Perhydrobenzimidazole-2-thione

The studied crystal of the title compound, C7H12N2S, is a racemic mixture of two isomers, viz. S,S and R,R. The two isomers share the same position on a mirror plane in the space group P21/m; thus all atoms except one are disordered between two positions in a 1:1 ratio. Intermolecular N—H⋯S hydrogen bonds link the molecules into chains propagating in the [010] direction.

The title molecule consists of one thioimidazole five-membered ring and one six-membered ring which display chair conformation. The studied crystal is a racemic mixture of two isomers -(S,S) and (R,R), respectively -which share the same position on a mirror plane in space group P2 1 /m, thus all atoms except one are disordered between two positions in a ratio 1:1. In the crystal, intermolecular N-H···S hydrogen bonds (Table 1)

Experimental
The title compound was prepared according to the reported method (Allen et al.,1946). Crystals of (I) suitable for X-ray data collection were obtained by slow evaporation of a CH 2 Cl 2 and MeOH solution in a ratio of 4:1 at 293 K.

Refinement
All H atoms were geometrically positioned (C-H 0.97-0.98 Å, N-H 0.86 Å) and refined as riding, with U iso (H) = 1.2 U eq (C, N). The crystal structure was refined in two space groups -P2 1 and P2 1 /m, respectively. In both groups the severe disorder has been observed with almost identical values of final R-factors, so the preference has been made for P2 1 /m. Fig. 1. View (S,S)-isomer of (I) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.