2-[(2,4,6-Trimethylbenzene)sulfonyl]phthalazin-1(2H)-one: crystal structure, Hirshfeld surface analysis and computational study

The X-ray crystal structure of the title phthalazin-1-one derivative, C17H16N2O3S {systematic name: 2-[(2,4,6-trimethylbenzene)sulfonyl]-1,2-dihydrophthalazin-1-one}, features a tetrahedral sulfoxide-S atom, connected to phthalazin-1-one and mesityl residues. The dihedral angle [83.26 (4)°] between the organic substituents is consistent with the molecule having the shape of the letter V. In the crystal, phthalazinone-C6-C—H...O(sulfoxide) and π(phthalazinone-N2C4)–π(phthalazinone-C6) stacking [inter-centroid distance = 3.5474 (9) Å] contacts lead to a linear supramolecular tape along the a-axis direction; tapes assemble without directional interactions between them. The analysis of the calculated Hirshfeld surfaces confirm the importance of the C—H...O and π-stacking interactions but, also H...H and C—H...C contacts. The calculation of the interaction energies indicate the importance of dispersion terms with the greatest energies calculated for the C—H...O and π-stacking interactions.


Supramolecular features
The formation of a supramolecular tape sustained by phthalazinone-C 6 -C-HÁ Á ÁO(sulfoxide) contacts, Table 1, and (phthalazinone)-(phthalazinone) stacking is the main feature of the molecular packing in the crystal of (I), Fig. 2   The molecular structures of (I) showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level.
The -stacking occurs between centrosymmetrically related phthalazinone rings, i.e. between the N 2 C 4 and C 6 i rings with an inter-centroid distance = 3.5474 (9) Å , angle of inclination = 1.17 (7) for symmetry operation (i) 1 À x, 1 À y, 2 À z. As shown in Fig. 2(b), the tapes inter-digitate along the c-axis direction allowing for putative -stacking between mesityl rings but, the inter-centroid separation is long at 4.1963 (8) Å . The assemblies shown in Fig. 2(b) stack along the a-axis direction, again without directional interactions between them, Fig. 2(c).

Hirshfeld surface analysis
In order to probe the interactions between molecules of (I) in the crystal, the Hirshfeld surfaces and two-dimensional fingerprint plots were calculated with the program Crystal Explorer 17 (Turner et al., 2017) using established procedures described by Tan et al. (2019). In addition to the bright-red spots appearing near the sulfoxide-O2 and phthalazinone-H12 atoms on the Hirshfeld surface in Fig. 3(a),(b), the presence of diminutive red spots near methyl-C7 and benzene-H5 are indicative of intermolecular C-HÁ Á ÁC contacts as C-HÁ Á Á contacts are not preferred because of the V-shaped molecular geometry of (I). Also, the group of faint-red spots near alternate carbon atoms C10, C12, C14 and C16 of the phthalazinone-C 6 ring on the d norm -mapped Hirshfeld surface in Fig. 3 Table 2 and Fig. 2(a)] and is consistent with the significant contribution fromstacking between centrosymmetrically related phthalazinone-N 2 C 4 and C 6 rings, encompassing connections between phthalazinone-C 6 rings [3.6657 (9) Å with angle of inclination = 0.03 (7) ]. The involvement of the methyl-C8 atom in C-HÁ Á ÁO [to provide links between the chains shown in Fig. 2(b)] and C-HÁ Á ÁC contacts, Table 2, is highlighted in Fig. 3(c). The blue and red regions corresponding to positive and negative electrostatic potentials, respectively, on the Hirshfeld surface mapped over electrostatic potential shown in Fig. 4 Table 2 A summary of short interatomic contacts (Å ) in (I) a .

