(E)-4-Hydroxy-2-[(2-hydroxyphenyl)iminiomethyl]phenolate

The title compound, C(13)H(11)NO(3), crystallizes in a zwitterionic form and has a trans configuration about the C=N bond. The molecule is almost planar, the dihedral angle between the two benzene rings being 4.32 (8)degrees. The two hydroxy substituents are coplanar with each of their attached benzene rings [r.m.s. deviations of 0.0053 (2) and 0.0052 (2) angstrom]. An intramolecular N-H center dot center dot center dot O hydrogen bond formed between the iminium N and the phenolate O atom generates an S(6) ring motif. In the crystal, the molecules are linked through O-H center dot center dot center dot O hydrogen bonds into chains along [110]. Two neighbouring chains are further connected through O-H center dot center dot center dot O hydrogen bonds in an antiparallel manner. pi-pi interactions are also observed, with centroid-centroid distances of 3.7115 (19) and 3.743 (2) angstrom.