Synthesis, Crystal Structures Investigations and Hirshfeld Surface Analysis of Novel Molecule 2, 5-Dihydro [2]Benzopyrano [3,4-c] Pyrazole-water (1/4)

Crystal Structure

The molecular structure containing atomic labeling of the asymmetric unit, ‘4(C10 H8 N2 O), H2 O’ is shown in Figure 2 (ORTEP) [9]. The X-ray analyses showed that the asymmetric unit of the compound (1) contains two crystallographically independent molecules A and B along with a half water molecule. The central moieties of this compound are building from fusion of 1H-isochromene ring and a pyrazole ring.

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The geometry of the title molecule is close to their normal geometry [10]. Moreover, there is very little difference between the bond lengths and angles of the title molecule and the structurally related molecule (C20H19N3O4) [11].

In pyrazole moiety, the bond lengths and angles around nitrogen atoms N7=N8 = 1.371(3)Å and N7-N8-C9 = 112.7(2)° in molecule A, and N27=N28 = 1.371(3)Å and N27- N28-C29 = 112.3(2)°are close to that are in related molecule (C20H19N3O4), respectively.

From the pluckering amplitude analysis of all the investigated molecules, the 1H-isochromene rings have distorted chair conformation where maximum deviation from plane of mean deviation are 0.02669(1) for atom C5 and 0.2439(1) for C25 in the molecule A and B, respectively [12]. All other component of ring moieties are individually planar as reflected from the small value of torsion angles. Furthermore, the dihedral angle value suggests that the pyrazole moiety is in plane to benzene moiety in both molecules A and B respectively. The bond lengths and bond angles for non-hydrogen atoms in compound 1 are shown in Table 2.

Analysis of the crystal packing showed that there exist intermolecular hydrogen bonds of O-H…N, N-H…O, N-H…N and C-H…O type, along with π-π and Van der Waal’s forces; which play an important role in crystal structure stabilization. Packing view of molecules within the unit cell is generated using PLATON and viewed down to c-axis are shown in Figure 3. The active H atom H28 of the pyrazole moiety B attached at N28 atom participate with N7 nitrogen atom of molecule A, in formation of N-H…N intermolecular hydrogen bonds [13]. Figure 3 is the wire and frame image shown perpendicular along c direction forming chain like patterns.

Pyrazole rings are closely stacked through π-π interactions. The geometry of these interactions is presented in Tables 3 and 4. CgI represents the center of gravity of the ring (N27/N28/C29/C22/C21) and CgJ represents the center of gravity of the ring (N7/N8/C9/C2/C1). CgI···CgJ represents the distance between the ring centroid; CgI···P represents the perpendicular distance of the centroid of one ring from the plane of the other; α is the dihedral angle between the planes of rings I and J; β is the angle between the normal to the centroid of the ring I and the line joining ring centroids; Δ is the displacement of the centroid of rings J relative to the intersection point of the normal to the centroid of ring I and the least- squares plane of ring J.

Hirshfeld Surface Analysis

The mapping of intermolecular tight interactions in molecular crystals can be studied qualitatively and quantitatively using the Hirshfeld surface analysis. A set of points in 3D space where the contribution of the molecule of interest to the electron density is equal to the contribution of all other molecules make up the Hirshfeld surface that encloses that molecule [12]. Molecular Hirshfeld surfaces are constructed using an electron distribution model where the electron densities of all the spherical atoms are added together [14]. A standard (high) surface resolution was used to create the molecular Hirshfeld surface for the compound 1, and the 3D dnorm surfaces were mapped across a predetermined color scale of -1.2783 a. u. (red) to 1.2612 a. u. (blue). Figure 4(a) shows that a sizable red area on the molecule’s dnorm surface is connected to the brief cyclic hydrogen bond connection between H28 and N7. The shape index was mapped in the -1.0 to 1.0 color space. Figure 4 (b) demonstrates the presence of self-complementary patches for the molecule that exhibits close stacking. The degree of curvature was plotted between -4.0 and 0.4. Small, relatively flat green areas are separated by broad, positive curved dark blue boundaries in Figure 4(c) showing that benzene rings are involved in the π- π sequence.

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Plotting 2D fingerprint graphs involves adding together (di, de) pairs. Each collection’s coloring is determined by the fraction of crystal 1 surface points, ranging from blue (few points) to green (average points) to red (many points). Figure 5 displays the associated 2D fingerprint plots [15] for the crystal 1 Hirshfeld surfaces, which highlight the primary intermolecular interactions and their proportional contribution to the total Hirshfeld surface area. The prominent symmetrical spike in the fingerprint map of crystal 1 emerges owing to O···H/H···O contacts, is attributed to the existence of a strong (C-H...O) hydrogen bond interaction with minimum (di + de)value of 2.80 Å. Table 5 shows that H···H interaction followed by H···C/C···H interaction with 48.6 and 21.7 % respectively making a significant contribution among all common Hirshfeld surfaces, which are reflected in middle and upper half of scattered points in 2D fingerprint plots.