(Z)-6-{2-[(E)-2,4-Dihydroxy­benzyl­ideneamino]phenyl­amino­methyl­ene}-3-hydroxy­cyclo­hexa-2,4-dienone toluene solvate

The bis-Schiff base title compound, C(20)H(16)N(2)O(4)·C(7)H(8), crystallized as a toluene solvate. In the solid state, it is present as its prototropic tautomer formed by transfer of one of the ortho-hydroxyl H atoms. The proton transfer is accompanied by a shift of electron pairs, as is evident from the observed C—O and C—N bond distances of 1.305 (2) and 1.315 (2) Å, which are largely consistent with C=O and C—N distances. The actual mol­ecule present in the solid state is thus the charge-neutral β-keto amine, with a small contribution of its zwitterionic valence tautomer via partial delocalization of electron pairs along the N—C—C—C—O atom chain. The dihedral angles between the central benzene ring and the two outer benzene rings of the Schiff base are 51.99 (8) and 12.95 (9)°. Intra­molecular O—H⋯N and N—H⋯O hydrogen bonds generate S(6) ring motifs, whereas intra­molecular N—H⋯N hydrogen bonds generate S(5) ring motifs. In the crystal structure, O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions link the mol­ecules into one-dimensional zigzag chains along the b axis; these chains are further stacked by O—H⋯O and weak C—H⋯O inter­actions along the c axis, forming two-dimensional extended networks parallel to the bc plane. In addition, the crystal structure is further stabilized by weak C—H⋯π and π–π inter­actions.