Crystal structure and Hirshfeld surface analysis of (E)-2-{[(2-iodophenyl)imino]methyl}-6-methylphenol

In the crystal, molecules are linked by C—H⋯π interactions, resulting in the formation of sheets along the a-axis direction. Within the sheets, very weak π–π stacking interactions occur. The Hirshfeld surface analysis and fingerprint plots reveal that the crystal structure is dominated by H⋯H (37.1%) and C⋯H (30.1%) contacts.


Chemical context
Imines derived from o-hydroxy aromatic carbonyls are of interest because of their ability to form an asymmetric intramolecular hydrogen bond between the oxygen atom of the hydroxyl group and the nitrogen atom of the imine moiety (Dominiak et al., 2003). This ability has a decisive impact on the biological and thermo-or photochromic properties of ohydroxy aromatic Schiff bases and makes them very useful compounds in chemistry, biochemistry, medicine, and technology (Vlad et al., 2018;Bouhidel et al., 2018;Faizi et al., 2020a,b). A very important issue is determining the positions of tautomeric equilibria in these compounds and various instrumental research techniques are used to provide insight into the structure of molecules of studied o-hydroxy Schiff bases (Wojciechowski et al., 2003;Faizi et al., 2020c,d).
In the present study, a new Schiff base, (E)-2-{[(2-iodophenyl)imino]methyl}-6-methylphenol, was obtained in crystalline form from the reaction of 2-hydroxy-3-methylbenzaldehyde with 2-iodoaniline. We report here the synthesis and ISSN 2056-9890 the crystal and molecular structures of the title compound, along with the results of a Hirshfeld surface analysis.

Structural commentary
Depending on the tautomers, two types of intramolecular hydrogen bonds are observed in Schiff bases: O-HÁ Á ÁN in enol-imine and N-HÁ Á ÁO in keto-amine tautomers. Most of these compounds are non-planar. The title compound, (I), is a Schiff base derivative from 2-hydroxy-3-methylbenzaldehyde, which crystallizes in the phenol-imine tautomeric form with an E configurationfor the imine functionality. The asymmetric unit of (I) contains one molecule (Fig. 1). The molecule is nonplanar with the 2-iodophenyl and benzene rings twisted with respect to each other at a dihedral angle of 31.38 (2) . The hydroxyl H atom is involved in a strong intramolecular O-HÁ Á ÁN hydrogen bond, forming an S(6) ring motif, which stabilizes the molecular structure and induces the Schiff base atoms (N1, C7) to be coplanar with the methylphenol moiety. Of this planar unit (r.m.s deviation = 0.0274 Å ), atoms O1 and N1 show the largest deviations from planarity in positive and negative directions [O1 = 0.035 (4) Å and N1 = À0.060 (4) Å ]. The C7-N1 and C13-O1 bonds of the title compound are the most important indicators of the tautomeric type. The C13-O1 bond is of double-bond character for the ketoamine tautomer, whereas this bond displays single-bond character in the enol-imine tautomer. In addition, the C7-N1 bond is also a double bond in the enol-imine tautomer and a single bond length in the keto-amine tautomer. In the title compound, the enol-imine form is favored over the ketoamine form, as indicated by the C13-O1 [1.352 (6) Å ] and C7-N1 [1.286 (8) Å ] bonds, whose lengths indicate a high degree of single-bond and double-bond character, respectively. The shortest C-C distance (C3-C4) is 1.344 (11) Å in the C1-C6 ring with the weighted average ring bond distance being 1.376 (11) Å for this ring.

Supramolecular features
In the crystal structure, the molecules are connected into sheets extending along the a-axis direction by C2-H2Á Á ÁCg2 i interactions (Table 1; Fig. 2). Within the sheets, very weakstacking interactions are observed with a centroid-to-centroid distance Cg1Á Á ÁCg2 ii of 4.093 (2) Å (Fig. 3), where Cg1 and Cg2 are the centroids of the C1-C6 and C8-C13 rings, respectively.

Hirshfeld surface analysis
A Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) was carried out using CrystalExplorer17.5 (Turner et al., 2017). The Hirshfeld surfaces and the associated two-dimensional fingerprint plots were used to quantify the various intermolecular interactions in the structure. The Hirshfeld surfaces (d norm and shape-index) of the title compound are illustrated in Fig Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view of the crystal packing of the title compound in a view parallel to the bc plane. C-HÁ Á Á(ring) interactions are indicated by dashed lines.

Figure 3
A view of the crystal packing of the title compound along the a axis.

Figure 1
The molecular structure of the title compound, with atom labelling. The intramolecular N-HÁ Á ÁO hydrogen bond (Table 1) is indicated by a dashed line. Displacement ellipsoids are drawn at the 40% probability level.
hence most of the interactions are weak non-covalent interactions. The diffuse white areas identified in Fig. 4a and red areas on phenyl rings mapped with shape-index ( Fig. 4b) correspond to the HÁ Á Á contacts resulting from hydrogen bond C-HÁ Á Á(ring) ( Table 1) andstacking interactions.
The major intermolecular interactions in the crystal structure are HÁ Á ÁH, HÁ Á ÁC and HÁ Á ÁI interactions, which make individual contributions of 37.1%, 30.1% and 18%, respectively. The fingerprint plots are shown in Fig. 5. There are also OÁ Á ÁH (6.4%), NÁ Á ÁH (3.6%) and CÁ Á ÁC (23.3%) contacts. The Hirshfeld surface analysis confirms the importance of H-atom contacts in establishing the packing. The large number of HÁ Á ÁH and CÁ Á ÁH interactions suggest that van der Waals interactions play the major role in the crystal packing.

Synthesis and crystallization
The title compound was prepared by refluxing mixed solutions of 2-hydroxy-3-methylbenzaldehyde ( Two-dimensional fingerprint plots for the title compound, with a d norm view and the relative contribution of the atom pairs to the Hirshfeld surface.

Figure 4
The Hirshfeld surfaces of the title compound mapped over (a) d norm and (b) shape-index.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound H atoms were placed according to the difference-Fourier map and refined using a riding model: C-H = 0.93-0.96 Å with U iso (H) = 1.5U eq (Cmethyl) and 1.2U eq (C) for other H atoms. Hydroxyl H atoms were placed according to a difference-Fourier map and were freely refined. The crystal studied was refined as a twocomponent inversion twin. This reflection file contains the non-overlapping reflections of the two twin components as well as the overlapping reflections. The BASF parameter for this two-component twin refined to À0.03242 (8). SHELXL2017/1 (Sheldrick, 2015b); molecular graphics: PLATON (Spek, 2020); software used to prepare material for publication: WinGX (Farrugia, 2012).

(E)-2-{[(2-Iodophenyl)imino]methyl}-6-methylphenol
Crystal data 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. Refinement. Refined as a two-component inversion twin.