Synthesis, crystal structure and Hirshfeld surface analysis of N-(6-acetyl-1-nitronaphthalen-2-yl)acetamide

The title compound, C14H12N2O4, obtained from 2-acetyl-6-aminonaphthalene through two-step reactions of acetylation and nitration, is a Prodane fluorescent dye. In the crystal, the molecules are assembled into two-dimensional sheet-like structures by intermolecular N—H⋯O hydrogen bonding and π–π stacking interactions. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from O⋯H/H⋯O (43.7%), H⋯H (31.0%), and C⋯H/H⋯C (8.5%) contacts.

The title compound, C 14 H 12 N 2 O 4 , was obtained from 2-acetyl-6-aminonaphthalene through two-step reactions of acetylation and nitration.The molecule comprises the naphthalene ring system consisting of functional systems bearing a acetyl group (C-2), a nitro group (C-5), and an acetylamino group (C-6).In the crystal, the molecules are assembled into two-dimensional sheetlike structures by intermolecular N-H� � �O and C-H� � �O hydrogen-bonding interactions.Hirshfeld surface analysis illustrates that the most important contributions to the crystal packing are from O� � �H/H� � �O (43.7%),H� � �H (31.0%), and C� � �H/H� � �C (8.5%) contacts.

Chemical context
Organic small molecules with naphthalene ring systems are attractive photonic materials due to their high photoluminescence quantum efficiency, color tunability, and sizedependent optical properties (Wang et al., 2012;Yao et al., 2013).Modifying the organic molecular structure can tune the intermolecular hydrogen-bonding and �-� stacking interactions, which influence their packing mode during selfassembly and determine the final aggregated structures.The molecular stacking patterns in crystals can affect asymmetric light propagation (Yagai et al., 2012;Zou et al., 2018;Zhang et al., 2018).
The title compound (I), N-(6-acetyl-1-nitronaphthalen-2yl)acetamide, obtained from 2-acetyl-6-aminonaphthalene through two-step reactions of acetylation and nitration, is a Prodane fluorescent dye with red fluorescence and a large Stoke shift (Xu et al., 2017).The stacking of naphthalene compounds into crystals depends on intermolecular hydrogen bonds and �-� stacking interactions.The nitro group and the acetylamino group of the naphthalene ring system will affect intermolecular interactions, making it possible to change the one-or two-dimensional stacking arrangement, which in turn

Structural commentary
The molecular structure of the title compound (I) is shown in Fig. 1.The molecules are semi-rigid and almost fully coplanar, except for the nitro oxygen atoms and methyl hydrogen atoms.Notably, compound (I) has a primary amine group on the naphthalene core, while the reactant has a secondary amine at the same position.It may have more steric repulsion with neighboring molecules compared to the reactant when assembled into 2D structures.Self-assembly of naphthalene framework organic molecules through �-� stacking forms 3D sheet-like structures with uniform dimensions.
In compound (I), the nitro group and acetylamino group are adjacent, located at positions C-5 and C-6, respectively, and the acetyl group is located at the 2-position of the naphthalene ring system.The angle between the two oxygen atoms on the nitro group located at positions C-5 is 123.93 (18) � , and the torsion angles C6-C5-N1-O3 and C10-C5-N1-O3 are À 90.34 (15) and 89.66 (15) � , respectively.The angles of the acetyl group at the 2-position, O1-C11-C2 and O1-C11-C12, are 120.13(18) and 120.52 (18) � , respectively.In addition, the dihedral angle between the nitro group and the plane through the naphthalene ring system is 89.66 (15) � .

Supramolecular features
In the crystal, a unit cell contains four molecules, which exhibit a centrosymmetric arrangement (Fig. 2), and hydrogen bonding and �-� stacking interactions were responsible for the formation of the crystal structures with distinct morphologies.
The growth pattern for the title compound (I) is a 1D wirelike structure and hydrogen bonding advances the growth along the a-axis direction.The molecules are linked via N2-H2� � �O1 hydrogen bonds, generating 2D layers propagating along the [010] axis direction (Table 1).Without hydrogen-bonding and other strong interactions between molecules in adjacent layers, �-� stacking interactions, with centroid-centroid distcances of 3.67 A ˚, are the predominant driving force during self-assembly, which facilitates the crystal of the title compound growth along the [010] direction, forming a 3D structure (Meva et al., 2012;Nguyen et al., 2004).Weak C4-H4� � �O2 contacts are also observed.

