(Z)-6-{2-[(E)-2,4-Dihydroxy-benzyl-ideneamino]phenyl-amino-methyl-ene}-3-hydroxy-cyclo-hexa-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 mol-ecule 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)°. Intra-molecular O-H⋯N and N-H⋯O hydrogen bonds generate S(6) ring motifs, whereas intra-molecular N-H⋯N hydrogen bonds generate S(5) ring motifs. In the crystal structure, O-H⋯O hydrogen bonds and weak C-H⋯O inter-actions link the mol-ecules into one-dimensional zigzag chains along the b axis; these chains are further stacked by O-H⋯O and weak C-H⋯O inter-actions 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 inter-actions.