate

The crystal structure of 4-(3-carboxy-1-ethyl-6-fluoro-1,4-di­hydro-4-oxo-7-quinolyl)-1-methyl­piperazinium methane­sulfonate 0.10-hydrate, C17H21FN3O3+·CH3O3S−·0.10H2O, contains pefloxacinium cations, methane­sulfonate anions and a partially occupied water of solvation. The quinoline ring system in the cation is essentially planar. The anions lie parallel to each other about inversion centers. The structure is stabilized by strong hydrogen bonds involving the terminal piperazinyl-N atom of the cation and an O atom of the anion [N⋯O 2.739 (2) Å], and a strong intramolecular hydrogen bond between carbonyl and carboxyl groups [O⋯O 2.523 (2) Å].