Crystal structure of 2,6-dibenzylpyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetrathione

The title compound comprises a central pyromellitic diimide substituted with S atoms and terminal benzyl groups. In the crystal, adjacent molecules are linked by C—H⋯π interactions and short S⋯S contacts, forming a two-dimensional network parellel to the (110) plane.


Chemical context
Recently, pyromellitic diimide derivatives have been spotlighted due to their use in energy-storage materials (Nalluri et al. 2016). They also show potential applications in photovoltaic devices (Kanosue et al., 2016) and organic semiconductors (Zheng et al., 2008). Not only pyromellitic diimide derivatives, but also pyromellitic diimides substituted with sulfur have potential applications in organic semiconductors (Yang et al., 2015). We have reported copper(I) coordination polymers based on pyromellitic diimide derivatives (Park et al., 2011), which showed colour change owing to intermolecular halogen-interactions. In addition, we have found that reversible solvent exchange and crystal transformations were possible in the crystals (Kang et al., 2015). In an extension of previous research, we have synthesized the pyromellitic diimide in which the O atoms are replaced with S atoms, by the reaction of N,N 0 -dibenzylpyromellitic diimide with Lawesson's reagent, and report its crystal structure here.

Structural commentary
The molecular structure of the title compound consists of a central pyromellitic diimide substituted with S atoms and two terminal benzyl groups (Fig. 1). The molecule possesses a crystallographic inversion centre and thus the asymmetric unit ISSN 2056-9890 of the title compound is composed of half a molecule. The molecule exhibits an intramolecular C6-H6BÁ Á ÁS2 short contact (Table 1). In the molecule, the terminal phenyl groups point in opposite directions and their planes are tilted by 72.69 (8) with respect to the plane of the central arene ring, forming an elongated S-shaped molecule.

Supramolecular features
In the crystal, C6-H6BÁ Á ÁCg1 i (Cg1 is the centroid of the C7-C12 ring) interactions between neighbouring molecules generate a one-dimensional loop chain (yellow dashed lines in Fig. 2, and Table 1). Moreover, adjacent molecules are connected by a weak short S1Á Á Á S2 contact [3.5921 (10) Å ], resulting in the formation of a two-dimensional network (yellow and black dashed lines in Fig. 3).

Synthesis and crystallization
N,N 0 -Dibenzylpyromellitic diimide was synthesized by the reaction of pyromellitic dianhydride with 2-phenylethylamine according to the literature procedure of Im et al. (2017). To a stirred solution of N,N 0 -dibenzylpyromellitic diimide (0.25 g, 0.63 mmol) in anhydrous toluene (100 ml) was added Lawesson's reagent (2.00 g, 4.90 mmol), and the resulting mixture was stirred under reflux for 36 h. It was then cooled to room temperature and concentrated in vacuo, followed by purification by silica-gel flash column chromatography (CH 2 Cl 2 -nhexane, 1:3 v/v). Crystals suitable for X-ray diffaction analysis were obtained by slow evaporation of a dichloromethane solution of the title compound. The asymmetric unit of the title compound, with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as small spheres of arbitrary radius and yellow dashed lines represent intramolecular C-HÁ Á ÁS short contacts. Unlabelled atoms are generated by the symmetry operation (Àx + 2, Ày + 1, Àz). Table 1 Hydrogen-bond geometry (Å , ).
Cg1 is the centroid of the C7-C12 ring.

Figure 3
The packing diagram for the title compound, showing the twodimensional network formed by C-HÁ Á Á interactions (yellow dashed lines) and weak short SÁ Á ÁS contacts (black dashed lines). H atoms not involved in intermolecular interactions have been omitted for clarity.

2,6-Dibenzylpyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetrathione
Crystal data 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.