Two polymorphic forms of the oxathiin systemic fungicide active carboxine.

Two polymorphic crystal forms of the title compound, CHNOS (systematic name: 6-methyl--phenyl-2,3-di-hydro-1,4-oxathiine-5-carboxamide), were isolated from a truncated, (12 solvent), polymorph screen on pure lyophillized material. Crystals of form 1 were obtained from all solvents included in the screen with the exception of methanol. As isolated from aceto-nitrile the crystals are triclinic, space group with = 2. Crystals of form 2, which were isolated from methanol only are monoclinic, space group 2/ with = 1. The crystal packing in both structures is dominated by the formation of infinite -NH⋯O hydrogen-bonded chains through the carboxamide core.