(E)-2-[(2-Hydr-oxy-5-nitro-phen-yl)iminiometh-yl]-4-nitro-phenolate.

The title mol-ecule, C(13)H(9)N(3)O(6), consists of a 2-hydr-oxy-5-nitro-phenyl-iminio group and a 4-nitro-phenolate group bonded to a methyl-ene C atom with both of the planar six-membered rings nearly in the plane of the mol-ecule [dihedral angle = 1.3 (4)°]. Each of the nitro O atoms is twisted slightly out of the plane of the mol-ecule. The amine group forms an intra-molecular 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 mol-ecule exists producing a zwitterionic effect in this region of the mol-ecule. 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 inter-molecular O-H⋯O hydrogen bonding between the depicted phenolate and hydr-oxy O atoms and their respective H atoms within the π-delocalized region of the mol-ecule. As a result, mol-ecules 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.