A triclinic polymorph of 3-nitroanilinium chloride

The asymmetric unit of the title compound, C6H7N2O2 +·Cl−, contains two independent ion pairs. A monoclinic form of the title compound with only one ion pair in the asymmetric unit has been reported previously [Ploug-Sørensen & Andersen (1986). Acta Cryst. C42, 1813–1815]. In the crystal of the title compound, the components are linked into layers parallel to (001) by intermolecular N—H⋯Cl hydrogen bonds, with alternating hydrophilic and hydrophobic regions.

The asymmetric unit of the title compound, C 6 H 7 N 2 O 2 + ÁCl À , contains two independent ion pairs. A monoclinic form of the title compound with only one ion pair in the asymmetric unit has been reported previously [Ploug-Sørensen & Andersen (1986). Acta Cryst. C42, [1813][1814][1815]. In the crystal of the title compound, the components are linked into layers parallel to (001) by intermolecular N-HÁ Á ÁCl hydrogen bonds, with alternating hydrophilic and hydrophobic regions.
Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXTL/PC (Sheldrick, 2008 molecules including most of pharmaceutical compounds are prone to polymorphic formation in the solid state. Variations in crystallization environment (e.g., solvent, temperature, using as additives and concentration), can cause the same molecules to pack differently and form different crystal lattices or polymorphs (Davey, 2003). As a result, the physical, chemical and mechanical properties of crystals can be dramatically affected (Li et al., 2001). It is now widely appreciated that the occurrence of polymorphism in molecular crystalline solids impacts on the production of fine chemical products such as pharmaceuticals, pigments and photographic couplers (Rodríguez-Spong et al., 2004).
The title compound, (I), crystallizes with two crystallographically independent 3-nitroanilinium cations and two chloride anions in the asymmetric unit of the triclic unit cell, with the spacegroup P1. A monoclinic form with space group P2 1 /c has been previously reported by Ploug-Sørensen & Andersen (1986). In the title compound the nitro groups of the cations are twisted from the plane of the aromatic rings by 0.32 (3) and 7.1 (3)°. The protonation on the N atom of the cations are confirmed from the elongated C-N bond distances.
The crystal packing, is stabilized through intermolecular N-H···Cl interactions, as shown in Fig. 2 and hydrogen bond parameters are listed in Table 1. All ammonium H atoms of the cations are involved in the hydrogen bonds with the chloride anions. The cations and anions are connected to form R 4 2 (8) ring motifs (Etter et al., 1990). Overall, the components are linked into two-dimensional layers parallel to (001) by the intermolecular N-H···Cl hydrogen bonds. This type of aggregation forms alternating hydrophilic and hydrophobic regions.

Experimental
The title compound, (I), was crystallized from an aqueous mixture of 3-nitroaniline and hydrochloric acid in the stochiometric ratio of 1:1 at room temperature, by the technique of slow evaporation.

Refinement
The H atoms, which participate in hydrogen bonds, were located in difference Fourier maps and then refined isotropically    (4)