m-Xylylenediaminium sulfate: crystal structure and Hirshfeld surface analysis

The crystal structure of the title salt consists of infinite (100) sheets of alternating organic and inorganic entities The m-xylylenediaminium cations are linked to the sulfate anions by N—H⋯O and asymmetric bifurcated N—H⋯(O,O) hydrogen bonds, generating a three-dimensional network. The Hirshfeld surface analysis and the two-dimensional fingerprint maps indicate that the packing is dominated by H⋯O/O⋯H and H⋯H contacts.


Chemical context
m-Xylylenediaminum compounds have been intensively investigated due to their good antimicrobial activity against various antibacterial and antifungal species (Murugesan et al., 2015). Sequestration of carbon dioxide by m-xylylenediamine with formation of a crystalline adduct has been reported (Lee et al., 2013). In addition, polyamides of m-xylylenediamine possess dielectric properties (Murata et al., 1999). In this work, as part of our studies in this area, we report the synthesis, the structural investigation and the Hirshfeld surface analysis of a new organic sulfate salt, (C 8 H 14 N 2 )SO 4 , (I).

Structural commentary
The asymmetric unit of (I) comprises one m-xylylenediaminium cation and one sulfate anion (Fig. 1). Both ammonium groups in the m-xylylenediaminium cation adopt a trans conformation with respect to the benzene ring. The same conformation has been observed in C 8 H 14 N 2 2+ Á2Cl À (Cheng & Li, 2008), but in C 8 H 14 N 2 2+ Á2NO 3 À (Gatfaoui et al., 2014) the cis conformation occurs. Thus, the cation conformation is modified when substituting sulfate or chloride anions by nitrates. Examination of the organic cations shows that the bond distances and angles show no significant differences from those in other compounds involving the same organic groups (Cheng & Li, 2008;Gatfaoui et al., 2014). The aromatic ring of ISSN 2056-9890 the cation is essentially planar with an r.m.s. deviation of 0.0014 Å .
In the sulfate anion, the S-O bond lengths range from 1.4673 (12) to 1.4895 (11) Å . Their similar values confirm the absence of a proton in this anion. It is worth noting that the S-O4 distance is the longest because O4 accepts three hydrogen bonds, one of which is considered to be strong (Blessing, 1986;Brown, 1976 (Marouani et al., 2011a,b). The calculated average values of the distortion indices (Baur, 1974) corresponding to the different angles and distances in the SO 4 tetrahedron [DI(SO) = 0.006, DI(OSO) = 0.008, and DI(OO) = 0.003] show a slight distortion of the OSO angles if compared to the SO and OO distances. Hence, the SO 4 group can be considered as a rigid regular arrangement of oxygen atoms, with the sulfur atom slightly displaced from the centre of gravity.

Supramolecular features
The packing of the title salt is dominated by hydrogen bonding, as detailed in Table 1. Ten distinct hydrogen bonds of types N-HÁ Á ÁO and C-HÁ Á ÁO involve all of the oxygen atoms of the sulfate anions as acceptors, However, only two of the N-HÁ Á ÁO hydrogen bonds are considered as strong according to the Blessing and Brown criteria (Blessing, 1986;Brown, 1976).

Figure 2
The 12-membered ring motif R 4 4 (12) in (I). C atoms have been omitted for clarity.

Figure 3
Projection of (I) along the b axis. H atoms not involved in hydrogen bonding have been omitted.

Figure 1
A view of (I), with displacement ellipsoids drawn at the 30% probability level. H atoms are represented as small spheres of arbitrary radii. Hydrogen bonds are shown as dotted lines.
The inter-planar distance between nearby benzene rings in the crystal structure is in the vicinity of 4.63 Å , which is much longer than 3.80 Å , value required for the formation ofinteractions (Janiak, 2000).

Hirshfeld analysis
The three-dimensional Hirshfeld surfaces and two-dimensional fingerprint plots of (I) were prepared using Crystal-Explorer (Wolff et al., 2012) and are shown in Fig. 4 and Fig. 5, respectively.
The OÁ Á ÁH/HÁ Á ÁO contacts, which are attributed to N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen-bonding interactions, appear as two sharp symmetric spikes in the two-dimensional fingerprint maps with a prominent long spike at d e + d i = 1.8 Å . They have the most significant contribution to the total Hirshfeld surfaces (51.4%). The HÁ Á ÁH contacts appear in the middle of the scattered points in the two-dimensional fingerprint maps with a single broad peak at d e = d i = 1 Å and a percentage contribution of 32.1%. The 15.9% contribution from the CÁ Á ÁH/HÁ Á ÁC contacts to the Hirshfeld surface, generally slightly favoured in a sample of CH aromatic molecules, results in a symmetric pair of wings, Fig. 5c. The OÁ Á ÁO contacts, which represent only 0.2% of the Hirshfeld surface, Fig. 5d, are extremely impoverished in the crystal (enrichment ratio E OO = 0.03) (Jelsch et al. 2014), as the oxygen atoms bound to sulfur and the SO 4 group as a whole are electronegative, therefore the OÁ Á ÁO contacts are electrostatically repulsive.

Synthesis and crystallization
Equimolar solutions of m-xylylenediamine dissolved in methanol and aqueous sulfuric acid were mixed together and stirred for about 1 h. Crystals of (I) were formed as the solvent evaporated over a few days at room temperature: these were     filtered off, dried and repeatedly recrystallized as colourless prisms to enhance the purity of the product.

[1,3-Phenylenebis(methylene)]bis(azanium) sulfate
Crystal data 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.