7-[(7S)-7-Aza-niumyl-5-aza-spiro-[2.4]hept-5-yl]-8-chloro-6-fluoro-1-[(1S,2R)-2-fluoro-cyclo-prop-yl]-4-oxo-1,4-dihydroquinoline-3-carboxyl-ate methanol monosolvate.

Sitafloxacin is a newly developed fluoro-quinolone anti-bacterial drug. The crystal studied, C(19)H(18)ClF(2)N(3)O(3)·CH(3)OH, consists of one mol-ecule of sitafloxacin and one methanol solvent mol-ecule. The mol-ecule of sitafloxacin is a zwitterion with a protonated primary amine group and a deprotonated carboxylate group. The cyclopropane ring and the CO(2) group make dihedral angles of 79.5 (3) and 35.4 (4)°, respectively, with the fused ring system. The supra-molecular structure is defined by N-H⋯O and O-H⋯O hydrogen bonds.