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The whole molecule of the title Schiff base compound, C28H28N2O2, is generated by inversion symmetry. It is formed from two units of ortho-hy­droxy­naphthaldehyde bridged with 1,6-di­amino­hexane. The N atoms are protonated and, thus, the structure is a bis-zwitterionic compound in the solid state. The zwitterion shows strong intra­molecular N—H⋯O hydrogen bonds between the iminium N and the naphthaleno­late O atoms.

In the title compound, C20H14Br2N2O2, there are two intramolecular O—H...N hydrogen bonds formingS(6) ring motifs. The outer benzene rings are inclined to the central benzene ring by 39.09 (11) and 24.31 (11)°, and to one another by 37.12 (11)°. In the crystal, molecules are linked by a short Br...O contact [3.1307 (19) Å], forming zigzag chains propagating along thea-axis direction. The chains are linked by weak offset π–π interactions [intercentroid distance = 3.716 (1) Å], forming layers parallel to theacplane.

The title compound, C34H40N2O2, exists in an extended conformation and has crystallographically imposed centrosymmetry. The crystal packing can be described as being composed of parallel layers stacked along [010]. The zwitterionic structure is stabilized by an intra­molecular N—H⋯O hydrogen-bond inter­action.