Synthesis and crystal structure of ((E)-{2-[(E)-(4-hydroxynaphthalen-1-yl)methylidene]hydrazin-1-yl}(methylsulfanyl)methylidene)azanium hydrogen sulfate monohydrate

In the title molecular salt, C13H14N3S+·HSO4 −·H2O, the protonation of the azomethine N atom in sulfuric acid medium involves the formation of a bisulfate anion. The molecular structure of the cation is obtained from the thiol tautomer of thiosemicarbazone wherein the naphthalene moiety and the conjugation of the bonds contribute to the planarity of the molecular skeleton.

In the title hydrated molecular salt, C 13 H 14 N 3 S + ÁHSO 4 À ÁH 2 O, the protonation of the azomethine N atom in sulfuric acid medium involves the formation of the bisulfate anion. The molecular structure of the cation is obtained from the thiol tautomer of thiosemicarbazone wherein the naphthalene moiety and the conjugation of the bonds contribute to the planarity of the molecular skeleton. In the crystal, the cation, anion and water molecule of crystallization are linked by a series of O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds, forming a threedimensional network. Within this network, there are also C-HÁ Á Á interactions present involving symmetry-related naphthalene rings.

Chemical context
Thiosemicarbazones and their metal complexes have been widely explored because of their pharmaceutical properties (Klayman et al., 1983). These compounds present a wide variety of biological activities, such as antitumoral, fungicidal and antiviral (Tarasconi et al., 2000), and bactericidal (Abram et al., 1998). The ability of thiosemicarbazone molecules to chelate with traces of metals in biological systems is believed to be a reason for their activity (Teoh et al., 1999). The nature of the aldehyde and ketone from which the thiosemicarbazone is obtained and the nature of the substituents attached at the + NH 2 N atom influence the biological activity (Beraldo & Gambinob, 2004). Thiosemicarbazones can exist as E and Z isomers and they exhibit thione-thiol tautomerism, as illustrated for the title compound in Fig. 1. Complexation usually Thiosemicarbazones can exist as E and Z isomers and they exhibit thione-thiol tautomerism. takes place via dissociation of the acidic proton, resulting in the formation of a five-membered chelate ring (Pal et al., 2002). The crystal structure of the title compound was determined in order to investigate the extent of electron delocalization, the ligand conformation and to explore its biological implications.

Structural commentary
The molecular structure of the title molecular salt is illustrated in Fig. 2. It is composed of three entities: a bisulfate anion, a thiosemicarbazone cation and a water molecule of crystallization. The cationic entity shows an E conformation with respect to the C12 N13 bond and is approximately planar, the maximum deviation from the mean plane through the 18 non-hydrogen atoms being 0.118 (2) Å for atom C12. This planarity is due to electron delocalization along the cationic entity backbone. Bond lengths and angles are close to those observed for similar (methylidene)hydrazinecarbothioamide derivatives (Gangadharan et al., 2015;Joseph et al., 2004;Houari et al., 2013.)

Supramolecular features
In the crystal, there is an extensive hydrogen-bonding network present. The cation, anion and water molecule of crystallization are linked by a series of O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network (Table 1 and Fig. 3). Within this network there are also C-HÁ Á Á interactions present involving symmetry-related naphthalene rings (Table 1) A view of the molecular structure of the title molecular salt, with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 3
A view along the a axis of the crystal packing of the title molecular salt. The hydrogen bonds are drawn as dashed lines (see Table 1) and the Cbound H atoms have been omitted for clarity. Table 1 Hydrogen-bond geometry (Å , ).

Database survey
A search of the Cambridge Structural Database (CSD, Version 5.37, update May 2016; Groom et al., 2016) for the S-methyl (methylidene)thiosemicarbazidium cation substructure gave two hits, viz. S-methyl-N 0 -(pyrrolyl-2 0 -methylene)isothiosemicarbazidium iodide monohydrate (JIHZUV; Bourosh et al., 1990) and 8-quinolinealdehyde S-methylthiosemicarbazone hydrochloride dihydrate (RUJXOK; Botoshansky et al., 2009). Only the coordinates for the latter structure were available. The cation in RUJXOK, is relatively planar and the bond lengths and angles in the S-methyl (methylidene)thiosemicarbazidium moiety are similar to those observed for the title compound.

Synthesis and crystallization
The synthesis of the title molecular salt is illustrated in Fig. 4. An equimolar amount of thiosemicarbazide 10 mmol (0.91 g) and 3-hydroxy-2-naphthaldehyde 10 mmol (1.72 g) were dissolved in a mixture of methanol and water (30 ml, 50%) and refluxed for 5 h in the presence of a catalytic amount of glacial sulfuric acid. Brown crystals suitable for X-ray diffraction analysis were obtained after slow evaporation of the solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The hydroxy H atom was located in a difference Fourier map and freely refined. The water and N-bound H atoms were located in difference Fourier maps and refined with distance restraints O-H = 0.84 (2)  The synthesis of the title molecular salt.    (5) 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.