Contact
Distance Symmetry operation 2.20 x, À1 + y, z     The overall two-dimensional fingerprint plots for (I) and those delineated into HÁ Á ÁH, OÁ Á ÁH/HÁ Á ÁO, CÁ Á ÁH/HÁ Á ÁC and CÁ Á ÁC contacts are illustrated in Fig. 5(a)-(e), respectively; the percentage contributions from the different interatomic contacts to the Hirshfeld surfaces are summarized in Table 3. A short interatomic HÁ Á ÁH contact involving the phthalazinone-H12 and methyl-H9A atoms, Table 2, appears as a small peak at d e + d i $2.2 Å in the fingerprint plot delineated into HÁ Á ÁH contacts, Fig. 5(b). In the fingerprint plot delineated into OÁ Á ÁH/HÁ Á ÁO contacts illustrated in Fig. 5(c), a pair of forceps-like tips at d e + d i $2.3 Å , indicate the intermolecular C-HÁ Á ÁO interaction involving the phthalazinone-H12 and sulfoxide-O2 atoms, whereas the other interatomic OÁ Á ÁH/ HÁ Á ÁO contacts are merged within the plot and appear as a pair of intense blue spikes at d e + d i $2.8 Å . Despite the observation that intermolecular C-HÁ Á Á contacts are usually preferred by methyl groups, none are found involving those substituted at (C1-C6) benzene ring in the crystal due to the V-shaped geometry. Rather, the involvement of methyl-C7 and H5A atoms, and benzene-C5 and H7C atoms [to provide links between the chains shown in Fig. 2 Table 2, are characterized as the pair of forcepslike flat tips about d e + d i $2.8 Å in the fingerprint plot delineated into CÁ Á ÁH/HÁ Á ÁC contacts, Fig. 5(d). The presence of stacking interactions between symmetry-related phthalazinone-N 2 C 4 and C 6 rings is also evident as the arrow-shaped distribution of points around d e , d i $1.8 Å in the fingerprint plot delineated into CÁ Á ÁC contacts, Fig. 5(e). The contribution from other interatomic contacts, summarized in Table 2, show a negligible effect on the calculated Hirshfeld surface of (I).

Computational chemistry
The pairwise interaction energies between the molecules within the crystal of (I) were calculated by summing up four energy components, comprising electrostatic (E ele ), polarization (E pol ), dispersion (E dis ) and exchange-repulsion (E rep ) following Turner et al. (2017). The energies were obtained by using the wave function calculated at the B3LYP/6-31G(d,p) level of theory. The nature and strength of the intermolecular interactions in terms of their energies are quantitatively summarized in Table 4, where it is clear that the dispersive component makes the major contribution to the interaction energies in the crystal in the absence of conventional hydrogen bonding. It is revealed from the interaction energies listed in Table 4, that thestacking interaction between phthalazinone-N 2 C 4 and C 6 rings and the short interatomic O1Á Á ÁH14 contact have the greatest energy. The short interatomic C5Á Á ÁH7C, O3Á Á ÁH8A and C10Á Á ÁH8A contacts also have significant interaction energies due to their participation in inversion-related contacts. Lower energies, compared to above interactions, are calculated for the H12Á Á ÁH9A, C7Á Á ÁH5 and O1Á Á ÁH9C contacts. Fig. 6 illustrates the magnitudes of intermolecular energies represented graphically by energy frameworks to highlight the supramolecular architecture of the crystal through cylinders joining the centroids of molecular pairs using red, green and blue colour codes for the components E ele , E disp and E tot , respectively. The images emphasize the importance of dispersion interactions in the molecular packing.    Symmetry codes: (i) 1 À x, 1 À y, 2 À z; (ii) 1 À x, 2 À y, 1 À z; (iii) À x, 1 À y, 1 À z; (iv) x, À1 + y, z; (v) 1 + x, y, z.

Database survey
There is only a single direct analogue to (I) in the crystallographic literature, namely 2-(phenylsulfonyl)phthalazin-1(2H)-one (Asegbeloyin et al., 2018), (II). A comparison of key geometric parameters for (I) and (II) is given in Table 5. The data in Table 5 confirm the closeness of the salient bond lengths, but also show significant differences in the torsion angles about the N1-S1 and C1-S1 bonds, i.e. by up to 18 and 8 , respectively. These conformational differences are highlighted in the overlay diagram of Fig. 7 and in the dihedral angles between the aromatic residues of 83.26 (4) and 78.12 (4) for (I) and (II), respectively.

Synthesis and crystallization
2-{[2-(2,4,6-Trimethylphenylsulfonyl)hydrazinylidene]meth-yl}benzoic acid (III) was obtained by a method reported earlier (Asegbeloyin et al., 2018). Compound (I) was obtained from the following reaction. An ethanol solution (10 ml) of Dy(O 2 CCH 3 ) 3 Á4H 2 O (Wako Chemicals, Japan; 1 mmol, 411.692 mg) was added with constant stirring to an ethanol solution (20 ml) of (III) (1,039.2 mg, 3 mmol). The resulting mixture was refluxed for 3 h in an oil bath. The obtained colourless solution was concentrated to afford a colourless precipitate, which was filtered, dried under suction and further dried in vacuo over CaCl 2 . The precipitates were dissolved in ethanol, the resultant colourless solution was filtered and left at room temperature for 48 h to obtain colourless crystals of (I).

Figure 7
An overlay diagram for (I) (red image) and (II) (blue). The molecules have been overlapped so the hetero-rings are coincident.
research communications Table 6 Experimental details.  program(s) used to solve structure: SHELXS (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012), DIAMOND (Brandenburg, 2006); software used to prepare material for publication: 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.