(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)°. 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) Å]. An intra­molecular N—H⋯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⋯O hydrogen bonds into chains along [110]. Two neighbouring chains are further connected through O—H⋯O hydrogen bonds in an anti­parallel manner. π–π inter­actions are also observed, with centroid–centroid distances of 3.7115 (19) and 3.743 (2) Å.