Crystal structure, Hirshfeld surface analysis and DFT studies of 2-(2,3-dihydro-1H-perimidin-2-yl)phenol

The asymmetric unit of the title compound contains two independent molecules, consisting of perimidine and phenol units, which are linked through an N—H⋯O hydrogen bond. Intramolecular O—H⋯N hydrogen bonds are observed in both independent molecules.

The asymmetric unit of the title compound, C 17 H 14 N 2 O, contains two independent molecules each consisting of perimidine and phenol units. The tricyclic perimidine units contain naphthalene ring systems and non-planar C 4 N 2 rings adopting envelope conformations with the C atoms of the NCN groups hinged by 44.11 (7) and 48.50 (6) with respect to the best planes of the other five atoms. Intramolecular O-HÁ Á ÁN hydrogen bonds may help to consolidate the molecular conformations. The two independent molecules are linked through an N-HÁ Á ÁO hydrogen bond. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from HÁ Á ÁH (52.9%) and HÁ Á ÁC/CÁ Á ÁH (39.5%) interactions. Hydrogen bonding and van der Waals interactions are the dominant interactions in the crystal packing. Density functional theory (DFT) optimized structures at the B3LYP/ 6-311 G(d,p) level are compared with the experimentally determined molecular structure in the solid state. The HOMO-LUMO behaviour was elucidated to determine the energy gap.
Perimidines are obtained by the condensation of 1,8-diaminonaphthalene with various carbonyl groups. As a continuation of our research into the development of new perimidine derivatives with potential pharmacological appli-cations, we have studied the reaction of the condensation of salicylaldehyde and 1,8-diaminonaphthalene in ether under agitation at room temperature to give the title compound in good yield. The title compound was obtained for the first time and characterized by single-crystal X-ray diffraction techniques as well as by Hirshfeld surface analysis. The results of the calculations by density functional theory (DFT), carried out at the B3LYP/6-311G (d,p) level, are compared with the experimentally determined molecular structure in the solid state.

Supramolecular features
In the crystal, the two molecules in the asymmetric unit are linked through an N-HÁ Á ÁO hydrogen bond (Table 1, Fig. 1).

Hirshfeld surface analysis
In order to visualize the intermolecular interactions in the crystal of the title compound, a Hirshfeld surface (HS) analysis (Hirshfeld, 1977;Spackman & Jayatilaka, 2009) was carried out by using Crystal Explorer 17.5 (Turner et al., 2017). In the HS plotted over d norm (Fig. 2), the white surface indicates contacts with distances equal to the sum of van der Waals radii, and the red and blue colours indicate distances shorter (in close contact) or longer (distinct contact) than the van der Waals radii, respectively (Venkatesan et al., 2016). The brightred spots indicate their roles as the respective donors and/or acceptors.
The shape-index of the HS is a tool to visualize thestacking by the presence of adjacent red and blue triangles; if Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.1813 to 1.6330 a.u.

Figure 1
The asymmetric unit of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
there are no adjacent red and/or blue triangles, then there are nointeractions. Fig. 3 clearly suggests that there are nointeractions in I. The overall two-dimensional fingerprint plot (McKinnon et al., 2007) is shown in Fig. 4a, and those delineated into HÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH, HÁ Á ÁN/ NÁ Á ÁH and CÁ Á ÁC contacts are illustrated in Fig. 4 b-f, respectively, together with their relative contributions to the Hirshfeld surface. The most important interaction is HÁ Á ÁH, contributing 52.9% to the overall crystal packing, which is reflected in Fig. 4b as widely scattered points of high density due to the large hydrogen content of the molecule, with the tip at d e = d i = 1.10 Å . The pair of characteristic wings in the fingerprint plot delineated into HÁ Á ÁC/CÁ Á ÁH contacts, The Hirshfeld surface analysis confirms the importance of H-atom contacts in establishing the packing. The large number of HÁ Á ÁH and HÁ Á ÁC/CÁ Á ÁH interactions suggest that van der Waals interactions and hydrogen bonding play the major roles in the crystal packing (Hathwar et al., 2015).

DFT calculations
The optimized structure of the title compound, I, in the gas phase was generated theoretically via density functional theory (DFT) using standard B3LYP functional and 6-311 G(d,p) basis-set calculations (Becke, 1993) as implemented in GAUSSIAN 09 (Frisch et al., 2009). The theoretical and experimental results were in good agreement ( Table 2). The highest-occupied molecular orbital (HOMO), acting as an electron donor, and the lowest-unoccupied molecular orbital (LUMO), acting as an electron acceptor, are very important parameters for quantum chemistry. When the energy gap is small, the molecule is highly polarizable and has high chemical reactivity. The DFT calculations provide some important information on the reactivity and site selectivity of the molecular framework. E HOMO and E LUMO , which clarify the inevitable charge-exchange collaboration inside the studied material, electronegativity (), hardness (), potential (), electrophilicity (!) and softness () are recorded in Table 3    HOMO to the LUMO energy level is shown in Fig. 6. The HOMO and LUMO are localized in the plane extending from the whole 2-(2,3-dihydro-1H-perimidin-2-yl)phenol ring. The energy band gap [ÁE = E LUMO -E HOMO ] of the molecule is 1.4933 eV, the frontier molecular orbital energies E HOMO and E LUMO being À3.2606 and À1.7673 eV, respectively.

Database survey
Similar perimidine derivatives have also been reported in which the groups at position 2 are almost coplanar with the perimidic nucleus. Examples related to the title compound, I, are II (Ghorbani, 2012), III (Fun et al., 2011), IV (Maloney et al., 2013), V (Cucciolito et al., 2013) and VI (Manimekalai et al., 2014), where III and V are most closely related while II, IV and VI are more distant relatives.

Synthesis and crystallization
0.35 mol (1.48 g) of 1,8-diaminonaphthalene and 18.8 mmol (2 ml) of salicylaldehyde were introduced into a 250 ml flask and 30 ml of ether were added thereto. The mixture was stirred magnetically for 3 days. The grey precipitate that formed was recovered by filtration, washed with ether, rinsed with ethanol and dried under Bü chner. The resulting brownish powder was recrystallized several times from ethanol to obtain colourless 2-(2,3-dihydro-1H-perimidin-2-yl)phenol product (R f = 0.70 in hexane/ethyl acetate (1:0.5), yield: 97% A significant quantity of the colourless monocrystalline product was obtained by the slow evaporation of the solvent after 15 days.

Refinement
Crystal data, data collection and structure refinement details are summarized in are summarized in Table 4. The H atoms of OH and NH groups were located in difference-Fourier maps and refined freely. The C-bound H atoms were positioned geometrically, with C-H = 0.93 Å (for aromatic H atoms) and 0.98 Å (for methine H atom) and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C).

Figure 6
The energy band gap of the title compound.  program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012). 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.