A triclinic polymorph of 1,3-thiazolidine-2-thione (2-mercaptothiazoline).

A planar conformation of 1,3-thiazolidine-2-thione (TZDTH), C3H5NS2, was crystallized for the first time. The new triclinic polymorph (P\overline 1) obtained was compared in terms of its intra- and intermolecular geometry with three previous reports of a monoclinic polymorph (P2(1)/n). The packing is based on centrosymmetric dimers of TZDTH, linked by N-H.