Crystal structure and Hirshfeld surface analysis of (E)-1-[(4,7-dimethylquinolin-2-yl)methylidene]semicarbazide dihydrate

The semicarbazone derivative molecule is almost planar. In the crystal, the molecules are linked by O—H⋯O, N—H⋯O and O—H⋯N hydrogen bonds.


Chemical context
Semicarbazones are important intermediates in organic synthesis, mainly for obtaining heterocyclic rings such as oxadiazoles and pyrazolidones (Arfan & Rukiah, 2015). Furthermore, they are used for the isolation, purification and characterization of aldehydes and ketones as well as for the protection of carbonyl groups. They possess a wide range of bioactivities and pharmacological applications (Jadon et al., 2011). The chemistry of semicarbazones is interesting because of their special role in biological applications, exhibiting antiproliferative, anti-tumoral, anticonvulsant, anti-trypanosomal, herbicidal and biocidal activities (Arfan & Rukiah, 2015). Beside these, a number of semicarbazones have also been reported to possess antifungal, antibacterial and antitubercular activities (Jadon et al., 2011). Semicarbazones are commonly used as ligands in coordination chemistry and are biologically active compounds. Their complexation with different metals increases the bioactivity of these molecules (Nasrullah et al., 2013, Afrasiabi et al., 2005. Semicarbazones exist predominantly in the amido form in the solid state whereas due to the interactions of the solvent molecules they can exhibit a amido-iminol tautomerism in solution state (Casas et al., 2000).

Supramolecular features
The crystal packing of the title compound features four intermolecular (O-HÁ Á ÁO, N-HÁ Á ÁO and O-HÁ Á ÁN) hydrogen bonds (Table 1 and Fig. 2) as well as those already mentioned, forming a two-dimensional network parallel to (101). All three O atoms of the compound are involved in hydrogen bonds.

Hirshfeld surface analysis
Hirshfeld surface was used to investigate and quantify the intermolecular interactions in the title structure (Crystal-CrystalExplorer; Turner et al., 2017). The Hirshfeld surfaces were plotted using a standard (high) surface resolution with the three-dimensional d norm surfaces mapped over a fixed colour scale of À0.578 (red) to 1.362 (blue) a.u. The red spots on the surfaces indicate the intermolecular contacts involved in the hydrogen bonds (Sen et al., 2018;Kansiz et al., 2018;Gü mü ş et al., 2018). Those in Figs. 3 and 4 correspond to the near-type HÁ Á ÁO and HÁ Á ÁN contacts resulting from O-HÁ Á ÁO, N-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds (Table 1). Fig. 5 shows the two-dimensional fingerprint of the sum of the contacts contributing to the Hirshfeld surface represented in normal mode. Fig. 6a (HÁ Á ÁH) shows the two-dimensional fingerprint of the (d i , d e ) points associated with hydrogen atoms. It is characterized by an end point that points to the origin and corresponds to d i = d e = 1.2 Å , which indicates the presence of the HÁ Á ÁH contacts in this study (55.4%).  Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 5 2 ; y À 1 2 ; Àz þ 3 2 ; (ii) Àx þ 2; Ày þ 1; Àz þ 1.

Figure 2
A view of the crystal packing of the title compound. Dashed lines denote hydrogen bonds (Table 1).

Figure 1
The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 20% probability level.
outside the surface and has two symmetrical points at the top, bottom left and right, d e + d i = 1.9 Å . These data are char-acteristic of O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds. Fig. 6c shows the contacts (CÁ Á ÁH/HÁ Á ÁC = 11.7%) between the carbon atoms inside the surface and the hydrogen atoms outside the surface of Hirshfeld and vice versa. There are two symmetrical wings on the left and right sides. In Fig. 6d Hirshfeld surfaces mapped over d norm to visualize the intermolecular interactions.

Figure 5
The overall fingerprint plot for the title compound.  The Hirshfeld surfaces of the title compound mapped over d norm , d i and d e .

Synthesis and crystallization
The title compound was synthesised following a reported procedure by (Aydemir & Kaban, 2018). A hot ethanolic solution (5 mL) of of semicarbazide hydrochloride (1 mmol) and (0.1 mol) of sodium acetate trihidrate (1.5 mmol) in 2 mL water was slowly added to a solution of 2,7-dimethylquinoline-2-carboxaldehyde (1.0 mmol) in 10 mL of hot ethanol. The mixture was refluxed on a steam bath for 2 h until the colour changed. On completion of the reaction (monitored by TLC) the mixture was allowed to cool to room temperature. The separated solid was filtered and washed with cold water, ethanol and diethyl ether and then single crystals suitable for X-ray diffraction analysis were grown by slow evaporation of a saturated solution of the resultant compound in acetonitrile; colourless prismatic crystals were obtained in 83% yield, m.p. 503.5 K (decaying).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were geometrically positioned with C-H distances of 0.93-0.96 Å . and refined as riding, with U iso (H) = 1.2U eq (C). N-bound H atoms were located in difference-Fourier maps and refined isotropically. The water H atoms were located in a difference-Fourier map and refined isotropically subject to a restraint of O-H = 0.85AE2 Å .   (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2009). 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.