Syntheses and crystal structures of 2-(p-tolyl)-1H-perimidine hemihydrate and 1-methyl-2-(p-tolyl)-1H-perimidine

N-methylation of the perimidine core results in an increase of the interplanar angle between the perimidine and aryl rings. The crystal packing of the unsubstituted perimidine is formed by hydrogen bonding and π–π stacking while molecules of its N-substituted analog are assembled by C—H⋯π interactions.


Chemical context
Perimidines have found applications in industry as dyes and pigments because of their finely tunable optical properties (Pozharskii et al., 2020). The introduction of electrondonating/withdrawing groups to the perimidine system dramatically affects its electronic structure and allows the color as well as color intensity of the perimidine to be varied. Additionally, a significant deepening of the color of perimidines can be achieved by decorating them with aromatic rings at position 2 while their optical characteristics can be modulated by varying the N-substituent (Sahiba & Agarwal, 2020). Recently, we have studied the effect of the N-substituent(s) on the structures of 2-(pyridin-2-yl)-1-H-perimidines (Kalle et al., 2021). Herein, we report structural studies of 1-H-2-(p-tolyl)perimidine hemihydrate (1) and 1-methyl-2-(p-tolyl)-perimidine (2).

Supramolecular features
Recrystallization of 1 from toluene, dichloromethane, chloroform or methanol gives crystals having an identical structure. An X-ray study of the crystals grown from hot toluene shows that compound 1 crystallizes as a hemihydrate in which the solvent molecule plays a dominant role in the crystal packing. Each water molecule, located at the intersection of three twofold rotation axes (Wyckoff position 8a; point group symmetry 222), arranges four 2-(p-tolyl)perimidines by mutual O-HÁ Á ÁN and N-HÁ Á ÁO interactions involving the O1 and N1 atoms as well as disordered hydrogen atoms H1 and H1B (Fig. 3, Table 1). These hydrogen-bonded associates containing the included water molecule are additionally stabilized bycontacts between the aromatic units [d(C1Á Á ÁN1-C12 centroid ) = 3.3276 (11) Å , centroid-centroid shift of 1.591 (1) Å , d(C7Á Á ÁC1-C5 centroid ) = 3.5950 (11) Å , centroid-centroid shift of 1.433 (1) Å ]. The same interactions combine the associates into infinite stacks along the a axis, forming two-dimensional structural arrays. The alignment of the arrays along the c axis by weak van der Waals interactions between perimidine C9-H9 and C10-H10 bonds and the methyl group (C4) of the p-tolyl ring completes the crystal packing of 1.

Figure 1
Molecular structure of 1-H-2-(p-tolyl)-perimidine (1) (18) ], forming arrays in the ab plane. The three-dimensional crystal packing is organized by the alignment of the arrays along the c axis by weak van der Waals interactions in the same manner as in the crystal of 1. It is interesting that compound 2, in contrast to the parent perimidine 1, crystallizes without notableinteractions.

Synthesis and crystallization
The title compounds were prepared as follows: 1-H-2-(p-tolyl)perimidine (1). A mixture of 1,8-diaminonaphthalene (1.58 g, 0.01 mol), 4-methylbenzaldehyde (1.18 ml, 0.01 mol) and sodium metabisulfite (5.7 g, 0.03 mol) in ethanol (40 ml) was refluxed under Ar for 2 h. The reaction mixture was cooled, filtered and the filtrate was evaporated to dryness and washed with water. The crude solid was recrystallized from toluene and dried in vacuo. Yield 2.20 g (85%). Single crystals suitable for X-ray analysis were grown from hot toluene. 1-Methyl-2-(p-tolyl)perimidine (2). To a mixture of (1) (0.258 g, 1.0 mmol), solid KOH (0.056 g, 1.0 mmol) and anhydrous K 2 CO 3 (0.138 g, 1.0 mmol) in anhydrous Ar-saturated acetonitrile methyl iodide (0.062 ml, 1.0 mmol) were added dropwise upon stirring and the resulting suspension was heated at 323 K for 1 h and then at room temperature for 1 h. The reaction mixture was evaporated to dryness and the crude product was purified by column chromatography (eluent hexane/ethyl acetate 1/1 ! 1/5 v/v), recrystallized from a mixture of toluene/hexane and dried in vacuo. Yield 125 mg (46%). Single crystals suitable for X-ray analysis were grown by slow evaporation of the solvent from a solution of the substance in toluene.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All C-H hydrogen atoms in the structures of 1 and 2 were placed in calculated positions and refined using a riding model [C-H = 0.94-0.97 Å with U iso (H) = 1.2-1.5U eq (C)]. N-H and O-H hydrogen atoms (structure 1) were located in difference electron-density maps and were refined with a fixed occupancy of 0.5. para-Methyl groups in both crystallographically independent molecules of 2 were found to be rotationally disordered with occupancy ratios of 0.6/0.4 and 0.7/0.3. The same group in the structure of 1 was similarly disordered with an occupancy ratio of 0.5/0.5. The SIMU instruction was used to restrain the U ij components of the neighboring C6 and N1 atoms in the structure of 1. The most disagreeable reflections with an error/s.u. of more than 10 (0 0 4 in the structure of 1; 5 0 34 and 6 1 33 in the structure of 2) were omitted using the OMIT instruction in SHELXL (Sheldrick, 2015).   Computer programs: APEX3 and SAINT (Bruker, 2017), SHELXS (Sheldrick, 2008), SHELXL (Sheldrick, 2015) and OLEX2 (Dolomanov et al., 2009 For both structures, data collection: APEX3 (Bruker, 2017); cell refinement: SAINT (Bruker, 2017); data reduction: SAINT (Bruker, 2017); program(s) used to solve structure: SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL (Sheldrick, 2015); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009). T min = 0.672, T max = 0.746 14708 measured reflections 2138 independent reflections 1630 reflections with I > 2σ(I) 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.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (