Crystal structures of two dis-symmetric di-Schiff base compounds: 2-({(E)-2-[(E)-2,6-dichlorobenzylidene]hydrazin-1-ylidene}methyl)-6-methoxyphenol and 4-bromo-2-({(E)-2-[(E)-2,6-dichlorobenzylidene]hydrazin-1-ylidene}methyl)phenol

An E-configuration about the imine bond is found in both the title molecules, which differ in their central C—N—N—C torsion angles. The main feature of the molecular packing in both crystals is the formation of supramolecular chains: the linear chains in (I) are consolidated by methoxy-C—H⋯O(methoxy) and chlorobenzene-C—Cl⋯π(chlorobenzene) interactions while the zigzag chains in (II) are sustained by Br⋯O secondary bonding interactions.


Supramolecular features
The two prominent directional interactions in the molecular packing of (I) are of the type C-HÁ Á ÁO and C-ClÁ Á Á, Table 2. Thus, methoxy-C-HÁ Á ÁO(methoxy) and chlorobenzene-C-ClÁ Á Á(chlorobenzene) contacts serve to link molecules into supramolecular chain aligned along the a-axis direction, Fig. 2(a). The linear chains thus formed assemble in the crystal without directional contacts between them, Fig. 2(b). Supramolecular chains along the a axis are also noted in the packing of (II), Fig. 3(a). In this instance, the contacts between molecules are of the type BrÁ Á ÁO, i.e. the Br1Á Á ÁO1 separation is 3.132 (4) Å for symmetry operation 1 2 + x, 3 À y, z. With the first such interaction in a crystal being reported in 1954, i.e. in the crystal of Br 2 ÁO(CH 2 CH 2 ) 2 O (Hassel & Hvoslef, 1954), these well-described secondary bonding interactions (Alcock, 1972), are termed halogen-bonding interactions in the current parlance (Tiekink, 2017). In (II), the BrÁ Á ÁO interactions assemble molecules into zigzag chains as these are propagated by glide symmetry. Globally, the supramolecular chains stack along the b axis to form layers and the layers stack along the c axis in an . . . ABAB . . . fashion, Fig. 3(b), but there are no directional interactions between the chains.

Hirshfeld surface analysis
The Hirshfeld surfaces for (I) and (II) were calculated employing the Crystal Explorer 17 program (Turner et al., 2017) following recently published protocols (Tan et al., 2019). The results describe the influence of non-bonded interactions upon the molecular packing in the crystals of (I) and (II), especially in the absence of directional interactions between the chains.
On the Hirshfeld surfaces mapped over d norm , the presence of the bright-red spots near the methoxy-O2 and H15B atoms for (I) in Fig. 4(a),(b) and those near the Br1 and hydroxyl-O1 atoms in Fig. 5(a) for (II), are indicative of dominant intermolecular C-HÁ Á ÁO and BrÁ Á ÁO contacts in their respective crystal structures. The faint-red spots viewed near the imine-N2 and H8 atoms for (I), and near the Cl2 and H7 atoms for (II) in Fig. 4(a),(b) and 5(b), respectively, indicate the influence of short interatomic contacts (Table 4) Table 2, is illustrated through a blue bump and a orange concave region in the Hirshfeld surface mapped with the shape-index property in Fig. 4(c).
The overall two-dimensional fingerprint plots for (I), Fig. 7(a), and (II), Fig.7(f), and those delineated into HÁ Á ÁH, OÁ Á ÁH/HÁ Á ÁO, CÁ Á ÁH/HÁ Á ÁC and CÁ Á ÁC contacts for (I) are illustrated in Fig. 7(b)-(e), respectively, and the equivalent plots for (II) are found in Fig. 7(g)-(j). The percentage contributions from the different interatomic contacts to the Hirshfeld surfaces of (I) and (II) are quantitatively summarized in Table 5. For (I), the short interatomic HÁ Á ÁH contact between the methoxy-H15A and dichlorobenzene-H13 atoms, Table 4, is evident as a pair of almost fused peaks at d e + d i $2.3 Å in Fig.7(b). In (II), comparable interactions are at interatomic distances farther than the sum of their van der Waals radii. The decrease in the percentage contribution from HÁ Á ÁH contacts to the Hirshfeld surface of (II) compared to (I),    Views of the Hirshfeld surface for (II) mapped over d norm in the range À0.016 to 1.528 arbitrary units. Table 4 Summary of short interatomic contacts (Å ) for (I) and (II) a .

Contact
Distance Symmetry operation to the methoxy group in (I), and its participation in a number of surface contacts, most notably BrÁ Á ÁH/HÁ Á ÁBr contacts (13.7%).

