8-Hy­droxy­quinolinium 2-carb­oxy­acetate

In the title compound, C(9)H(8)NO(+)·C(3)H(3)O(4) (−), the cation and anion are each essentially planar, with maximum deviations of 0.043 (1) and 0.060 (1) Å, respectively. The dihedral angle between these two planes is 2.20 (4)°. The conformation of the anion is stabilized by an intra­molecular O—H⋯O hydrogen bond, which forms an S(6) ring motif. The hy­droxy group of the oxine unit makes a hydrogen bond with the one of the O atoms of the carboxyl­ate group of the 2-carb­oxy­acetate anion. Two other carboxyl­ate O atoms form R (2) (2)(7) ring motifs via inter­molecular C—H⋯O and N—H⋯O hydrogen bonds. The crystal structure is consolidated by weak inter­molecular C—H⋯O inter­actions, which link the cations and anions into a three-dimensional network.