Co-crystal of nadifloxacin with oxalic acid

The 2:1 co-crystal of nadifloxacin [systematic name: 9-fluoro-8-(4-hydroxypiperidin-1-yl)-5-methyl-1-oxo-6,7-dihydro-1H,5H-pyrido[3,2,1-ij]quinoline-2-carboxylic acid] with oxalic acid, C19H21FN2O4·0.5C2H2O4, was prepared by slow evaporation from a chloroform:acetone solvent system. Nadifloxacin belongs to the group of antibacterial drugs. The co-crystal is stabilized through an intramolecular O—H...O bond and intermolecular hydrogen bonds. It was studied by FT–IR spectroscopy, differential scanning calorimetry and X-ray diffraction. Hirshfeld surface analysis indicated that the major contribution to the packing is from O...H/H...O interactions.