(3RS)-S-[1-(3-Chlorophenyl)-2-oxopyrrolidin-3-yl]thiouronium bromide

In the title molecular salt, C11H13ClN3OS+·Br−, the C—N bond lengths in the –S–C(NH2)2 fragment indicate partial double-bond character of these bonds. The constituent ions are connected by N—H⋯Br bridges into Z-shaped chains. The supramolecular architecture of the structure can be described by being composed of these chains interlocked by additional C—H⋯Br short contacts. An intramolecular N—H⋯O=C bridge, as well as weak C—H⋯O hydrogen bonds, are also present in the structure.

A further interest has been provoked by a discovery (Sedlák et al., 2002(Sedlák et al., , 2003Hanusek et al., 2004) that N-unsubstituted isothiuronium salts undergo a transformation involving only a general base catalysis whereas in the case of N,N'-dimethylisothiuronium salts such a transformation is catalyzed by both acid and base buffer components.
There is a limited number of X-ray structures of isothiouronium salts reported in the literature. Eleven of these are the compounds of the S-C(NH 2 ) 2 type with no replacement of the hydrogens that are pertinent to the -NH 2 group (e.g. Vijayan et al., 1977;Bel'skii et al., 1985;Ishii et al., 2000). The rest are the compounds where both nitrogen atoms are connected to a chain thus forming five-to eight-membered rings (e.g. Rovnyak et al., 1995;Cotton et al., 2006;Luger et al., 1996). There is only one example of a disubstituted acyclic species, N-methyl-N'-phenyl-S-sulfomethylisothiourea (L'abbe et al., 1980).
These C-N bond lengths in the S-C(NH 2 ) 2 fragment of the title structure reveal a partly double bond character of these bonds. This is in accordance with planarity of this fragment. (The groups -NH 2 were therefore duly constrained during refinement.) The interatomic angles C4-S1-C11 (104.56 (18)°) and N2-C11-N3 (122.0 (4)°) in the title compound are similar to those in the related N,N'-dimethyl derivative (98.75 (18)° and 122.6 (4)°, respectively) and also fall into the literature range which is 99.2-105.5° and 108.0-123.5°, respectively. The twist angles about the N1-C5 bonds, which show a mutual orientation of both rings, are 7.8 (1) and 29.7 (1) ° in the title compound and its N,N'-dimethyl derivative, respectively.
All the known isothiouronium cations reveal hydrogen bonding in the crystal structure. Also in the packing of the molecules of the title compound and its N,N'-dimethyl derivative such interactions are present. All the NH 2 hydrogen atoms are donated to the bromine atoms except for H3AB. Those with the shortest Br···H distances form infinite chains via the supplementary materials sup-2 N2-H2AB···Br···H3AA-N3 motifs (Figs. 2 and 3; Tab. 1) with the angle H2AB···Br1···H3AA equal to 100.7 (1)°. There is also present an intramolecular N-H···O=C contact (Tab. 1, Fig. 2). The crystal packing can be described as H-bonded interlocked Z-shaped ribbons caused by the presence of additional short contacts C-H···Br (Fig. 3).

Refinement
All the hydrogens were discernible in the difference electron density map. However, all the hydrogens were situated into idealized positions and refined riding on their parent C or N atoms, with N-H = 0.88 Å, U(H) = 1.2U eq (C), C-H = 0.95Å (for aryl H), C-H = 0.99 Å for methylene and C-H = 1.00 Å for methine, U(H) = 1.2U eq (C/N) for the amine, methylene and methine H atoms, respectively. Fig. 1. View of the title molecule with the displacement ellipsoids shown on 50% probability level. The H atoms are shown with arbitrary radius.  Br1c: x, -1+y, z; for Br1d: 1-x, -1/2+y, 3/2-z; for another isothiuronium fragment: x, 1+y, z.

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 calculat-supplementary materials sup-4 ing 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Geometric parameters (Å, °)