Sulfapyridine (polymorph III), sulfapyridine dioxane solvate, sulfapyridine tetrahydrofuran solvate and sulfapyridine piperidine solvate, all at 173 K

The X-ray crystal structures of solvates of sulfapyridine have been determined to be conformational polymorphs. 4-Amino-N-(1,2-dihydro­pyridin-2-yl­idene)benzene­sulfonamide (polymorph III), C11H11N3O2S, (1), 4-amino-N-(1,2-dihydro­pyri­din-2-yl­idene)benzene­sulfonamide 1,3-dioxane monosolvate, C11H11N3O2S·C4H8O2, (2), and 4-amino-N-(1,2-dihydro­pyri­din-2-yl­idene)benzene­sulfonamide tetra­hydro­furan monosolvate, C11H11N3O2S·C4H8O, (3), crystallized as the imide form, while piperidin-1-ium 4-amino-N-(pyridin-2-yl)benzene­sul­fon­amidate, C5H12N+·C11H10N3O2S−, (4), crystallized as the piperidinium salt. The tetra­hydro­furan and dioxane solvent mol­ecules in their respective structures were disordered and were refined using a disorder model. Three-dimensional hydrogen-bonding networks exist in all structures between at least one sulfone O atom and the aniline N atom.