Hirshfeld Surface analysis
A Hirshfeld surface analysis was performed and the associated fingerprint plots, which provide a 2D view of the intermolecular interactions within molecular crystals, were gener- The molecular structure of the title compound (I) with the atomic numbering scheme.Displacement ellipsoids are depicted at the 50% probability level.

Figure 3
Front view of the three-dimensional Hirshfeld surface of the title compound (I) mapped over d norm .
ated using Crystal Explorer 21.5 (Spackman et al., 2021), with a standard resolution of the 3D d norm surfaces plotted over a fixed color scale of À 0.1253 (red) to 1.4046 (blue) arbitrary units (Fig. 3).The N2-H2� � �O1 hydrogen bond was identified to be a crucial structure-forming interaction within the crystal packing.The intense red spots symbolizing short contacts and negative d norm values on the surface are related to the presence of the N2-H2� � �O1 hydrogen bonds in the crystal structure.The weak C4-H4� � �O2 contacts are indicated by faint red spots (Fig. 4).The 2D fingerprint plots for the H� � �O/O� � �H, H� � �H, H� � �C/C� � �H, and H� � �N/N� � �H contacts are shown in Fig. 5.The most significant interactions are H� � �O/O� � �H, which play a defining role in the overall crystal packing, contributing 43.7%, and are located in the tip and middle region of the fingerprint plot.H� � �H interactions contribute 31.0%,being located in the middle region of the fingerprint plot.The contributions of the weak H� � �C/C� � �H and H� � �N/N� � �H contacts to the Hirshfeld surface are 8.5 and 1.1%, respectively.
Shape-index and curvedness are the metrics that describe the local shape in terms of principal curvatures, representing the surface properties of the crystal molecule to determine their arrangements.The Hirshfeld surface mapped over electrostatic potential, shape-index, curvedness and fragment patches is shown in Fig. 6.The electrostatic potential map (Fig. 6a) highlights the electronegative (red) and electropositive (blue) regions in the molecule.The molecule shows red colored regions near the oxygen atom (O1), indicating the electronegative spots (Akhileshwari et al., 2021).The pattern of red and blue triangles on the shape-index map (Fig. 6b) shows feature characteristic of �-� interactions.As the molecule shows flat regions on the curvedness map (Fig. 6c), it is evident that the title molecule is arranged in planar stacking (Spackman & Jayatilaka, 2009).The fragment patches (Fig. 6d) illustrates the coordination number of the corresponding atoms in the compound.

Synthesis and crystallization
1.0 g of 2-acetyl-6-aminonaphthalene were dissolved in 35 ml of Ac 2 O, stirred for 10 minutes, and 30 ml of CH 3 COOH were added, followed by the slow addition of 6.5 ml of concentrated HNO 3 under ice-bath conditions for 3 h at room temperature.When the reaction was complete, it is extracted with CH 2 Cl 2  three times, the organic phase was combined, the positive silica gel column was passed under normal pressure after spinning (eluent CH 2 Cl 2 :ethyl acetate, 10:1).The eluent containing the product components was collected and the light-yellow solid was concentrated.It was dissolved in methanol and placed in a refrigerator at 277 to cultivate lightyellow transparent square crystals (Xu et al., 2017).The MeOH was dissolved and red transparent square crystals suitable for X-ray diffraction were were obtained at 277 K in the refrigerator.

Figure 4
Figure 4 Hirshfeld surface mapped over d norm for the title compound (I) showing: H� � �O/O� � �H (upside and downside) contacts.

Figure 5
Figure 5 The two-dimensional fingerprint plots of the title compound (I), showing (a) all interactions, and delineated into (b) H� � �H, (c) O� � �H/H� � �O, (d) C� � �H/H� � �C, and (e) N� � �H/H� � �N interactions [The d e and d i values represent the distances (in A ˚) from a point on the Hirshfeld surface to the nearest atoms inside and outside the surface, respectively.]

Table 2
Experimental details.