A monoclinic polymorph of cysteamine hydrochloride

The title compound (systematic name: 2-mercaptoethanaminium chloride), C2H8NS+·Cl−, the hydrochloride salt of cysteamine, in contrast to the previously reported triclinic polymorph [Kim et al. (2002 ▶). Polyhedron, 21, 225–228], crystallized in the monoclinic crystal system. In the crystal, the cysteaminium cations are linked to the chloride anions via one S—H⋯Cl and three N—H⋯Cl hydrogen bonds. Two-dimensional slab-like networks are formed, which are stacked in [100]. This arrangement is similar to that observed in the triclinic polymorph.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: IS2503).
A monoclinic polymorph of cysteamine hydrochloride S. Ahmad, M. A. Shaheen and H. Stoeckli-Evans

Comment
The crystal structure of the triclinic polymorph, (I), of the title compound has been reported previously (Kim et al., 2002).
Those crystals were prepared by recrystallization of cysteamine hydrochloride from hot alchohols, such as n-butanol, 2-propanol or n-propanol.
The stucture of the monoclinic polymorph, (II), is illustrated in Fig. 1, and the geometrical parameters are available in the Supplementary Information and the archived CIF. Here the crystalline sample received from the producers was used without further recrystallization. In contrast to (I), that crystallized with two independent molecules per asymmetric unit, polymorph (II) crystallized with one independent molecule per asymmetric unit. The conformation of the cation (i.e. torsion angle S-C-C-N) is similar in the two polymorphs: 61.49 (16)° in (II), and -60.28 and 60.65° in (I).
In the crystal of (II) the cysteaminium cations are linked to the chloride anions, via one S-H···Cl and three N-H···Cl hydrogen bonds (Table 1). Two-dimensional slab-like networks are formed, which stack in the [100] direction (Fig. 2). A similar hydrogen-bonded slab-like arrangement was also observed in the crystal structure of the triclinic polymorph (I), see Fig. 3.

Experimental
The sample used, supplied by Alfa Aesar (A Johnson Matthey Company) USA, consisted of colourless block-like crystals.
A small piece of a large crystal was used for data collection.

Refinement
The H-atoms were all located in a difference electron-density map and were freely refined: S-H = 1.21 (3) Fig. 1. A view of the molecular structure of the title compound, with the displacement ellipsoids drawn at the 50% probability level.  Table 1 for details). Fig. 3. A view, along the a axis, of the crystal packing in the triclinic polymorph of the title compound (Kim et al., 2002). The S-H···Cl and N-H···Cl hydrogen bonds are shown as dotted cyan lines.  (6)