Crystal structure and Hirshfeld surface analysis of (Z)-2-{[(2,4-dimethylphenyl)imino]methyl}-4-methylphenol

The title Schiff base exists in the enol–imine tautomeric form and adopts a Z configuration. In the crystal, the molecules are linked by weak C—H⋯π hydrogen bonds and very weak π–π stacking interactions.

The title compound, C 16 H 17 NO, is a Schiff base that exists in the enol-imine tautomeric form and adopts a Z configuration. The molecule is non-planar, with the twisted rings making a dihedral angle of 39.92 (4) . The intramolecular O-HÁ Á ÁN hydrogen bond forms an S(6) ring motif. In the crystal, molecules are linked by C-HÁ Á Á interactions and very weakstacking interactions also help to consolidate the crystal packing. A Hirshfeld surface analysis was performed to investigate the contributions of different intermolecular contacts within the supramolecular structure. The major contributions are from HÁ Á ÁH (65%), CÁ Á ÁH (19.2%) and OÁ Á ÁH (6.6%) interactions.

Chemical context
Schiff bases are well-known organic compounds widely used in many areas. These compounds can be easily synthesized by condensation of a primary aliphatic or aromatic amine with an aldehyde or ketone in different solvent media and they can easily be purified, since the amount of by-products is negligible (Tanak et al., 2020). Schiff bases are in general more stable than the compounds from which they are synthesized (Wadher et al., 2009). Nowadays, the possibility of molecular design is an important key for many research areas such as medicine or agriculture. In this respect, Schiff base formation provides an easy way to design new compounds, and biologically or chemically active compounds can be obtained using this method. As the structures of Schiff bases are generally similar to those of biological molecules, Schiff bases are valuable for understanding biological phenomena. As a result, Schiff bases are used in many studies. Various types of aldehydes or ketones have been used for their synthesis, but 2-hydroxybenzaldehyde and its derivatives are used especially often (Jeewoth et al., 2000;Mazhar et al., 2020). The basis of such preference is the tautomerism and stability provided by the hydroxyl group in conjunction with the imine group. Schiff bases with intramolecular hydrogen bonds can exhibit photochromic and thermochromic properties (Elerman et al., 2002). Schiff bases obtained from 2-hydroxybenzaldehyde and its derivatives can also form complexes with various metal ions. The title compound is a Schiff base prepared from 2-hydroxy-5-methylbenzaldehyde.

Structural commentary
The title compound crystallizes in the phenol-imine tautomeric form with an Z configuration with respect to the imine bond. The asymmetric unit contains one molecule (Fig. 1), which is non-planar, two aromatic rings being twisted with respect to each other, subtending a dihedral angle of 39.92 (4) . The hydroxy and imine groups are involved in a strong intramolecular O1-H1Á Á ÁN1 hydrogen bond forming an S(6) ring motif. The C1-O1 [1.353 (2) Å ] and C7-N1 [1.282 (2) Å ] bond distances indicate their single-and doublebond characters, respectively, being consistent with the phenol-imine tautomeric form.
Cg2 is the centroid of the C9-C14 ring.

Figure 2
A view of the crystal packing of the title compound. The C16-H16AÁ Á ÁCg2 interactions are denoted as dashed lines and as a red spot on the d e surface.

Figure 1
The molecular structure of the title compound, with atom labelling.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The O-bound H atom was located in a difference-Fourier map and refined with O-H = 0.82 Å , and with U iso (H) = 1.5U eq (O). The C-bound H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 and U iso (H) = 1.2U eq (C) for sp 2 -hybridized C atoms and with C-H = 0.96 Å and U iso (H) = 1.5U eq (C) for methyl groups.

Figure 5
The scheme of synthesis of the title compound.