Crystal structure and Hirshfeld surface analysis of the hydrochloride salt of 8-{4-[(6-phenylpyridin-3-yl)methyl]piperazin-1-yl}-3,4-dihydroquinolin-2(1H)-one

The amine 8-{4-[(6-phenylpyridin-3-yl)methyl]piperazin-1-yl}-3,4-dihydroquinolin-2(1H)-one was crystallized as the hydrochloride salt 4-(2-oxo-1,2,3,4-tetrahydroquinolin-8-yl)-1-[(6-phenylpyridin-3-yl)methyl]piperazin-1-ium chloride. Its structure is compared to that of the salt 4-(2-oxo-1,2,3,4-tetrahydroquinolin-8-yl)-1-{[6-(4-fluorophenyl)pyridin-3-yl]methyl}piperazin-1-ium chloride monohydrate, a fluorinated analogue.

The crystal structure of the hydrochloride salt of II has been reported previously (Ullah & Altaf, 2014) and will be ISSN 2056-9890 compared here to that of the hydrochloride salt of compound I.

Structural commentary
Due to the difficulty of forming suitable crystals for X-ray diffraction analysis compounds I and II were converted to their hydrochloride salts by treatment with HCl in MeOH.
The organic cation of IÁHCl has a half-moon shape enclosing the chloride anion (Fig. 2). The molecular salt IIÁHCl crystallized as a monohydrate and here, while the cation also has a half-moon shape, it encloses the water molecule of crystallization (Ullah & Altaf, 2014;see Fig. S1 in the supporting information). The two cations differ essentially in the conformation of the biaryl group (rings B = N4/C15-C19 and C = C20-C25) and their orientation with respect to the aromatic ring (A = C4-C9) of the 3,4-dihydroquinolin-2(1H)one moiety. This is illustrated by the view of their structural overlap, shown in Fig. 3. In IÁHCl, pyridine ring B is inclined to phenyl ring C by 40.17 (8) while in IIÁHCl the equivalent dihedral angle is 10.06 (11) . In IÁHCl, ring A is inclined to rings B and C by 36.86 (8) and 14.16 (8) , respectively. These dihedral angles differ considerably from the dihedral angles in IIÁHCl, where ring A is inclined to rings B and C by 51.20 (9) and 41.40 (11) , respectively. In both compounds, the piperidine ring (N1/C1-C4/C9) has a screw-boat conformation with the torsion angle C1-C2-C3-C4 being À56.17 (18) in IÁHCl and À55.6 (2) in IIÁHCl. In both compounds, the piperazine ring (N2/N3/C10-C13) has a chair conformation.

Supramolecular features
In the crystal of IÁHCl, the organic cations are linked by a pair of N-HÁ Á ÁO hydrogen bonds, forming an inversion dimer enclosing an R 2 2 (8) ring motif ( Fig. 4 and Table 1). The Cl À anion is linked to the cation by an N-HÁ Á ÁCl hydrogen bond A view of the molecular structure of IÁHCl, with atom labelling. The displacement ellipsoids are drawn at the 50% probability level.

Figure 3
A view of the structural overlap of the cations of salts IÁHCl and IIÁHCl; r.m.s. deviation 0.125 Å (Mercury; Macrae et al., 2020). The structure of the IIÁHCl cation is given in red with the F atom in yellow (see also supplementary figure S1; Ullah & Altaf, 2014).

Figure 1
Chemical diagrams for adoprazine, bifeprunoc and compounds I and II.
( Fig. 4 and Table 1). The dimers are linked by a C-HÁ Á ÁO hydrogen bond, forming ribbons propagating along the a-axis direction. The ribbons are then linked via C-HÁ Á ÁCl hydrogen bonds to form layers lying parallel to the ab plane ( Fig. 5 and Table 1). There are C-HÁ Á Á(C4-C9) contacts present within the layers (Table 1), but there are no significant contacts present between the layers.
In the crystal of IIÁHCl (Ullah & Altaf, 2014;see Figs. S2 and S3, and Table S1 in the supporting information), the cations are linked by the water molecules of crystallization via N-HÁ Á ÁO w and O w -HÁ Á ÁO hydrogen bonds to form dimers with R 4 4 (12) ring motifs. The dimers are in turn linked by the Cl À anions, via O w -HÁ Á ÁClÁ Á ÁH-N hydrogen bonds, to form chains propagating along the b-axis direction. The chains are linked via C-HÁ Á ÁCl and C-HÁ Á ÁO hydrogen bonds, forming layers parallel to the ab plane.
In both cases, hydrogen-bonded layers are formed stacking along the c-axis direction and lying parallel to the ab plane. There are no significant directional inter-layer contacts present in either crystal structure.
The Hirshfeld surfaces are colour-mapped with the normalized contact distance, d norm , varying from red (distances shorter than the sum of the van der Waals radii) through white to blue (distances longer than the sum of the van der Waals radii). The Hirshfeld surfaces (HS) of IÁHCl and IIÁHCl mapped over d norm are given in Fig. 6. It is evident from Fig. 6a and 6b that there are important contacts present in the crystals of both compounds, the strong hydrogen bonds (Table 1 and Table S1) being indicated by the large red zones.
The percentage contributions of inter-atomic contacts to the HS for both compounds are compared in Table 2. The twodimensional fingerprint plots for the title salt, IÁHCl, and those for IIÁHCl, are compared in Figs. 7 and 8. They reveal, as expected, that the principal contributions to the overall HS surface involve HÁ Á ÁH contacts at 51.5 and 42.1%, respectively. The difference is attributed to the presence of FÁ Á ÁH/ HÁ Á ÁF contacts in the crystal of IIÁHCl, amounting to 7.5%. The second most important contribution to the HS is from the CÁ Á ÁH/HÁ Á ÁC contacts at 20.2 and 20.5%, for IÁHCl and A view of the hydrogen bonded dimer formation in the crystal of salt IÁHCl. Hydrogen bonds are shown as dashed lines (see Table 1). Table 1 Hydrogen-bond geometry (Å , ).

Figure 5
A view along the [111] direction of the crystal packing of salt IÁHCl.
Hydrogen bonds are shown as dashed lines (see Table 1).  The Hirshfeld surfaces of compounds IÁHCl and IIÁHCl, mapped over d norm in the colour ranges of À0.5847 to 1.5642 au. and À0.5555 to 1.5111 au., respectively.

Figure 8
The two-dimensional fingerprint plots for compounds (

Synthesis and crystallization
The synthesis of compounds I and II has been reported (Ullah, 2012; compounds 5c and 5d in that paper). Colourless platelike crystals of their hydrochloride salts were obtained by slow evaporation of solutions in dichloromethane and methanol; ratios (8:3) and (8.5:1.5), respectively.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The NH H atoms were located in a difference electron-density map and freely refined. The Cbound H atoms were included in calculated positions and refined as riding on the parent atom: C-H = 0.95-0.99 Å with U iso (H) = 1.2U eq (C).