Crystal structure, Hirshfeld surface analysis and interaction energy and DFT studies of 2-(2,3-dihydro-1H-perimidin-2-yl)-6-methoxyphenol

The title compound consists of perimidin and methoxyphenol units. In the crystal, O—HPhnl⋯NPrmdn and N—HPrmdn⋯OPhnl (Phnl = phenol and Prmdn = perimidine) hydrogen bonds link the molecules into infinite chains along the b-axis direction. C—H⋯π interactions may further stabilize the crystal structure.

The title compound, C 18 H 16 N 2 O 2 , consists of perimidine and methoxyphenol units, where the tricyclic perimidine unit contains a naphthalene ring system and a non-planar C 4 N 2 ring adopting an envelope conformation with the NCN group hinged by 47.44 (7) with respect to the best plane of the other five atoms. In the crystal, O-H Phnl Á Á ÁN Prmdn and N-H Prmdn Á Á ÁO Phnl (Phnl = phenol and Prmdn = perimidine) hydrogen bonds link the molecules into infinite chains along the baxis direction. Weak C-HÁ Á Á interactions may further stabilize the crystal structure. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from HÁ Á ÁH (49.0%), HÁ Á ÁC/CÁ Á ÁH (35.8%) and HÁ Á ÁO/OÁ Á ÁH (12.0%) interactions. Hydrogen bonding and van der Waals interactions are the dominant interactions in the crystal packing. Computational chemistry indicates that in the crystal, the O-H Phnl Á Á ÁN Prmdn and N-H Prmdn Á Á ÁO Phnl hydrogen-bond energies are 58.4 and 38.0 kJ mol À1 , respectively. 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.

Chemical context
Six-membered heterocyclic compounds carrying two nitrogen atoms have been widely studied (Aly & El-Shaieb, 2004;Koca et al., 2012;Zhao et al., 2012;Baranov & Fadeev, 2016;Lahmidi et al., 2018). Perimidine derivatives (perinaphtho-fused perimidine ring systems) in particular have aroused a lot of interest because of their applications in photophysics (Del Valle et al., 1997) and their use as colouring matters for polyester fibers (Claramunt et al., 1995) and as fluorescent materials (Varsha et al., 2010). These molecules have a wide range of biological applications (Dzieduszycka et al., 2002), indicating that the perimidine group is a potentially useful model in medicinal chemistry research and therapeutic applications. In coordination chemistry, perimidine derivatives have been studied for their interesting catalytic activities (Cucciolito et al., 2013a;Akıncı et al., 2014) as well as in the field of corrosion inhibition (He et al., 2018). As a continuation ISSN 2056-9890 of our research on the development of new perimidine derivatives with potential pharmacological applications, we studied the condensation reaction of ortho-vanillin and 1,8diaminonaphthalene in ether under agitation at room temperature, which gave the title compound, 2-(2,3-dihydro-1H-perimidin-2-yl)-6-methoxyphenol, in good yield. We report herein the synthesis, the molecular and crystal structures along with Hirshfeld surface analysis and computational calculations of the title compound, (I).

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. 3), 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) Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A partial packing diagram viewed along the a-axis direction with O-H Phnl Á Á ÁN Prmdn and N-H Prmdn Á Á ÁO Phnl (Phnl = phenol and Prmdn = perimidine) hydrogen bonds shown as dashed lines. H-atoms not included in hydrogen bonding have been omitted for clarity.

Figure 1
The asymmetric unit of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
donor and/or acceptor; it also appears as blue and red regions corresponding to positive and negative potentials on the HS mapped over electrostatic potential (Spackman et al., 2008;Jayatilaka et al., 2005)  View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.4133 to 1.3883 a.u.

Figure 4
View of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potential energy in the range À0.0500 to 0.0500 a.u. using the STO-3 G basis set at the Hartree-Fock level of theory. Hydrogen-bond donors and acceptors are shown as blue and red regions around the atoms corresponding to positive and negative potentials, respectively.

Figure 6
The full two-dimensional fingerprint plots for the title compound

Figure 5
Hirshfeld surface of the title compound plotted over shape-index.
HÁ Á ÁN/NÁ Á ÁH, CÁ Á ÁC and OÁ Á ÁC/CÁ Á ÁO contacts (McKinnon et al., 2007) are illustrated in Fig. 6 b-g, respectively, together with their relative contributions to the Hirshfeld surface. The most important interaction is HÁ Á ÁH contributing 49.0% to the overall crystal packing, which is reflected in Fig. 6b as widely scattered points of high density due to the large hydrogenatom content of the molecule with the tip at d e = d i = 1.20 Å .
In the presence of C-HÁ Á Á interactions, the pair of characteristic wings in the fingerprint plot, Fig. 6c, delineated into HÁ Á ÁC/CÁ Á ÁH contacts (  Fig. 7a-c, respectively. The Hirshfeld surface analysis confirms the importance of H-atom contacts in establishing the packing. The large number of HÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH and HÁ Á ÁO/OÁ 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 3)   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 clarify the inevitable charge-exchange collaboration inside the studied material, electronegativity (), hardness (), potential (), electrophilicity (!) and softness () are recorded in Table 4. The significance of and is for the evaluation of both the reactivity and stability. The electron transition from the HOMO to the LUMO energy level is shown in Fig. 8. The HOMO and LUMO are localized in the plane extending from the whole 2-(2,3-dihydro-1H-perimidin-2-yl)-6-methoxyphenol ring.

Synthesis and crystallization
The title compound, (I), was synthesized from the condensation of ortho-vanillin (3 mmol) and 1,8-diaminonaphthalene (4 mmol) in ether (30 ml) under agitation at room temperature. Brown single crystals were obtained by the slow evaporation of the acetone solvent after 15 days (yield: 75%).

Refinement
Crystal data, data collection and structure refinement details are summarized in The energy band gap of the title compound, (I).

2-(2,3-Dihydro-1H-perimidin-2-yl)-6-methoxyphenol
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.