Each mol­ecule of the title compound, C12H18N4O6, is located on an inversion centre at the mid-point of the central N—N bond. The azo groups C=N of the Schiff base group have an E conformation and the azo groups in the oxime C=N—O groups have a Z conformation. O–H⋯O hydrogen bonds link neighbouring mol­ecules into infinite monolayers perpendicular to the a axis.

The title compound, C19H12N2O3, has two independent mol­ecules (A and B) in the asymmetric unit. There is an intra­molecular O—H⋯N hydrogen bond in each mol­ecule. The mean planes of the naphthalene [maximum deviations = 0.024 (3) and 0.030 (3) Å in A and B, respectively] and the isoindoline units [maximum deviations 0.009 (3) and 0.008 (3) Å in A and B, respectively] are almostly coplanar, with dihedral angles of 4.25 (9) ad 3.84 (9)° in mol­ecules A and B, respectively. The two independent mol­ecules are connected by π–π inter­actions [centroid-centroid distances 3.5527 (19) and 3.5627 (19) Å]. In the crystal, the A+B pairs are further connected via π–π inter­actions [centroid–centroid distances = 3.693 (2)–3.831 (2) Å], leading to the formation of columns propagating along the a-axis direction. The columns are linked via C—H⋯O inter­actions, leading to the formation of a three-dimensional network.

The title mol­ecule, C40H30, lies on an inversion center. The two unique phenyl rings form dihedral angles of 51.98 (8) and 67.58 (8)° with the essentially planar biphenyl unit [maximum deviation = 0.0360 (14) Å].