(E)-2-[(2-Hydroxy-5-nitrophenyl)iminiomethyl]-4-nitrophenolate

The title molecule, C13H9N3O6, consists of a 2-hydroxy-5-nitrophenyliminio group and a 4-nitrophenolate group bonded to a methylene C atom with both of the planar six-membered rings nearly in the plane of the molecule [dihedral angle = 1.3 (4)°]. Each of the nitro O atoms is twisted slightly out of the plane of the molecule. The amine group forms an intramolecular hydrogen bond with both nearby O atoms, each of which has partial occupancy of attached H atoms [0.36 (3) and 0.64 (3)]. An extended π-delocalization throughout the entire molecule exists producing a zwitterionic effect in this region of the molecule. The shortened phenolate C—O bond [1.2749 (19)°], in concert with the slightly longer phenol C—O bond [1.3316 (19) Å], provides evidence for this effect. The crystal packing is influenced by extensive strong intermolecular O—H⋯O hydrogen bonding between the depicted phenolate and hydroxy O atoms and their respective H atoms within the π-delocalized region of the molecule. As a result, molecules are linked into an infinite polymeric chain diagonally along the [110] plane of the unit cell in an alternate inverted pattern. A MOPAC AM1 calculation provides support for these observations.

The title molecule, C 13 H 9 N 3 O 6 , consists of a 2-hydroxy-5nitrophenyliminio group and a 4-nitrophenolate group bonded to a methylene C atom with both of the planar sixmembered rings nearly in the plane of the molecule [dihedral angle = 1.3 (4) ]. Each of the nitro O atoms is twisted slightly out of the plane of the molecule. The amine group forms an intramolecular hydrogen bond with both nearby O atoms, each of which has partial occupancy of attached H atoms [0.36 (3) and 0.64 (3)]. An extended -delocalization throughout the entire molecule exists producing a zwitterionic effect in this region of the molecule. The shortened phenolate C-O bond [1.2749 (19) ], in concert with the slightly longer phenol C-O bond [1.3316 (19) Å ], provides evidence for this effect. The crystal packing is influenced by extensive strong intermolecular O-HÁ Á ÁO hydrogen bonding between the depicted phenolate and hydroxy O atoms and their respective H atoms within the -delocalized region of the molecule. As a result, molecules are linked into an infinite polymeric chain diagonally along the [110] plane of the unit cell in an alternate inverted pattern. A MOPAC AM1 calculation provides support for these observations.   Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx; y þ 1 2 ; Àz þ 1 2 ; (ii) Àx; y À 1 2 ; Àz þ 1 2 ; (iii) Àx; Ày þ 2; Àz; (iv) Àx þ 1; Ày þ 1; Àz; (v) Àx þ 1; Ày; Àz; (vi) x; Ày þ 1 2 ; z þ 1 2 .

Related literature
Data collection: CrysAlisPro (Oxford Diffraction, 2007); cell refinement: CrysAlisPro; data reduction: CrysAlisPro program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.  Ersanlı et al. (2003)). Compounds of this type can be used as anion sensors in acetonitrile (Hijji et al. (2008)) that tend to exist in the keto-amine form, which is generally favored over the phenol-imine form in the solid state. Introduction of electron deficient groups to the aromatic rings tends to increase the acidity of the phenolic proton.
The title molecule, C 13 H 9 N 3 O 6 , consists of a 2-hydroxy-5-nitrophenyliminio group and a 4-nitrophenolate group bonded to a methylene carbon atom with both of the planar six-membered rings nearly in the plane of the mo-  Table 2). There appears to be an extended π delocalization effect throughout the entire molecule producing a zwitterionic effect in this region of the molecule. The shortened C1-O1 bond (1.2749 (19) Å in concert with the slightly longer C9-O2 bond (1.3316 (19) Å) provide structural evidence for this effect. and phenolate (C3) groups (Fig. 2), respectively. All of the hydrogen bond interactions are summarized in Table 1. As a result the molecules are linked into an infinite polymeric chain diagonally along the [110] plane of the unit cell in an alternate inverted pattern (Fig. 2). In addition, weak Cg1-Cg1 (3.517 (2) Å; slippage = 1.09 (8)°; -x, 1 -y, -z) and Cg1-Cg2 (3.830 (6) Å; x, y -1, z) π-π stacking ring interactions also occur where Cg1 = center of gravity of the C1-C6 ring and Cg2 = center of gravity of the C8-C13 ring.
After a MOPAC AMI calculation [Austin Model 1 approximation together with the Hartree-Fock closed-shell (restricted) wavefunction was used and minimizations were terminated at an r.m.s. gradient of less than 0.01 kJ mol -1 Å -1 ] of the zwitterionic form with WebMO Pro (Schmidt, 2007). As a result of this energy minimization, the dihedral angle between supplementary materials sup-2 the phenyl and phenolate rings changes from 1.3 (4)° in the crystal structure to 7.6 (6)°, producing a slightly more twisted molecule than the nearly planar molecule in the crystalline environment. Thus, it is apparent that the extensive hydrogen bonding and π-π stacking intermolecular interactions significantly influence crystal packing with this molecule.

Experimental
The title compound was synthesized as follows: 2-amino-4-nitrophenol (0.15 g, 1 mmol) and 2-hydroxy-5-nitrobenzaldehyde (0.17 g, 1 mmol) were mixed in a loosely capped vial. The reaction mixture was allowed to heat at full power in a conventional microwave for 8 minutes. The compound was recrystallized from ethanol affording a brown solid (0.20 g,  90, 162.13, 157.48, 139.89, 138.76, 133.40, 128.95, 128.69, 124.51, 118.78, 118.25, 116.54, 115.24.    Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.