Synthesis, crystallographic analysis and Hirshfeld surface analysis of 4-bromo-2-{[2-(5-bromo-2-nitrophenyl)hydrazin-1-ylidene]methyl}-5-fluorophenol

The title compound is nearly planar with a dihedral angle of 10.6 (4)° between the two benzene rings.


Chemical context
Hydrazones, the most important derivatives of carboxaldehyde, are widely used both in organic synthesis and in industrial work because of their reaction abilities, such as ring closing, oxidation-reduction, replacement reactions and coupling (Ö ztü rk et al., 2003). They are generally considered to be useful starting materials for the production of pharmaceuticals, pesticides, textile dyestuffs as well as compounds that serve as stabilizers and inhibitors in photography (Kaban & Ocal, 1993). In addition, they exhibit a wide range of applications in the fields of biology, optics, catalysis and analytical chemistry. Their broad spectrum of biological activities includes antimicrobial, antifungal, antiviral, antitumor, anti-HIV, anti-inflammatory, antineoplastic and analgesic activities (Sudheer et al., 2015;Soujanya & Rajitha, 2017). Hydrazone-based molecular switches, metalloassemblies and sensors have also been developed (Sudheer et al., 2015). Unlike oximes (Sliva et al., 1997;Penkova et al., 2010;Pavlishchuk et al., 2010), hydrazones are mostly obtained as a mixture of E and Z isomers and both isomers are generally weak acids (Mori et al., 2015). Tautomerism between the isomers might also occur in the case of the hydrazone and azo forms (Aydemir & Kaban, 2018). In this study, the structure of the newly synthesized compound has been evaluated by spectroscopic techniques. In view of this, in order to obtain information about the stereochemistry of the molecule and to confirm the assigned structure, X-ray analysis of the title compound was undertaken.

Hirshfeld surface analysis
A Hirshfeld surface analysis was performed to quantify the nature of the intermolecular interactions. The Hirshfeld surfaces were generated using CrystalExplorer17.5 (Turner et al., 2017) using a standard (high) surface resolution. Fig. 3 shows the Hirshfeld surfaces mapped over d norm in the range À0.2247 (red) to 1.3787 (blue) a.u. If the value of d norm is negative, the intermolecular contacts are shorter than the van der Waals radius; these are shown as red regions. A positive value of d norm , shown in blue, indicates that the intermolecular contacts are longer than the van der Waals radius (Ş en et al., 2017). The red regions on the d norm surface correspond to C-HÁ Á ÁO hydrogen-bonding interactions, which comprise 20.2% of the total Hirshfeld surfaces.
The two-dimensional fingerprint (FP) plots are used to analyse significant differences between the intermolecular interaction patterns (Gumus et al., 2018;Kansız & Dege, 2018;Kansiz et al., 2018). Fig. 4 represents the FP plot for the sum of the contacts contributing to the Hirshfeld surface displayed in normal mode. In Fig. 5 distinct spikes indicate different interactions between two adjacent molecules in the crystal structure. The contribution from the BrÁ Á ÁH/HÁ Á ÁBr contacts make the largest (21.7%) to the Hirshfeld surface (Fig. 5b). The 20.2% contribution from the O-HÁ Á ÁO hydrogen bond is seen as a pair of sharp spikes at d e + d i = 2.3 Å ) in Fig. 5a. The distribution of positive and negative potential over the Hirshfeld surface is represented in Fig. 6 (positive electrostatic potential shown in blue region and negative electrostatic potential in red).

Figure 2
The view of the crystal packing of the title compound.
research communications Figure 4 Fingerprint plot of the title compound showing all interactions.

Figure 6
A view of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potential.

Figure 3
Views of the Hirshfeld surface of the title compound mapped over d norm .

Synthesis and crystallization
5-Bromo-4-fluoro-2-hydroxybenzaldehyde (0.5 mmol) was dissolved in hot absolute ethanol (10 mL) and an equimolar amount of 5-bromo-2-nitrophenylhydrazine, dissolved in a minimum volume of absolute ethanol, was slowly added. The product appeared in the first minute. The reaction mixture was refluxed for an additional hour to complete the condensation and then allowed to cool in room temperature. The separated solid was then filtered and washed with ethanol and diethyl ether. The crude product was recrystallized from toluene as pink needle-shaped crystals, 96% yield, m.p. 569-570 K (dec.). The reaction scheme is shown in Fig. 7

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound hydrogen atoms were positioned geometrically and refined using a riding model: C-H = 0.93-0.97 Å with U iso (H) = 1.2U eq (C) Figure 7 The synthesis of the title compound.