Synthesis, crystal structure, and characterization of three novel compounds of the quinolone family member (norfloxacin)

The synthesis of three novel compounds of norfloxacin (nf) is reported. Their crystal structures are presented and discussed. The first compound, (nfH(2))Cl-2.H2O (nfH(2) = doubly protonated molecule of nf), crystallizes in the monoclinic space group P 2(1)/c with a = 8.438(2), b = 14.281(3), c = 15.012(3) Angstrom beta = 93.87(3)degrees, Z = 4. The carbonyl oxygen O(1) is protonated, and this proton is bonded via intramolecular hydrogen bond to the oxygen O(11) of the carboxylic group (O(11)...O(1) = 2.605(4) Angstrom). The terminal nitrogen atom N(24) of the piperazine group is also protonated. The positive charge of the nf molecule is neutralized by two chloride anions. The crystal structure is stabilized by numerous hydrogen bonds of the type O-H...O, O-H...Cl, N-H...Cl. The compounds (nfH(2))(nfH)[CuCl4]Cl.H2O and (nfH(2))(nfH)[ZnCl4]Cl.H2O (nfH = monoprotonated molecule of nf) are isostructural and both crystallize in P 2(1)/c. Both structures are ionic consisting of a tetrachlorometalate(II) anion and two nonequivalent, protonated nf molecules. It seems that in strongly acidic media, the proton is bonded between O(1) and carboxylic oxygen, which prevents the coordination of the metal ions to this position. The results of other measurements (TG, FT-IR, Raman spectroscopy) are also included.