Synthesis, crystal structure and Hirshfeld surface analysis of 1-(12-bromododecyl)indoline-2,3-dione

The pendant dodecyl chain in the title compound adopts an all-trans conformation apart from the gauche terminal C—C—C—Br moiety.

In the title compound, C 20 H 28 BrNO 2 , the indoline portion is almost planar and the 12-bromododecyl chain adopts an all-trans conformation apart from the gauche terminal C-C-C-Br fragment.A micellar-like structure is generated in the crystal by C-H� � �O hydrogen bonds and �-stacking interactions between indolinedione head groups and intercalation of the 12-bromododecyl tails.The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H� � �H (58.9%),H� � �O/ O� � �H (17.9%) and H� � �Br/Br� � �H (9.5%) contacts.A density functional theory (DFT) optimized structure at the B3LYP/ 6-311 G(d,p) level shows good agreement with the experimentally determined molecular structure in the solid state.

Chemical context
The chemistry of isatin (1H-indole-2,3-dione; C 8 H 5 NO 2 ) and its derivatives has been studied extensively owing to its broad array of uses, particularly within the realms of organic synthesis and medicinal chemistry.The initial reports detailing the synthesis of isatin and its derivatives can be traced back to the early 19th century (Rharmili et al., 2023;Sonam & Kakkar, 2019).Nearly two centuries after the publication of these pioneering works, a comprehensive review highlighted the remarkable adaptability of this molecular fragment (Borad et al., 2014).Isatin derivatives have received much attention due to their properties such as anti-microbial (Pakravan et al., 2013), anti-mycobacterial (Li et al., 2018), anti-cancer (Khan et al., 2015) and corrosion-inhibitory activities (Verma et al., 2023).As a continuation of our studies in this area (Rharmili et al., 2023), we now report the synthesis, structure and Hirshfeld surface analysis and DFT computations of the title compound, C 20 H 28 BrNO 2 (I).

Structural commentary
As expected, the C1-C8/N1 bicyclic portion of (I) is almost planar (r.m.s.deviation of fitted atoms = 0.007 A ˚), with C8 showing the largest deviation from the mean plane, by 0.0130 (12) A ˚.The C10-C20 portion of the dodecyl chain is in an all-trans conformation (Fig. 1), as indicated by the moduli of the torsion angles involving these atoms being within 6 � of 180 � while the terminal C18-C19-C20-Br1 torsion angle is À 70.41 (19) � , indicating a gauche conformation.The sum of the bond angles about N1 is 359.9 � , suggesting sp 2 hybridization and involvement of the N lone pair in � bonding with the benzene ring.This is manifested in the C8-N1 bond length of 1.3595 (19) A ˚as compared with the C1-N1 distance of 1.4113 (19) A ˚.

Figure 1
The title molecule showing 50% probability ellipsoids.

