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 intra-molecular O-H⋯O hydrogen bond, which forms an S(6) ring motif. The hy-droxy group of the oxine unit makes a hydrogen bond with the one of the O atoms of the carboxyl-ate group of the 2-carb-oxy-acetate anion. Two other carboxyl-ate O atoms form R(2) (2)(7) ring motifs via inter-molecular C-H⋯O and N-H⋯O hydrogen bonds. The crystal structure is consolidated by weak inter-molecular C-H⋯O inter-actions, which link the cations and anions into a three-dimensional network.