Crystal structure and Hirshfeld surface analysis of 2-{[(4-iodophenyl)imino]methyl}-4-nitrophenol

In the title Schiff base compound, C13H9IN2O3, the hydroxy group forms a intramolecular hydrogen bond to the imine N atom and generates an S(6) ring motif. The 4-iodobenzene ring is inclined to the phenol ring by 39.1 (2)°. The configuration about the C=N bonds is E. The crystal structure features C—H⋯O hydrogen-bonding interactions.


Chemical context
Over the past 25 years, extensive research has been directed towards the synthesis and use of Schiff base compounds in organic and inorganic chemistry as they have important medicinal and pharmaceutical applications. These compounds exhibit biological activities, including antibacterial, antifungal, anticancer and herbicidal properties (Desai et al., 2001;Singh & Dash, 1988;Karia & Parsania, 1999). They may also show useful photochromic properties, leading to applications in various fields such as the measurement and control of radiation intensities in imaging systems and optical computers, electronics, optoelectronics and photonics (Iwan et al., 2007). Schiff bases derived from 2-hydroxy-5-nitrobenzaldehyde are widely used either as materials or as intermediates in explosives, dyestuffs, pesticides and organic synthesis (Yan et al., 2006). Intramolecular hydrogen-atom transfer (tautomerism) from the o-hydroxy group to the imine-N atom is of prime importance with respect to the solvato-, thermo-and photochromic properties of o-hydroxy Schiff bases (Filarowski, 2005;Hadjoudis & Mavridis 2004). Such proton-exchanging materials can be utilized for the design of various molecular electronic devices (Alarcó n et al., 1999). The present work is a part of an ongoing structural study of Schiff bases and their utilization in the synthesis of quinoxaline derivatives , fluorescence sensors (Faizi et al., 2016;Mukherjee et al., 2018;Kumar et al., 2017; and non-linear optical properties (Faizi et al., 2020). We report herein the synthesis (from 2-hydroxy-5-nitrobenzaldehyde and 4-iodoaniline) and crystal structure of the title compound (I), along with the findings of a Hirshfeld surface analysis.

Figure 2
A partial packing plot showing the C-HÁ Á ÁO hydrogen-bonded (thick dashed lines) helical chains about the crystallographic 2 1 screw axis parallel to c.

Figure 3
A partial packing plot showing close contacts (dashed lines) between iodine and the phenolic oxygen of glide-related (x + 1 significant intermolecular interactions present in the crystal. The Hirshfeld surface analysis confirms the role of the C-HÁ Á ÁO interactions in the packing arrangement.

Hirshfeld surface analysis
In order to visualize the intermolecular interactions in the crystal packing of (I), a Hirshfeld surface (HS) analysis (Hirshfeld, 1977;Spackman & Jayatilaka, 2009) was carried out using Crystal Explorer 17.5 (Turner et al., 2017). In the HS plotted over d norm (Fig. 4), white surfaces indicate contacts with distances equal to the sum of van der Waals radii, and the red and blue colours indicate distances shorter (i.e., in close contact) or longer than the van der Waals radii sum, respectively (Venkatesan et al., 2016). The two-dimensional finger print plots are depicted in Fig. 5 Ojala et al., 1999), the OH group is absent and the NO 2 group is replaced by a cyano group. In (E)-5-(diethylamino)-2-[(4-iodophenylimino)methyl]phenol (VEFPED; Kaştaş et al., 2012), the NO 2 is replaced by an N,N diethyl group. In N-(3,5-di-tert-butylsalicylidene)-4-iodobenzene; (MILFET; Spangenberg et al., 2007), the NO 2 group is absent but a pair of t Bu groups occupy the 3,5 positions of the salicylidene group. In 2-{[(4-iodophenyl)imino]methyl}-6-methoxyphenol (SEDBIP; Carletta, et al., 2017), the NO 2 group is absent and a methoxy group is ortho to the hydroxyl. Lastly, in N-(2-cyanobenzylidene)-4-iodoaniline (XOXKIF; Ojala et al., 1999) the NO 2 is absent and the OH is replaced by cyano. All these compounds have an E configuration about the C N bond and form the S(6) ring motif.

Synthesis and crystallization
The title compound was synthesized by condensation of 2-hydroxy-5-nitrobenzaldehyde (11.0 mg, 0.066 mmol) and 4-iodoaniline (14.4 mg, 0.066 mmol) in ethanol (15 ml). After the mixture had refluxed for about 15 h, the orange product was washed with ether and dried at room temperature (yield 60%, m.p. 484-486 K). Crystals suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Two-dimensional fingerprint plots of the crystal with the relative contributions of the atom pairs to the Hirshfeld surface along with d norm full.

Figure 4
Hirshfeld surface of the title compound plotted over d norm.

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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )