Crystal structure and Hirshfeld surface analysis of rac-2-[2-(4-chlorophenyl)-3,4-dihydro-2H-1-benzopyran-4-ylidene]hydrazine-1-carbothioamide

The title compound, is a Schiff base derivative of a thiosemicarbazide with a flavanone. In the crystal, molecules are linked by two pairs of N—H⋯S hydrogen bonds, forming inversion dimers enclosing (8) ring motifs, which are linked to form ribbons propagating along the b-axis direction.

In the title compound, C 16 H 14 N 3 OSCl, a Schiff base derivative of a thiosemicarbazide with a flavanone, the 4-chlorophenyl ring is inclined to the benzene ring of the chromane ring system by 30.72 (12) . The pyran ring has an envelope conformation with the methine C atom as the flap. The mean plane of the thiourea unit is twisted with respect to the benzene ring of the chromanone ring system, subtending a dihedral angle of 19.78 (19) . In the crystal, molecules are linked by two pairs of N-HÁ Á ÁS hydrogen bonds, forming inversion dimers enclosing R 2 2 (8) ring motifs, which are linked to form ribbons propagating along the b-axis direction. The intermolecular contacts in the crystal have been analysed using Hirshfeld surface analysis.

Chemical context
Flavanones, a subclass of flavonoids, are widely recognized for their nutraceutical values (Testai & Calderone, 2017). Flavanones are also known for their potential bioactivities against cancer (Bauvois et al., 2003). Thiosemicarbazides are a class of versatile ligands exhibiting important physicochemical properties due to their -delocalization and flexibility of coordination modes. Therefore, a combination of flavanones and thiosemicarbazides may lead to compounds having synergistic properties of both classes of compounds. Schiff base derivatives of thiosemicarbazides have been studied for their biological and pharmacological properties (Bai et al., 2017). However, Schiff base derivatives of flavanones with thiosemicarbazides have not been explored extensively (Brodowska et al., 2016;Bargujar et al., 2018). In particular, structurally characterized flavanone-thiosemicarbazone Schiff bases are rare in the literature. The presence of NH and S moieties in such compounds opens up the possibility of studying the role of the comparatively less explored class of N-HÁ Á ÁS interactions in building supramolecular architectures. This is of interest as hydrogen bonding to sulfur is known to play an important role in biological systems (Andersen et al., 2014;Walters et al., 2005). Considering the above, we have synthesized the title compound through a Schiff base condensation reaction, and report herein on its crystal structure and the Hirshfeld surface analysis.

Structural commentary
The molecular structure of the title compound is illustrated in Fig. 1. The 4-chlorophenyl ring (C11-C16) is inclined to the benzene ring (C5-C10) of the chromanone ring system by 30.72 (12) . The pyran ring (O1/C2-C5/C10) has an envelope conformation with atom C2 as the flap, being displaced by 0.655 (2) Å from the mean plane through the other five atoms of the ring. The mean plane of the thiourea unit (N2/C17/S1/ N3) is twisted with respect to benzene ring (C5-C10) of the chromane ring system, forming a dihedral angle of 19.78 (19) .

Supramolecular features
A strong hydrogen bond often involves highly electronegative second row elements such as N, O and F. However, the less electronegative third row elements (P, S and Cl) are also known to take part in hydrogen-bonding interactions. In the crystal of the title compound, molecules are linked by two pairs of N-HÁ Á ÁS hydrogen bonds, forming inversion dimers enclosing R 2 2 (8) ring motifs, which are linked to form ribbons propagating along the b-axis direction (Table 1 and Fig. 2). In the crystal, there are no other significant short intermolecular interactions present.

Hirshfeld surface analysis and two-dimensional fingerprint plots for the title compound
The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) and the associated two-dimensional fingerprint plots (McKinnon et al., 2007) were performed with Crystal-Explorer17 (Turner et al., 2017). A recent article by Tiekink and collaborators (Tan et al., 2019) 'outlines the various procedures and what can be learned by using CrystalExplorer'.
The Hirshfeld surface of the title compound mapped over d norm is given in Fig. 3a. The red spots indicate specific points of contact in the crystal. The Hirshfeld surface mapped over the shape-index is given in Fig. 3b, showing red spots and blue regions indicative of possible CÁ Á ÁH/HÁ Á ÁC (i.e. C-HÁ Á Á) contacts. The Hirshfeld surface mapped over the curvedness is given in Fig. 3c. Here the region around the chromane ring system is fairly flat, indicative of possibleinteractions. However, these interactions must be extremely weak as analysis of the structure using PLATON (Spek, 2009) Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view normal to plane (101) of the crystal packing of the title compound. The N-HÁ Á ÁS hydrogen bonds are shown as dashed lines (Table 1). For clarity, C-bound H atoms have been omitted.

Figure 1
A view of the molecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The orientation of the fiigure means that one of the two H atoms on C3 is not shown.
indicate the presence of any significant C-HÁ Á Á or offsetinteractions in the crystal. The full two-dimensional fingerprint plot for the title compound is given in Fig. 4a. The principal intermolecular interactions ( Fig. 4b-4f) are delineated into HÁ Á ÁH (38.9%), CÁ Á ÁH/HÁ Á ÁC (20.3%), SÁ Á ÁH/HÁ Á ÁS (13.1%), ClÁ Á ÁH/HÁ Á ÁCl (12.0%) and NÁ Á ÁH/HÁ Á ÁN (3.0%) contacts. Note that only for the HÁ Á ÁH, CÁ Á ÁH/HÁ Á ÁC and SÁ Á ÁH/HÁ Á ÁS contacts is d e + d i (where d e and d i are the distances from a given point on the surface to the nearest atom outside and inside, respectively), less than the sum of the van der Waals radii of the individual atoms.  Nie et al., 2006). Here, the pyran ring has an envelope conformation and the 4-fluorophenyl ring is inclined to the benzene ring of the chromane ring system by 66.57 (11) . In the title compound, the pyran ring also has an envelope conformation and the 4-chloropheny ring is inclined to the benzene ring of the chromane ring system by only 30.72 (12) .

Refinement
Crystal data, data collection and structure refinement details are summarized in