The observation of both S-H...S and S-H...O hydrogen bonds in the room temperature disordered Form I is also reflected in the structure of Form II, which is a monoclinic structure with two independent molecules in the unit cell. The two independent molecules differ in the N-C-C-S dihedral angle, one molecule shows a gauche conformation (g+) with an angle of 74.4 • (which is similar to that seen in Form 1). The other molecule is in a trans configuration (t) with an angle of -170. At pressures above atmospheric pressure two further polymorphs have been determined. Form III forms above 1.8 GPa and was found to be stable to at least 4.2 GPa. Like Form I, it has a single molecule in the asymmetric unit but with a gauche (g-) N-C-C-S dihedral angle.