m-Xylylenediaminium dinitrate

The asymmetric unit of the title salt, C8H14N2 2+·2NO3 −, contains two independent dications and four independent nitrate anions. The crystal structure consists of discrete nitrate ions, three of which stack in layers parallel to (001) at z = 0 and 0.5. These layers are connected via m-xylylenediaminium dications. The fourth anion is sandwiched by the two independent organic cations in the asymmetric unit. In the crystal, the ions are connected by a large number of bifurcated and non-bifurcated N—H⋯O(O) hydrogen bonds, forming sheets parallel to (100). These sheets are connected by C—H⋯O hydrogen bonds, forming a three-dimensional network.


Experimental
Crystal data

Synthesis and crystallization
An aqueous solution containing 4 mmol of HNO 3 in 10 ml of water was added to 2 mmol of m-xylylenediamine in 10 ml of water. The obtained solution was stirred for 1 h and then left to stand at room temperature. Colorless single crystals of the title compound were obtained after one week.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms bonded to C and N atoms were treated as riding with C-H = 0.99 Å (methylene) or 0.95 Å (aromatic CH), N-H = 0.91 Å (NH 3 ), and with U iso (H) = 1.2U eq (C) and U iso (H) = 1.5U eq (N).

Results and discussion
As a part of our study of crystal packing containing the nitrate anion (Marouani et al., 2012;Gatfaoui et al., 2013Gatfaoui et al., , 2014Kefi et al., 2013), we report here the preparation and the structural investigation of a new organic nitrate, (C 8 H 14 N 2 )·(NO 3 ) 2 (I). The asymmetric unit of (I) is composed of two m-xylylenediaminium dications and four nitrate anions (Fig. 1). The structure of the compound consists of discrete nitrate ions stacked in layers parallel to the (001) plane at z = 0 and 1/2, for N6/O4/O5/O6, N7/O7/O8/O9, N8/O10/O11/O12 and at z = 0.25 and 0.75 for N5/O1/O2/O3, separated by organic cations. Each organic entity is connected to different nitrate layers at z = 0 and 1/2. At the same time, the N5O 3 nitrate groups ensure the cohesion between the organic groups ( Fig. 2). The structural cohesion is established by a three-dimensional network of N-H···O and weak C-H···O hydrogen bonds.
Interatomic bond lengths and angles of the nitrate anions spread respectively within the ranges 1.2314 (19)-1.2719 (17) Å and 118.69 (15)-121.48 (13)°. These geometrical features have also been noticed in other related crystal structures (Gatfaoui et al., 2013(Gatfaoui et al., , 2014. In this crystal arrangement two independent m-xylylediaminium cations are present. Both ammonium groups in each cation adopt a cis conformation with respect to the benzene ring. The trans conformation has been observed in C 8 H 14 N 2 2+ ·2Cl - (Cheng & Li, 2008). Thus, the cation conformation is modified when substituting nitrate anions by chlorides. Examination of the organic cations shows that the bond distances and angles show no significant differences from those obtained in other compounds involving the same organic groups (Cheng & Li, 2008). The aromatic rings are planar with an average deviation of 0.0022 Å and form a dihedral angle of 3.85° in the asymmetric unit. The inter-planar distance between nearby benzene rings in the crystal structure is in the vicinity of 4.59 Å, which is much longer than 3.80 Å, value required for the formation of π-π interactions (Janiak, 2000).