Crystal structure, DFT and Hirshfeld surface analysis of (E)-N′-[(1-chloro-3,4-dihydronaphthalen-2-yl)methylidene]benzohydrazide monohydrate

In the title compound, C18H15ClN2O·H2O, the dihedral angle between the mean plane of the dihydronaphthalene ring system and the phenyl ring is 17.1 (2)°. In the crystal, molecules are linked by O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds.


Chemical context
Benzohydrazides are versatile compounds in medicinal chemistry that are used for the development of new drugs (Veeramanikandan et al., 2015). Benzohydrazide derivatives are potent inhibitors of prostate cancer (Arjun et al., 2019) and show anti-inflammatory (Todeschini et al., 1998), anti-malarial (Melnyk et al., 2006), entamoeba histolyica (Inam et al., 2016) and anti-tuberculosis (Bedia et al., 2006) activities. Herein we describe the molecular and crystal structures of the title compound, which can act as a potential multidrug ligand for various biological activities. The molecular packing was further studied with Hirshfeld surface analysis and PIXEL methods (Sowmya et al., 2018).

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The benzohydrazide molecule adopts an E configuration with respect to the C8 N2 bond. The cyclohexene ring (C9-C12/C17/C18) adopts nearly a half-chair conformation, as indicated by the total puckering amplitude Q T of 0.431 (3) Å and spherical polar angle = 115.6 (3) with ' = 264.4 (4) ; atom C10 shows a maximum deviation of 0.282 (4) Å from the mean plane. The phenyl ring (C1-C6) and the mean plane of the dihydronaphthalene ring system (C9-C18) are inclined to each other by 17.1 (2) . The central hydrazine fragment (C8/ N2/N6/C7/O1) is almost planar, making dihedral angles of 11.0 (2) and 8.49 (18) , respectively, with the phenyl ring and the mean plane of the dihydronaphthalene ring system.

Supramolecular features and Hirshfeld surface analysis
In the crystal, the water molecule forms five hydrogen bonds with three benzohydrazide molecules. The benzohydrazide molecules are stacked in a column along the b-axis direction through O-HÁ Á ÁO hydrogen bonds (O2-H2AÁ Á ÁO1 i and O2-H2BÁ Á ÁO1; symmetry code as in Table 1) between the H atoms of the water molecule and the carbonyl O atoms of two adjacent benzohydrazide molecules (Fig. 2). The water molecule also acts as a hydrogen-bond acceptor from other benzohydrazide molecules: N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds (N6-H6Á Á ÁO2 ii , C1-H1Á Á ÁO2 ii and C8-H8Á Á ÁO2 ii ; Table 1) link the molecules, forming a layer parallel to the bc plane.

Interaction energies and theoretical calculations
The various intermolecular interaction energies of the title crystal were calculated using the PIXEL-CLP module (Gavezzotti, 2003 Symmetry codes: (i) x; y þ 1; z; (ii) Àx þ 1; Ày; z À 1 2 .   The molecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The O-HÁ Á ÁO hydrogen bond is indicated by a dashed line.

Figure 4
Two-dimensional fingerprint plots for the title compound with the percentage contribution of the intermolecular contacts. The d i and d e values are the closest internal and external distances (Å ) from given points on the Hirshfeld surface.
is found to be À67.2 kJ mol À1 with the energy partitioned into Coulombic, polarization, dispersion and repulsion energy components of À68.4, À30.7, À95.3 and 128.1 kJ mol À1 , respectively. The important molecular pairs (motifs A-F) and their interaction energies are shown in Fig. 5, and the partitioned intermolecular energies along with the above interactions are given in Table 2. The N-HÁ Á ÁO interaction energy in motif F (À32.8 kJ mol À1 ) is strongest followed by the O-HÁ Á ÁO interactions in motifs A and E (À27.1 and À23.9 kJ mol À1 , respectively), and the C-HÁ Á ÁO interaction in motif B (À16 kJ mol À1 ). Density functional theory (DFT) calculations using the B3LYP (Becke, 1993) method at the 6-31++G(d,p) level were performed using GAUSSIAN09 (Frisch et al., 2009). The DFToptimized structure of the title compound is found to be in good agreement with the experimental geometry. Frontier molecular orbitals are plotted to specify the distribution of electronic densities (Fig. 6); the HOMO-LUMO gap of 3.6349 eV indicates that the nature of molecule is soft. The quantum-chemical parameters, such as hardness (), softness (), chemical potential (), electrophilicity (!) and electronegativity (), were also calculated (Table 3), using the HOMO and LUMO energies. The electrophilicity index (!) of 4.3148 eV, which measures the energy lowering due to the electron flow between the donor and acceptor, also supports the soft nature of the title compound. The lower chemical potential () of À3.9602 eV signifies the lesser resistance towards the deformation or polarization of the electron cloud of the atoms or molecule under a small perturbation of chemical reaction. The frontier molecular orbitals, highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO), calculated for the title compound. Table 2 List of intermolecular interaction energies (kJ mol À1 ) in the crystal of the title compound.

Synthesis and crystallization
Phosphoryl chloride (POCl 3 ) (0.171mol) was slowly added to dry dimethyl formamide at 273 K, and then 3,4-dihydronaphthalen-1(2H)-one (0.174 mol) was added. The mixture was stirred at 353 K for 1.5 h. The reaction mixture was then poured into aqueous sodium acetate (3 mol l À1 ) and the product was extracted with ethyl acetate. Evaporating the ethyl acetate gave an oil, which on cooling solidified to yield 1-chloro-3,4-dihydronaphthalene-2-carbaldehyde. The title compound was prepared by refluxing 1-chloro-3,4-dihydronaphthalene-2-carbaldehyde (0.01 mol) with benzohydrazide (0.01 mol) in ethanol (5 ml) and few drops of acetic acid for 8 h. The reaction mixture was then cooled to room temperature, excess ethanol was removed under vacuum and the residue was quenched with ice. The precipitate was filtered, dried and crystallized from ethanol. The completion of the reaction was monitored by thin layer chromatography. Single crystals suitable for X-ray diffraction study were grown from an N,N-dimethylformamide solution by slow evaporation.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. The N-bound H atom (H6) and water H atoms (H2A and H2B) were located in a difference-Fourier map and refined isotropically. All C-bound H atoms were placed in idealized positions (C-H = 0.93 or 0.97 Å ) and treated as riding with U iso (H) = 1.2U eq (C).  Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SIR2011 (Burla et al., 2012); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008); software used to prepare material for publication: WinGX (Farrugia, 2012), PLATON (Spek, 2009) and publCIF (Westrip, 2010). 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.