Crystal structure and Hirshfeld surface analysis of 4-bromoanilinium nitrate

In the crystal, π-π stacking interactions and strong N—H⋯O and C—H⋯O hydrogen bonds link the cations and anions into layers parallel to the bc plane. The O⋯H/H⋯O interactions between the cation and anion are the major factor determining the crystal packing.


Chemical context
In recent years, halogenated anilines and their derivatives have been studied extensively for applications as anticorrosives, antibacterials and in non-linear optical systems (Glidewell et al., 2005;Vivek et al., 2014). The simplest halogenated aniline readily forms metal/non-metal complexes (Hartmann et al., 1990). Strong hydrogen bonding, noncovalent bonding andstacking interactions are prominent in the supramolecular arrangements of this molecule. Here, we report the crystal structure of 4-bromoanilinium nitrate, a salt complex whose structure is closely related to its 4-iodo analogue regarding the hydrogen-bond networks andinteractions  although having significantly different unit-cell parameters.

Structural commentary
The asymmetric unit consists of two 4-bromoanilinium cations and two nitrate anions which are associated through N1-H10Á Á ÁO4 ii , N2-H13Á Á ÁO3 iv and a bifurcated N1-H9Á Á ÁO2 i / N1-H9Á Á ÁO3 i hydrogen bonds (Fig. 1). This motif generates a van der Waals contact (O3Á Á ÁO6) of 2.980 (4) Å between the ISSN 2056-9890 two nitrate ions. The phenyl rings in the independent cations extend in the same direction from the pair of anions with a dihedral angle of only 4.8 (2) between their mean planes and participate in astacking interaction with a centroidÁ Á Ácentroid distance of 3.932 (2) Å . Meanwhile, one cation is rotated with respect to the other so that the Br1-C2Á Á ÁC10-Br2 torsion angle is 50.4 (su?) .

Supramolecular features
In the crystal, the anions are arranged in coarsely corrugated layers parallel to the bc plane with the hydrogen-bonded cations protruding from each face in an alternating fashion (Fig. 2). The cations containing Br1 are perpendicular to the layers and make close Br1Á Á ÁO5 contacts of 3.229 (5) Å (0.14 Å less than the sum of the van der Waals radii) with nitrate ions in adjacent layers (Fig. 2

Hirshfeld surface analysis
The intermolecular interactions were investigated quantitatively and visualized with Crystal Explorer 3.1 (Wolff et al., 2012;Spackman et al., 2009) The asymmetric unit with labelling scheme and 50% probability ellipsoids. N-HÁ Á ÁO hydrogen bonds and -stacking interactions are shown, respectively, by blue and orange dashed lines.

Figure 3
Hirshfeld surface plotted over d norm .

Figure 4
Curvedness surface of the title compound showing thestacking.

Synthesis and crystallization
The title salt was synthesized by dissolving analytical grade 4bromoaniline and nitric acid in a 1:1 stoichiometric ratio in methanol. The solution was stirred continuously for 2 h. Slow evaporation of this solution at room temperature yielded transparent colourless single crystals of the product.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were positioned geometrically and refined using a riding model: C-H = 0.93 Å with U iso (H) = 1.2U eq (C) and N-H = 0.86 Å with U iso (H) = 1.2U eq (N). Reflection (100) was obscured by the beam stop and was omitted during the final refinement cycle.

Funding information
RA gratefully acknowledges Periyar University for providing financial support under the University Research Fellowship (URF) scheme.