Crystal structure and Hirshfeld surface analysis of 4-[4-(1H-benzo[d]imidazol-2-yl)phenoxy]phthalonitrile dimethyl sulfoxide monosolvate

The synthesis, structural characterization and Hirshfeld surface analysis of 4-[4-(1H-benzo[d]imidazol-2-yl)phenoxy]phthalonitrile, a substituted phthalonitrile derivative carrying a benzimidazole functional group, are reported.

This work presents the synthesis and structural characterization of imidazol-2-yl)phenoxy]phthalonitrile, a phthalonitrile derivative carrying a benzimidazole moiety. The compound crystallizes as its dimethyl sulfoxide monosolvate, C 21 H 12 N 4 OÁ(CH 3 ) 2 SO. The dihedral angle between the two fused rings in the heterocyclic ring system is 2.11 (1) , while the phenyl ring attached to the imidazole moiety is inclined by 20.7 (1) to the latter. In the crystal structure, adjacent molecules are connected by pairs of weak intermolecular C-HÁ Á ÁN hydrogen bonds into inversion dimers. N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds with R 2 1 (7) graph-set motifs are also formed between the organic molecule and the disordered dimethyl sulfoxide solvent [occupancy ratio of 0.623 (5):0.377 (5) for the two sites of the sulfur atom]. Hirshfeld surface analysis and fingerprint plots were used to investigate the intermolecular interactions in the crystalline state.

Chemical context
Benzimidazole and its derivatives are some of the oldest and chemically most-studied nitrogen-containing aromatic heterocyclic compounds (Srestha et al., 2014). They have a wide range of applications in medicinal chemistry and in biological processes including as anticancer, antiulcer, antifungal and anti-inflammatory agents, and exhibit antimycobacterial and antioxidant activities (El Rashedy & Aboul-Enein, 2013;Gaba et al., 2014;Kathiravan et al., 2012). They are also used as ligands with fluorescent properties. The fluorescent characteristic of these compounds can be changed by substitution or derivatization of different groups at the NH position of the benzimidazole skeleton.
Phthalonitrile derivatives are some of the most widely used precursors for the preparation of phthalocyanines (Pc). The preparation of phthalocyanines is frequently carried out by a cyclotetramerization reaction of phthalonitriles. The synthesis of the latter compound family, carrying different functional groups, leads to functionalized phthalocyanines that are of great importance with respect to new molecular materials and targeted applications such as catalysis, liquid crystals, photosensitizers for photodynamic therapy (PDT), non-linear optics, nanotechnology or dye-sensitized solar cells (Torre et al., 2004;Martínez-Díaz et al., 2011). In this context, we have recently described a model study, i.e. the synthesis, characterization and Hirshfeld surface analysis of zinc phthalocyanines carrying benzimidazole groups through oxygen bridges to a Zn-Pc core (Sen et al., 2018b). Here we report the synthesis, structural characterization and Hirshfeld surface analysis of a related ligand that crystallizes as its dimethylsulfoxide monosolvate, C 21 H 12 N 4 OÁ(CH 3 ) 2 SO.

Structural commentary
The molecular components of the title compound are shown in Fig. 1. The molecular structure of the phthalonitrile derivative is constructed from three ring systems, viz. a central phenoxy ring, a terminal phthalonitrile system and a terminal benzimidazole ring. The bond lengths of the cyano groups, 1.132 (6) and 1.137 (6) Å , for C21 N4 and C20 N3, respectively, conform well with literature values (Saraçog lu et al., 2011). The corresponding C-C N angles [179.4 (6) and 177.9 (7) ] are almost linear and are also in good agreement with literature values (Saraçog lu et al., 2011;Sen et al., 2018a). The C-C bond lengths of the phenyl rings are in the normal range of 1.356 (5)-1.395 (6) Å , i.e. characteristic of a delocalized system. The dihedral angle of 2.11 (1) between the fused C1-C6 and C5/N2/C7/N1/C6 rings in the heterocycle indicate a minute deviation from planarity, whereas the attached C8-C13 ring is inclined by 20.7 (1) to the C5/N2/C7/N1/C6 ring plane.

