Zwitterionic (E)-1-[(4-nitrophenyl)iminiomethyl]naphthalen-2-olate

The title compound, C17H12N2O3, was synthesized by the reaction of 2-hydroxy-1-naphthaldehyde with 4-nitrobenzenamine. These condense to form the Schiff base, which crystallizes in the zwitterionic form. In the structure, the keto–amino tautomer has a fairly short intramolecular N—H⋯O hydrogen bond between the 2-naphthalenone and amino groups, with electron delocalization. The molecule is essentially planar, with a dihedral angle of 1.96 (3)° between the ring systems. In the crystal, the molecules are linked via intermolecular C—H⋯O hydrogen bonds, forming a layer parallel to (101).

As part of our ongoing studies of Schiff base complexes and derivatives we report here synthesis and the crystal structure of the title compound, obtained by the reaction of 2-hydroxy-1-naphthaldehyde with 4-nitroaniline, which crystallized in a zwitterionic form with cationic iminium and anionic naphtholate group.
The molecular structure of (I), and the atomic numbering used, is illustrated in Fig. 1. All bond distances and angles are within the ranges of accepted values (CSD, Allen, 2002) and in literature Nadeem et al., 2009;Eltayeb et al., 2008).
The main molecule is essentially planar with an rms deviation of 0.0350 Å, and the crystal structure exhibit alternating layers parallel to (101) plane (Fig. 2). In the crystal, molecules are linked via intermolecular C-H···O hydrogen bonds to form a two-dimensional layers parallel to (101) ( Table 1, Fig. 3) and additional stabilization within these layers is provided by N-O···π and π···π stacking interactions. These interaction bonds link the molecules within the layers and also link the layers together and reinforcing the cohesion of the structure. An intramolecular N-H···O hydrogen bond occurs.

Experimental
The title compound, (I), was prepared by refluxing a mixture of a solution containing (0.1 mmol) of 2-hydroxy-1-naphthaldehyde and (0.1 mmol) of 4-nitrobenzenamine in 20 ml methanol. The reaction mixture was stirred for 1 h under reflux.
Microcrystals of (I) were obtained by allowing the clear solution to stand overnight. The powder product was dissolved and recrystallized from DMSO solution. Some red crystals were carefully isolated under polarizing microscope for analysis by x-ray diffraction.

Refinement
H7 and H2N were located in difference Fourier maps and refined isotropically. The remaining H atoms were localized on Fourier maps but introduced in calculated positions and treated as riding on their parent atoms (C aryl ) with C aryl -H aryl =0.95Å and U iso (H aryl )=1.2U eq (C aryl ).
supplementary materials sup-2 Figures Fig. 1. (Farrugia, 1997) The asymmetric unit of the title compound with the atomic labeling scheme. Displacement are drawn at the 50% probability level. Hydrogen bond shown as dashed line.