Crystal structure and Hirshfeld surface analysis of (4Z)-1-butyl-4-(2-oxopropylidene)-2,3,4,5-tetrahydro-1H-1,5-benzodiazepin-2-one

The asymmetric unit of the title compound consists of two independent molecules differing slightly in the conformations of the seven-membered rings and the butyl substituents.


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 Explorer17.5 (Turner et al., 2017). In the HS plotted over d norm (Fig. 4), 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 appearing near O1, O2, O3 and hydrogen atoms H18, H19 and H28C indicate their roles as the respective donors and acceptors in the dominant C-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds. The shape-index of the HS is a tool Detail of intermolecular C-HÁ Á ÁO hydrogen bonding (black dashed lines) and C-HÁ Á Á (ring) interactions (green dashed lines) viewed along the a-axis direction.

Figure 1
The asymmetric unit with the labelling scheme and 50% probability ellipsoids. N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds are indicated by blue and black dashed lines, respectively.

Figure 3
Packing viewed along the a-axis direction with intermolecular interactions depicted as in Fig. 2. for visualizingstacking interactions 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.
The overall two-dimensional fingerprint plot, Fig. 6a, 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, OÁ Á ÁC/CÁ Á ÁO, NÁ Á ÁC/CÁ Á ÁN and CÁ Á ÁC contacts (McKinnon et al., 2007) are illustrated in Fig. 6b-h, respectively, together with their relative contributions to the Hirshfeld surface. The most important interaction is HÁ Á ÁH contributing 65.5% to the overall crystal packing, which is reflected in Fig. 6b as widely scattered points of high density due to the large hydrogen-atom content of the molecule. The wide peak in the centre at d e = d i = 1.16 Å in Fig. 6b is due to the short interatomic HÁ Á ÁH contacts (Table 2). In the presence of weak C-HÁ Á Á interactions (Table 1) in the crystal, the pair of characteristic wings resulting in the fingerprint plot delineated into HÁ Á ÁC/CÁ Á ÁH contacts, Fig. 6c, the 16.0% contribution to the HS is viewed as pair of spikes with the tips at d e + d i $ 2.73 Å . The HÁ Á ÁO/OÁ Á ÁH contacts in the structure, with 15.8% contribution to the HS, have a symmetrical distribution of points, Fig. 6d, with the tips at d e + d i $2.24 Å arising from the short intra-and/or interatomic C-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonding (Table 1) as well as from the HÁ Á ÁO/OÁ Á ÁH contacts (  View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.2745 to 1.3634 a.u.

D-HÁ
distribution of points, with a pair of wings appearing at d e = d i = 2.67 Å . The Hirshfeld surface representations for d norm are shown for the HÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH and HÁ Á ÁO/OÁ Á ÁH interactions in 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).

Synthesis and crystallization
To a solution of (Z)-4-(2-oxopropylidene)-4,5-dihydro-1Hbenzo[b][1,5]diazepin-2(3H)-one (2.38 mmol) in 15 ml of dichloromethane were added 1.5 eq of 1-bromobutane, (3.57 mmol) of potassium hydroxide dissolved in water and 0.23 mmol of tetra-n-butyl ammonium bromide (BTBA). The mixture was kept under magnetic stirring at room temperature for 48 h. A little water was added and then the organic phase was extracted. The mixture obtained was chromatographed on a column of silica gel (eluent hexane/ethyl acetate 8/2) to give three products. The title compound was isolated as the major product in a yield of 77%.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms attached to C28 did not give a satisfactory geometry so they were positioned geometrically with C-H = 0.98 Å , and refined as riding with U iso (H) = 1.5U eq (C). The remaining H atoms were located in a difference-Fourier map and were freely refined. The crystal studied was twinned.

Figure 6
The full two-dimensional fingerprint plots for the title compound SHELXTL (Sheldrick, 2008).

Special details
Experimental. The diffraction data were obtained from 3 sets of 400 frames, each of width 0.5° in ω, colllected at φ = 0.00, 90.00 and 180.00° and 2 sets of 800 frames, each of width 0.45° in φ, collected at ω = -30.00 and 210.00°. The scan time was 20 sec/frame. Analysis of 641 reflections having I/σ(I) > 13 and chosen from the full data set with CELL_NOW (Sheldrick, 2008) showed the crystal to belong to the triclinic system and to be twinned by a 180° rotation about the reciprocal axis [111]. The raw data were processed using the multi-component version of SAINT under control of the two-component orientation file generated by CELL_NOW. 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. Refined as a 2-component twin. Individual refinement of the H-atoms attached to C28 did not give a satisfactory geometry so these were included as riding contributions in idealized positions.