The interaction between 8-hydroxyquinoline (8HQ, C9H7NO) and naphthalene-1,5-disulfonic acid (H2NDS, C10H8O6S2) in aqueous media results in the formation of the salt hydrate bis(8-hydroxyquinolinium) naphthalene-1,5-disulfonate tetrahydrate, 2C9H8NO+·C10H6O6S22−·4H2O. The asymmetric unit comprises one protonated 8HQ+ cation, half of an NDS2– dianion symmetrically disposed around a center of inversion, and two water molecules. Within the crystal structure, these components are organized into chains along the [010] and [10\overline{1}] directions through O—H...O and N—H...O hydrogen-bonding interactions, forming a di-periodic network parallel to (101). Additional stabilizing interactions such as C—H...O, C—H...π, and π–π interactions extend this arrangement into a tri-periodic network structure
