Bis(8-hydroxy­quinolinium) squarate

The title compound, 2C₉H₈NO₂⁺·C₄O₄²⁻, contains a dianion with approximately D_4h symmetry [C—C = 1.465 (4)–1.470 (4) Å and C—O = 1.248 (4)–1.264 (4) Å]. Individual dianions are linked to four neighbouring 8-hydroxy­quinolinium cations by O...H—N [2.666 (4) and 2.681 (4) Å] and O...H—O [2.596 (3) and 2.605 (3) Å] hydrogen bonds to generate a polymeric chain.