Crystal structure, Hirshfeld surface analysis and interaction energy and DFT studies of 4-[(prop-2-en-1-yloxy)methyl]-3,6-bis(pyridin-2-yl)pyridazine

The title compound consists of a 3,6-bis(pyridin-2-yl)pyridazine unit linked to a 4-[(prop-2-en-1-yloxy)methyl] moiety. The pyridine-2-yl rings are rotated slightly out of the plane of the pyridazine ring. In the crystal, C—H⋯N hydrogen bonds and C—H⋯π interactions link the molecules, forming deeply corrugated layers approximately parallel to the bc plane and stacked along the a-axis direction.

The title compound, C 18 H 16 N 4 O, consists of a 3,6-bis(pyridin-2-yl)pyridazine moiety linked to a 4-[(prop-2-en-1-yloxy)methyl] group. The pyridine-2-yl rings are oriented at a dihedral angle of 17.34 (4) and are rotated slightly out of the plane of the pyridazine ring. In the crystal, C-H Pyrd Á Á ÁN Pyrdz (Pyrd = pyridine and Pyrdz = pyridazine) hydrogen bonds and C-H Prpoxy Á Á Á (Prpoxy = prop-2en-1-yloxy) interactions link the molecules, forming deeply corrugated layers approximately parallel to the bc plane and stacked along the a-axis direction. Hirshfeld surface analysis indicates that the most important contributions for the crystal packing are from HÁ Á ÁH (48.5%), HÁ Á ÁC/CÁ Á ÁH (26.0%) and HÁ Á ÁN/ NÁ Á ÁH (17.1%) contacts, hydrogen bonding and van der Waals interactions being the dominant interactions in the crystal packing. Computational chemistry indicates that in the crystal, the C-H Pyrd Á Á ÁN Pyrdz hydrogen-bond energy is 64.3 kJ mol À1 . 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.

Figure 2
A partial packing diagram viewed along the a-axis direction with C-H Pyrd Á Á ÁN Pyrdz hydrogen bonds and C-H Prpoxy Á Á Á interactions shown, respectively, as light blue and green dashed lines.

Figure 3
A partial packing diagram viewed along the c-axis direction with C-H Pyrd Á Á ÁN Pyrdz hydrogen bonds and C-H Prpoxy Á Á Á interactions shown, respectively, as light-blue and green dashed lines.

Hirshfeld surface analysis
In order to visualize the intermolecular interactions, a Hirshfeld surface (HS) analysis (Hirshfeld, 1977;Spackman & Jayatilaka, 2009) was carried out by using CrystalExplorer17.5 (Turner et al., 2017). In the HS plotted over d norm (Fig. 4), white areas indicate contacts with distances equal to the sum of van der Waals radii, and red and blue areas indicate distances shorter (in close contact) or longer (distinct contact) than the van der Waals radii (Venkatesan et al., 2016). The bright-red spots appearing near N1 and hydrogen atoms H8 and H15B indicate their roles as donors and/or acceptors; they also appear 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) shown in Fig. 5. The blue regions indicate positive electrostatic potential (hydrogen-bond donors), while the red regions indicate negative electrostatic potential (hydrogen-bond acceptors). The shape-index of the HS is a tool to visualizestacking by the presence of adjacent red and blue triangles; if there are no adjacent red and/or blue triangles, then there are nointeractions. 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, respectively, around the atoms, corresponding to positive and negative potentials.

Figure 6
Hirshfeld surface of the title compound plotted over shape-index.

Figure 4
View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.1063 to 1.1444 a.u.
respectively, together with their relative contributions to the Hirshfeld surface. The most important interaction is HÁ Á ÁH (Table 2), contributing 48.5% to the overall crystal packing, which is reflected in Fig. 7b Fig. 8a--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 H Á Á Á N/NÁ 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 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)   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, and are given in Table 4 along with the electronegativity (), hardness (), potential (), electrophilicity (!) and softness (). The significance of and is to evaluate both the reac-tivity and stability. The electron transition from the HOMO to the LUMO energy level is shown in Fig. 9. The HOMO and LUMO are localized in the plane extending from the whole 4-[(prop-2-en-1-yloxy)methyl]-3,6-bis(pyridin-2-yl)pyridazine ring. The energy band gap [ÁE = E LUMO À E HOMO ] of the molecule is 4.1539 eV, and the frontier molecular orbital energies, E HOMO and E LUMO are À6.0597 and À1.9058 eV, respectively.

Synthesis and crystallization
THF (20 ml), [3,6-di(pyridin-2-yl)pyridazin-4-yl]methanol (3 mmol), 1.8 eq. of NaH and 0.04 eq. of 18-crown ether A were added to a conical flask and stirred for 10 min at room temperature. Then 1.2 eq of propargyl allyl chloride was added to the reaction mixture and stirred for 48 h. The solvent was then evaporated off and the required organic compound was obtained by liquid-liquid extraction using dichloromethane. The organic phase was dried with sodium sulfate (Na 2 SO 4 ), and then evaporated. The product obtained was separated by chromatography on a column of silica gel. The isolated solid was recrystallized from hexane-dichloromethane (1:1) to afford colourless crystals (yield: 87%, m.p. 376 K).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. The hydrogen atoms were located in a difference-Fourier map and refined freely.  Table 3 Comparison of the selected (X-ray and DFT) geometric data (Å , ).

4-[(Prop-2-en-1-yloxy)methyl]-3,6-bis(pyridin-2-yl)pyridazine
Crystal data Extinction correction: SHELXL2018 (Sheldrick, 2015b), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0046 (5) 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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.