Figure 6
A view of the Hirshfeld surface mapped over the electrostatic potential (the red and blue regions represent negative and positive electrostatic potentials, respectively): (a) for (I) in the range À0.071 to +0.038 atomic units and (b) for (II) in the range À0.063 to +0.040 atomic units.  The presence of C-HÁ Á ÁO contacts in the crystal of (I) is characterized as the pair of forceps-like tips at d e + d i $2.5 Å in the fingerprint plot delineated into OÁ Á ÁH/HÁ Á ÁO contacts, Fig. 7(c), with the points related to other short interatomic OÁ Á ÁH contacts merged within. The comparatively small contribution from these contacts in (II), Table 5, show the points to be at distances greater than sum of their van der Waals radii in Fig. 7(h). In the fingerprint plot delineated into CÁ Á ÁH/HÁ Á ÁC contacts for both (I) and (II), Fig. 7(d) and (i), the characteristic wings are observed but with different shapes. Their relatively long interatomic distances are consistent with the absence of intermolecular C-HÁ Á Á or short CÁ Á ÁH contacts in the crystals. The absence of aromaticstacking is also evident from the fingerprint plots delineated into CÁ Á ÁC contacts, Figs. 7(e) and (j), although significant percentage contributions from these contacts are noted, Table 5. In addition to the above, some specific contacts occur in the crystals of (I) and (II).
The pair of forceps-like tips at d e + d i $2.5 Å in the fingerprint plot delineated into NÁ Á ÁH/HÁ Á ÁN contacts for (I) in Fig. 7(k) indicate the short interatomic NÁ Á ÁH contact involving the imine-N2 and H12 atoms, Table 4, formed within the supramolecular chain along a axis Fig. 2(a). Also, in the fingerprint plot delineated into CÁ Á ÁCl/ClÁ Á ÁC contacts for (I), Fig. 7(l), the C-ClÁ Á Á contacts are highlighted as the pattern of blue points at separations as close as d e = d i = 1.85 Å . In the case of (II), in the fingerprint plot delineated into ClÁ Á ÁH/ HÁ Á ÁCl contacts, Fig. 7(m), the short interatomic contact involving the Cl2 and imine-H7 atoms is apparent as the pair of spikes with their tips at d e + d i $2.7 Å . Finally, the presence of interatomic BrÁ Á ÁO interactions along the a axis in the crystal is reflected in the pair of thin spikes at d e + d i $3.2 Å in Fig. 7(n). The comparatively greater percentage contribution from interatomic contacts such as CÁ Á ÁO/OÁ Á ÁC and ClÁ Á ÁCl to the surface of (I) and BrÁ Á ÁH/HÁ Á ÁBr and CÁ Á ÁN/NÁ Á ÁC to that of (II) as well as smaller contributions from other contacts as summarized in Table 5, show negligible effect on the respective molecular packing due to the interatomic separations being equal to or exceeding the respective sums of the van der Waals radii.

Energy frameworks
The pairwise interaction energies between the molecules in the crystals of (I) and (II) were calculated by summing up four energy components, these being the electrostatic (E ele ), polarization (E pol ), dispersion (E dis ) and exchange-repulsion (E rep ) terms (Turner et al., 2017). The energies were obtained using the wavefunctions calculated at the B3LYP/6-31 G(d,p) and HF/STO-3 G levels theory for (I) and (II), respectively. The individual energy components as well as the total interaction energy were calculated relative to a reference molecule. The nature and strength of the energies for the key identified intermolecular interactions are summarized in Table 6.
It is apparent from the interaction energies calculated for (I) that the dispersion component, E dis , makes the major contribution to the C-ClÁ Á Á and NÁ Á ÁH contacts and these are dominant in the molecular packing. By contrast, the C-HÁ Á ÁO interaction has nearly equal contributions from the electrostatic component, E ele , and E dis . The small value of the interaction energy corresponding to the short HÁ Á ÁH contact arises primarily from E dis . The intermolecular BrÁ Á ÁO and ClÁ Á ÁH contacts instrumental in the crystal of (II) have small interaction energy values dominated by E dis . Fig. 8 represents graphically the magnitudes of intermolecular energies in the form of energy frameworks, which provide a view of the supramolecular architecture of crystals  Table 6 Summary of interaction energies (kJ mol À1 ) calculated for (I) and (II).

Figure 8
The through cylinders joining centroids of molecular pairs by using red, green and blue colour codes for the components E ele , E disp and E tot , respectively. The radius of the cylinder is proportional to the magnitude of the interaction energies which are adjusted to same scale factor of 50 with a cut-off value of 3 kJ mol À1 within 4 Â 4 Â 4 unit cells. The appearance of the energy frameworks clearly reflect the foregoing discussion, namely the clear dominance of the E dis terms, especially for (II).

Database survey
In a recent contribution describing the structure of the analogue of (I) where the methoxy substituent is absent (Manawar et al., 2019b), i.e. (III), it was noted that crystal structure determinations of molecules with the 2-OH-C 6 -C(H)N-NC(H)-C 6 fragment number fewer than ten, and that there is some conformational flexibility in these molecules. This observation is borne out in the present study where there is a disparity of over 25 in the central C7-N1-N2-C8 torsion angle, i.e. À151.0 (3) and 177.8 (6) for (I) and (II), respectively. These values compare with the equivalent angle of À172.7 (2) in (III). An overlay diagram for (I)-(III) is shown in Fig. 9: here, the different conformations for (I), cf.

Synthesis and crystallization
The title compounds were synthesized and characterized as per the procedures reported in the literature (Manawar et al., 2019a). The crystals of (I) and (II) in the form of yellow blocks suitable for the structural study reported here were grown by slow evaporation of their chloroform solutions. Two overlay diagrams of (I)-(III), represented by red, green and blue images, respectively. The molecules have been overlapped so the O1, N1 and C1 atoms are coincident.  (Parsons et al., 2013).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 7

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.