Crystal structure, Hirshfeld surface analysis and interaction energy and DFT studies of methyl 4-[3,6-bis(pyridin-2-yl)pyridazin-4-yl]benzoate

The pyridazine ring deviates slightly from planarity. In the crystal, ribbons consisting of inversion-related chains of molecules extending along the a-axis direction are formed by C—HMthy⋯OCarbx (Mthy = methyl and Carbx = carboxylate) hydrogen bonds. The ribbons are connected into layers parallel to the bc plane by inversion-related C—HBnz⋯π(ring) interactions.


Supramolecular features
In the crystal, chains of molecules extending along the a-axis direction are formed by C22-H22CÁ Á ÁO1 v hydrogen bonds (Table 1). Inversion-related chains are connected into ribbons by C22-H22BÁ Á ÁO1 iv hydrogen bonds (Table 1) and the ribbons are joined into stepped layers approximately parallel to (011) by inversion-related pairs of C19-H19Á Á ÁCg1 i interactions, where Cg1 is the centroid of pyridine ring A (Table 1 Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.1417 to 1.3796 a.u.

Figure 1
The molecular structure of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A partial packing diagram showing two chains connnected by C-HÁ Á Á(ring) interactions (green dashed lines

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 CrystalExplorer (Version 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 the 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 bright-red spots appearing near atoms O1 and H22B and H22C indicate their roles as the respective 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), as shown in Fig. 4. The blue regions indicate the positive electrostatic potential (hydrogen-bond donors), while the red regions indicate the negative electrostatic potential (hydrogen-bond acceptors). The shape-index of the HS is a tool to visualize thestacking by the presence of adjacent red and blue triangles; if there are no adjacent red and/or blue triangles, then there are nointeractions. Fig. 5 clearly suggests that there are nointeractions in (I). The overall two-dimensional fingerprint plot ( Fig. 6a) and those delineated into HÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH, HÁ Á ÁN/NÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH, CÁ Á ÁC and CÁ Á ÁN/NÁ Á ÁC contacts (McKinnon et al., 2007) are illustrated in Figs. 6 (b)-(g), respectively, together with their relative contributions to the Hirshfeld surface. The most important interaction is HÁ Á ÁH contributing 39.7% to the overall crystal packing, which is reflected in Fig. 6(b) 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 , due to the short interatomic HÁ Á ÁH contacts (Table 2). Due to the presence of C-HÁ Á Á interactions, a 27.5% contribution to the HS arises from the HÁ Á ÁC/ CÁ Á ÁH contacts (Table 2) which are viewed as pairs of spikes in the fingerprint plot shown in Fig. 6(c) with the tips at d e + d i = 2.75 Å . The pair of scattered points of wings resulting in the fingerprint plots delineated into HÁ Á ÁN/NÁ Á ÁH (Fig. 6d) contacts, with a 15.5% contribution to the HS, has a symmetrical distribution of points with the edges at d e + d i = 2.58 Å ( Table 2). The pair of characteristic wings resulting in the fingerprint plot shown in Fig. 6(e), with an 11.1% contribution to the HS, arises from the OÁ Á ÁH/HÁ Á ÁO contacts (Table 2)  View of the three-dimensional Hirshfeld surface of the title compound plotted over the electrostatic potential energy in the range À0.0500 to 0.0500 a.u. using the STO-3G 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 5
Hirshfeld surface of the title compound plotted over shape-index. Table 2 Selected interatomic distances (Å ). (2) points with the tip at d e = d i = 13.50 Å . Finally, the tiny characteristic wings resulting in the fingerprint plots shown in Fig. 6g 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, HÁ Á ÁN/NÁ 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 the standard B3LYP functional and 6-311G(d,p) basis-set calculations (Becke, 1993) as implemented in GAUSSIAN09 (Frisch et al., 2009). The theoretical and experimental results are in good agreement ( Table 3). 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 clarify the inevitable charge exchange collaboration inside the studied material, and electronegativity (), hardness (), potential (), electrophilicity (!) and softness () are all recorded in Table 4. The significance of and is to evaluate both the reactivity and stability. The electron transition from the HOMO to the LUMO energy level is shown in Fig. 8

Refinement
The experimental details including the crystal data, data collection and refinement are summarized in Table 5. H atoms were located in a difference Fourier map and refined freely. The energy band gap of the title compound.  program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg & Putz, 2012); software used to prepare material for publication: SHELXTL (Bruker, 2016). All H-atom parameters refined w = 1/[σ 2 (F o 2 ) + (0.0539P) 2 + 0.2048P]

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.