Crystal structure of danofloxacin mesylate (C19H21FN3O3)(CH3O3S)

The crystal structure of danofloxacin mesylate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Danofloxacin mesylate crystallizes in space group P1 (#1) with a = 6.77474(8), b = 12.4973(4), c = 12.82826(28) Å, α = 84.8709(29), β = 87.7501(10), γ = 74.9916(4)°, V = 1044.723(11) Å3, and Z = 2. The protonation of the danofloxacin cations was established by the analysis of potential intermolecular interactions and differs from that expected from isolated-cation calculations. The crystal structure consists of alternating layers of cations and anions parallel to the ac-plane. There is parallel stacking of the oxoquinoline rings along the a-axis. The expected N–H⋯O hydrogen bonds between the cations and anions are not present. Each cation makes an N–H⋯O hydrogen bond with the other cation, resulting in zig-zag chains along the a-axis. Both cations have strong intramolecular O–H⋯O hydrogen bonds. There are several C–H⋯O hydrogen bonds between the danofloxacin cations and mesylate anions. The powder pattern has been submitted to ICDD® for inclusion in the Powder Diffraction File™ (PDF®).