Hirshfeld surface analysis and DFT calculations
To further visualize the intermolecular interactions in the crystal of (I), a Hirshfeld surface (HS) analysis was carried out by using Crystal Explorer 17.5 (Turner et al., 2017) (Fig. 4).The red spots indicate their roles as the respective donors and/or acceptors noted above.The overall two-dimensional finger-print plot, Fig. 5a, and those delineated into different contact types are illustrated in Fig. 5 b-m, respectively, together with their relative contributions to the Hirshfeld surface.The most important interaction is H� � �H contributing 58.9% to the overall crystal packing, which is reflected in Fig. 5b as widely scattered points of high density due to the large hydrogen content of the molecule with the tip at d e = d i = 0.98 A ˚.The H� � �O/O� � �H contacts contribute 17.9% to the HS, as may be seen in Fig. 5c, where the symmetric pair of spikes is observed with the tips at d e + d i = 2.34 A ˚.The wings of H� � �Br/Br� � �H contacts (Fig. 5d) are observed with the tips at d e + d i = 2.88 A ˚, and a contribution of 9.5% to the HS.In the presence of C-H� � �� interactions, the pair of characteristic wings in the fingerprint plot delineated into H� � �C/C� � �H contacts, Fig. 5e, has a 6.9% contribution to the HS with the tips at d e + d i = 3.08 A ˚.The C� � �C contacts (Fig. 5f), appearing as a bulletshaped distribution of points, have a contribution of 3.0% to the HS with the tip at d e = d i = 1.64A ˚.The tiny wing pair of C� � �Br/Br� � �C contacts (Fig. 5g) with a 2.0% contribution to the HS has the tips at d e + d i = 3.54 A ˚. Other contact types make a negligible contribution to the HS.
The theoretical structure of (I) was optimized in a gas-phase environment using density functional theory (DFT), using the B3LYP functional and 6-311G(d,p) basis-set calculations (Becke, 1992), giving an acceptable agreement between observed and calculated geometry (supplementary Table 1): the R 2 values of the bond lengths and bond angles of (I) were calculated to be 0.998 and 0.991, respectively.The terminal C18-C19-C20-Br1 grouping has observed and calculated torsion angles of À 70.41 (19) and 69.06 � , respectively.The frontier orbitals of (I) are depicted in supplementary Fig. 1 and the HOMO-LUMO gap of the molecule is about 3.57 eV (supplementary Table 2).

Database survey
A search conducted in the Cambridge Structural Database (CSD; Version 5.42, last updated in May 2023; Groom et al., 2016) targeting N-substituted isatin derivatives yielded a total of 58 results.Among these, there were five reports on the structure of isatin itself and four instances of the structure of N-methylisatin.Thirteen of these structures featured an alkyl chain consisting of two or more carbon atoms.The compound most closely related to the title compound is 1-(3-bromopropyl)-1H-indole-2,3-dione (CSD refcode AKOBIN; Qachchachi et al., 2016), which also features a gauche terminal C-C-C-Br grouping.

Synthesis and crystallization
To a solution of 1H-indoline-2,3-dione (2.0 mmol), potassium carbonate (4.0 mmol) and tetra-n-butylammoniumbromide (0.20 mmol) in dimethylformamide (20 ml) was added 1,12dibromododecane (2.2 mmol) and the mixture was then left to stir for 18 h at room temperature.Following salt filtration, the solvent was evaporated at low pressure, and the resulting residue was dissolved in dichloromethane.The organic phase  was then dried over Na 2 SO 4 and concentrated.The resulting mixture was chromatographed using a silica gel column with hexane/ethylacetate as the eluent (3/1).Single crystals of the title compound suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms attached to carbon were placed in calculated positions (C-H = 0.95-0.99A ˚).All were included as riding contributions with isotropic displacement parameters 1.2-1.5 times those of the attached atoms.(Sheldrick, 2008).

Special details
Experimental.The diffraction data were obtained from 14 sets of frames, each of width 0.5° in ω or φ, collected with scan parameters determined by the "strategy" routine in APEX4.The scan time was θ-dependent and ranged from 3 to 12 sec/frame.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.
Refinement.Refinement of F 2 against ALL reflections.The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 .The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement.R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.H-atoms attached to carbon were placed in calculated positions (C-H = 0.95 -0.99 Å).All were included as riding contributions with isotropic displacement parameters 1.2 -1.5 times those of the attached atoms. Fractional

Figure 2 A
Figure 2 A portion of one layer projected onto (201) with C-H� � �O hydrogen bonds depicted by dashed lines.Non-interacting hydrogen atoms are omitted for clarity.

Figure 3
Figure 3Packing viewed along the b-axis direction with C-H� � �O hydrogen bonds and slipped �-stacking interactions depicted, respectively, by black and dark pink dashed lines.Non-interacting hydrogen atoms are omitted for clarity.

Figure 4
Figure 4View of the three-dimensional Hirshfeld surface of the title compound, plotted over d norm in the range of À 0.18 to 1.38 a.u.

Table 2
Experimental details.