Supramolecular features
In the crystal structure, N2-H2Á Á ÁO2 and C9-H9Á Á ÁO2 intermolecular hydrogen bonding interactions with an R 1 2 (7) graph-set motif are present, whereby the O2 atom acts as an acceptor in both cases (Fig. 1). There are also weak intermolecular N2-H2Á Á ÁS1A interactions between the the N-H group of the imidazole ring and the disordered dimethyl sulfate solvent, and a C23-H23DÁ Á ÁN4 interaction between one of the methyl groups of the dimethyl sulfoxide solvent and Symmetry code: (i) Àx þ 1 2 ; y À 1 2 ; z þ 1 2 .

Figure 1
The molecular structure of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds (  Fig. 2). These interactions lead to the formation of a three-dimensional supramolecular network.  Sen et al., 2018a). In these structures, the C-O bond lengths vary from 1.363-1.407 Å . In the title molecule, the corresponding bond lengths are 1.367 (5) and 1.406 (4) Å , respectively. In all these structures, the molecules are linked into chains by C-HÁ Á ÁN hydrogen bonds.

Hirshfeld surface analysis
The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) and the associated two-dimensional fingerprint plots (McKinnon et al., 2007) were performed with Crystal-Explorer17 (Turner et al., 2017). The Hirshfeld surfaces were generated using a standard (high) surface resolution with the three-dimensional surfaces mapped over d norm (Fig. 3). For the title molecule, the HÁ Á ÁH interactions appear in the middle of the scattered points in the fingerprint plots with a contribution to the overall Hirshfeld surface of 36.1% (Fig. 4)  The Hirshfeld surface of the title compound mapped with d norm in the range À0.6328 to 1.3784 a.u.

Figure 5
A view of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potentials in the range À0.0893 to 0.1930 a.u.

Figure 4
Two-dimensional fingerprint plots with a d norm view of all interactions in the title compound, and subdivided into HÁ Á ÁH (36.1%), NÁ Á ÁH/HÁ Á ÁN(23.6%), contribution from the NÁ Á ÁH/HÁ Á ÁN contacts, corresponding to the C-HÁ Á ÁN interactions, is represented by a pair of sharp spikes characteristic of a rather strong hydrogen-bonding interaction (23.6%). The whole fingerprint region and all other interactions are displayed in Fig. 4. In particular, the OÁ Á ÁH/HÁ Á ÁO contacts indicate the presence of intermolecular C-HÁ Á ÁO and N-HÁ Á ÁO interactions.
A view of the molecular electrostatic potential for the title compound, using the STO-3G basis set at the Hartree-Fock level of theory, is shown in Fig. 5. The N-HÁ Á ÁN and C-HÁ Á ÁN hydrogen-bond donor and acceptor groups are shown as blue and red areas around the atoms related with positive (hydrogen-bond donors) and negative (hydrogen-bond acceptors) electrostatic potentials, respectively.

Synthesis and crystallization
2-(4-Hydroxy-phenyl)-benzimidazole (1.2 g, 5.71 mmol), which was synthesized by the reaction of o-phenylenediamine and 4-hydroxybenzaldehyde, and 4-nitrophthalonitrile (0.989 g, 5.71 mmol) were dissolved in DMF (15 ml) and degassed by argon in a dual-bank vacuum-gas manifold system. After stirring for 15 min, finely ground anhydrous K 2 CO 3 (0.790 g, 5.71 mmol) was added portion-wise over 2 h under stirring. The suspension solution was maintained at 333 K for 24 h. After completion of the reaction, the crude product was precipitated by pouring into ice-water. The precipitate was collected by filtration, washed with hot water, ethanol, diethyl ether and was finally dried in vacuo. The desired compound was obtained in sufficient purity. The obtained spectroscopic data are accordance with the literature (Khan et al., 2009). Single crystals for structure analysis were obtained from slow evaporation of a DMSO solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.93 Å for aromatic groups, with N-H = 0.86 Å for the imidazole moiety and with 0.96 Å for methyl groups. U iso (H) values were constrained to 1.2-1.5 U eq of their carrier atoms. The sulfur atom of the dimethylsulfate solvent is disordered over two sites (S1A and S1B), with an occupancy ratio of 0.623 (5):0.377 (5).    (Farrugia, 2012) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL2018 (Sheldrick, 2015b), WinGX (Farrugia, 2012) and PLATON (Spek, 2009).

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.