A monoclinic polymorph of chloro-thia-zide

A new polymorph of the diuretic chloro-thia-zide, 6-chloro-1,1-dioxo-2H-1,2,4-benzo-thia-zine-7-sulfonamide, C₇H₆ClN₃O₄S₂, is described. Crystallized from basic aqueous solution, this monoclinic polymorph is found to be less thermodynamically favoured than the known triclinic polymorph and to feature only N-H⋯O type inter-molecular hydrogen bonds as opposed to the N-H⋯O and N-H⋯N type hydrogen bonds found in the P1 form.