Synthesis and crystal structure of (E)-2-({2-[azaniumylidene(methylsulfanyl)methyl]hydrazinylidene}methyl)benzene-1,4-diol hydrogen sulfate

The title molecular salt was obtained through the protonation of the azomethine N atom in a sulfuric acid medium. The crystal comprises two entities, a thiosemicarbazide cation and a hydrogen sulfate anion. The cation is essentially planar and is further stabilized by a strong intramolecular O—H⋯N hydrogen bond.


Chemical context
Thiosemicarbazones and their complexes are well known for their pharmacological properties, as antimicrobial (Plech et al., 2011;Pandeya et al., 1999;Kü çü kgü zel et al., 2006), antiinflammatory (Palaska et al., 2002) and antiumoural (de Oliveira et al., 2015) agents. Complexes of thiosemicarbazones are studied in the literature as drug candidates, biomarkers and biocatalysts (Hayne et al., 2014;Lim et al., 2010). It is believed that the biological activity of these compounds has a strong relationship with the nature of the aldehydes and ketones from which those thiosemicarbazones were obtained (Teoh et al., 1999), and also on the substituents attached at the + NH 2 N atom (Beraldo & Gambino, 2004). An interesting attribute of thiosemicarbazones is their ability to exhibit thione-thiol tautomerism and they can also exist as E and Z isomers. Thiosemicarbazones have an excellent capacity to complex transition metals, acting as chelating agents; this process usually takes place via dissociation of the acidic proton (Pal et al., 2002). The crystal structure of the title molecular salt was determined in order to investigate its biological and catalytic activities.

Structural commentary
The molecular structure of the title molecular salt is illustrated in Fig. 1. It comprises two entities, i.e. a thiosemicarbazone cation and a hydrogen sulfate anion. The cation is essentially planar and shows an E conformation with regard to the C6-N5 bond, the maximum deviation from the mean plane through the 15 non-H atoms being 0.1 (2) Å for atom C6. This planarity is due to electron delocalization along the cation backbone, which is further stabilized by an intramolecular O13-H13Á Á ÁN5 hydrogen bond (Zhu et al., 2004). The bond lengths and angles resemble those observed for similar thiosemicarbazone derivatives (Gangadharan et al., 2015;Joseph et al., 2004;Nehar et al., 2016;Houari et al., 2013). The anion (hydrogen sulfate) is disordered, split over two sets of siteswith relative occupancies of 0.501 (6) and 0.499 (6), and labelled with A and B suffixes.

Supramolecular features
In the crystal, the three-dimensional structure is established through an extensive network of O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds. Also within this network exists a weak C-HÁ Á ÁO intermolecular hydrogen bond (Table 1 and

Figure 1
The molecular structure of the title molecular salt, showing the labelling and with displacement ellipsoids drawn at the 50% probability level. The disordered hydrogen sulfate anion is shown.

Figure 2
Projection along the a axis of the crystal packing of the title molecular salt. Hydrogen bonds are shown as dashed lines.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The hydrogen sulfate anion is disordered and had to be modelled as two conformations A and B, with relative occupancies of 0.501 (6) and 0.499 (6), respectively. H atoms were located in difference Fourier maps, but were subsequently included in calculated positions and treated as riding on their parent atoms with constrained thermal parameters: U iso (H) = 1.5U eq (C) and C-H = 0.98 Å for methyl H atoms, and U iso (H) = 1.2U eq (C,N) and C-H = 0.95 Å or N-H = 0.88 Å otherwise.

(E)-2-({2-[Azaniumylidene(methylsulfanyl)methyl]hydrazinylidene}\ methyl)benzene-1,4-diol 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.