Crystal structure and Hirshfeld surface analysis of 2-phenyl-1H-phenanthro[9,10-d]imidazol-3-ium benzoate

The title compound exists in the crystal as a dimer of ion pairs. Hydrogen bonding and weak π–π interactions along with N—H⋯π interactions are involved in consolidating this cluster. The three-dimensional crystal structure consists of stepped stacks of dimers of ion pairs associated by C—H⋯π(ring) and slipped π-stacking interactions.


Chemical context
When phenanthrene is substituted by a heterocyclic moiety, its intermolecular charge-transfer ability is increased . Such a donor--acceptor (D--A) arrangement has tunable properties that can be controlled by suitable substituents . The presence of a heteroatom such as N, O or S may give electron-rich heterocycles (thiophene, pyrrole, or furan) or electron-deficient heterocycles (pyridine, phenanthroline) . The dipole moment and max can be modulated by the selection of D and A. Thus the photophysical properties can be controlled . The inclusion of heterocycles enhances the polarizability, thermal and chemical stabilities of such adducts. Theconjugated heterocyclic systems increase delocalization, thus enhancing the stability and photophysical properties , Zhang et al., 2012. By proper selection of the heterocyclic substituent, good fluorescence with higher sensitivity can be achieved (Li et al., 2016;Huang et al., 2012). The synthesis of selective chromo-fluorogenic sensors for anions, cations and neutral molecules can be achieved (Chou et al., 2012;Zhuang et al., 2012). Herein we report the crystal structure of the title compound, which was synthesized from 2-phenyl-1H-phenanthro[9,10-d]imidazole and benzoic acid. ISSN 2056-9890

Hirshfeld surface analysis
The Hirshfeld surfaces provide an extended qualitative and quantitative analysis of the interactions between the constituents of the co-crystal. The analysis shows the presence of C-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds leading to multidirectional interactions to form the three-dimensional structure. The red spots in the Hirshfeld surface ( Fig. 4) are centered on the N1-H1Á Á ÁO1, C10-H10Á Á ÁO1 and C28-H28Á Á ÁO1 interactions of the benzoate ion with the phenanthrene and with the N-H of the imidazole. Their bond lengths are 1.77, 2.40, and 2.48 Å , respectively. The fingerprint plots (Fig. 5)  Unit A consisting of two entities each of benzoate ions and M1 moieties, linked by hydrogen bonds andinteractions. Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
Supramolecular structure showing A units stacked over adjacent rows of A units running perpendicular to each other.

Figure 1
The molecular structure of the title compound with atom labelling. The dashed line indicates the N-HÁ Á ÁO hydrogen bond. Displacement ellipsoids are drawn at the 50% probability level.

Synthesis and crystallization
A condensation reaction was performed between equimolar quantities of phenanthrene-9,10-dione and benzaldehyde. 1 mmol of phenanthrene-9,10-dione, 1 mmol of benzaldehyde, 5 mmol of ammonium acetate and 30 mL of glacial acetic acid were added to single-neck 100 mL round-bottom flask. The mixture was refluxed for 12 h under nitrogen. After completion of the reaction, the reaction mixture was cooled to room temperature and then 50 mL of deionized cold water were added. The product precipitated out as pale-brown solid. The solid product was filtered, washed with deionized water and dried in a vacuum oven to give 2-phenyl-1H-phenanthro[9,10d]imidazole (M1) as the final product. Crystals were prepared using 20 mg of M1 and 20 mg of benzoic acid dissolved in 5mL of ethanol. The clear solution was left undisturbed for crystallization. Fine crystals were obtained after 15 days.

Refinement
Crystal data, data collection and structure refinement details are summarized in

Figure 4
View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm . program(s) used to solve structure: SHELXT2018/3 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2020); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2020). 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.