(E)-N′-(2,3,4-Trihy­droxy­benzyl­idene)­isonicotinohydrazide dihydrate

In the title isoniazid derivative, C(13)H(11)N(3)O(4)·2H(2)O, the Schiff base mol­ecule exists in an E configuration with respect to the acyclic C=N bond. An intra­molecular O—H⋯N hydrogen bond forms a six-membered ring, producing an S(6) ring motif. The essentially planar pyridine ring [maximum deviation = 0.0119 (8) Å] is inclined at a dihedral angle of 7.30 (4)° with respect to the benzene ring. In the crystal, inter­molecular O—H⋯N, O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds link the mol­ecules into two-dimensional arrays lying parallel to the (10[Image: see text]) plane. These arrays are further inter­connected into a three-dimensional extended network via O—H⋯O and C—H⋯O hydrogen bonds. A weak inter­molecular π–π inter­action [centroid-to-centroid distance = 3.5627 (5) Å] is also observed.