Crystal structure and Hirshfeld surface analysis of 4-{[(anthracen-9-yl)methyl]amino}benzoic acid dimethylformamide monosolvate

In the crystal structure of the title compound intermolecular hydrogen-bonding interactions and weak C—H⋯π interactions between the constituents lead to the formation of a three-dimensional network. Hirshfeld surface analysis revealed that H⋯H interactions dominate the crystal packing.


Chemical context
Schiff bases belong to a class of organic compounds that are formed by the condensation reaction of a carbonyl carbon with an aliphatic/aromatic amine, resulting in the formation of a characteristic imine bond (-HC N-). Many Schiff bases exhibit activities of biological and pharmaceutical significance. Moreover, Schiff bases are actively used as organic linkers for building metal complexes with interesting properties.

Supramolecular features
Classical hydrogen-bonding interactions between the carboxylic OH group (O1) and the solvent O atom (O3) as well as between the amine functionality (N1) and the O atom of the carboxylic group (O2) lead to the formation of supramolecular layers extending parallel to (101) (Fig. 2, Table 1). C-HÁ Á Á interactions involving the phenyl C-H groups of PABA as donor groups and the system of the anthracene moiety link adjacent layers into a three-dimensional network (Fig. 3, Table 1).

Hirshfeld Surface Analysis
Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) and the associated two-dimensional fingerprint plots (McKinnon et al., 2007) were performed with CrystalExplorer (Turner et al., 2017). The Hirshfeld surfaces are colour-mapped with the normalized contact distance, d norm , varying from red (distances shorter than the sum of the van der Waals radii) through white to blue (distances longer than the sum of the van der Waals radii). The positions of the O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds between the molecules are indicated by the red regions on the Hirshfeld surface (Fig. 4).
The two-dimensional fingerprint plot ( The molecular structures of the components in the title compound. Displacement ellipsoids are drawn at the 50% probability level.   Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
The crystal packing showing C-HÁ Á Á interactions between the layers, building up a three-dimensional network.

Figure 4
Hirshfeld surface of the two molecules in the title compound mapped over d norm , in the colour range À0. 461 to 1.471 a.u.. 47.9%, 34.2%, 0.6% and 13.7%, respectively, to the overall surface.

Synthesis and crystallization
The Schiff base was synthesized and subsequently reduced by a reported procedure (Ahmed et al., 2020). To this reduced ligand (0.15 mmol), ethanol and dimethylformamide were added in an equal volume ratio, and the mixture was heated under reflux for 3-4 h at 353 K. The solution was then allowed to cool to room temperature, filtered and kept for slow evaporation. After 10 to 12 d, small colourless block-like crystals began to grow that were dried and characterized by single crystal X-ray diffraction.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms bound to N or O atoms were located in a difference-Fourier map and were freely refined, while the C-bound hydrogen atoms were included in calculated positions and allowed to ride on their parent C atom: C-H = 0.93-0.97 Å with U iso (H) = 1.2U eq (C).