(E)-2-[(2-Hydroxy-5-nitrophenyl)iminiomethyl]phenolate

In the title molecule, C13H10N2O4, the dihedral angle between the mean planes of the benzene and phenolate rings is 21.6 (4)degrees. The nitro O atoms are twisted slightly out of the plane of the ring to which the nitro group is attached [dihedral angle 8.4 (3)degrees]. The amine group forms an intramolecular hydrogen bond with both nearby O atoms. An extended pi delocalization throughout the entire molecule exists producing a zwitterionic effect in this region of the molecule. The shortened C-O bond [1.2997 (15) angstrom] in concert with the slightly longer C-OH bond [1.3310 (16) angstrom] provide evidence for this effect. The crystal packing is influenced by strong intermolecular O-H center dot center dot center dot O hydrogen bonding. As a result, molecules are linked into an infinite zigzag chain running along the b axis. A MOPAC PM3 calculation provides support to these observations.