Crystal structure of 4-oxo-4H-chromene-3-carb-oxy-lic acid

In the title compound, C10H6O4, also known as 3-carb-oxy-chromone, the non-H atoms of the chromone ring are essentially coplanar (r.m.s. deviation = 0.0057 Å), with the maximum deviation from their least-squares plane [0.011 (2) Å] being for a pyran C atom. The dihedral angle between the fused ring and plane of the carb-oxy group is 3.06 (2)°. An intra-molecular hydrogen bond is formed between the ring carbonyl O atom and the carb-oxy O-H atom, closing an S(6) loop. In the crystal, mol-ecules are assembled by stacking inter-actions [centroid-centroid distance between the benzene and pyran rings = 3.844 (3) Å] and C-H⋯O hydrogen bonds, generating a three-dimensional network. Short contacts are also observed between the carb-oxy O and C atoms [C=O⋯C=O = 3.002 (3) Å].