부산대학교 도서관

A second, monoclinic, polymorph of 2-hydroxy-5-nitrocyclohepta-2,4,6-trien-1-one (shortly 5-nitrotropolone, CHNO) has been found and structurally characterized. In addition, the structure of the triclinic form has been redetermined at low temperature. Single crystal X-ray diffraction measurements showed that the title compound can crystallize either with two molecules in the asymmetric unit in the space group $$P\bar 1$$ (polymorph I) or respectively with one molecule in the space group P2/ n (polymorph II). The molecular structure of both polymorphic forms are very similar but their crystal structure displays different packing. In the crystals, neighbouring molecules are linked into dimers by the bifurcated O-H⋯O hydrogen bonds. Moreover, the crystals are stabilized by N-O⋯π, O-H⋯π, π⋯π and O⋯O interactions. Some comparisons with the crystal structure of 7-nitrotropolone isomer are also given. [ABSTRACT FROM AUTHOR]