Benzene-1,3,5-tri-carb-oxy-lic acid-pyridinium-2-olate (1/3).

The asymmetric unit of the title compound, C9H6O6·3C5H5NO, contains one benzene-1,3,5-tri-carb-oxy-lic acid mol-ecule (BTA) and three pyridin-2-ol mol-ecules each present in the zwitterion form. In the crystal, these entities are linked through O-H⋯O(-) and N(+)-H⋯O(-) hydrogen bonds, forming sheets parallel to (10-1). These layers contain macrocyclic rings of composition [BTA]2[pyol]6 and with graph-set notation R (6) 8(44), which are stacked along c through π-π inter-actions [inter-centroid distances = 3.536 (2)-3.948 (3) Å]. They are inter-connected by N(+)-H⋯O(-) hydrogen-bonded chains of pyridin-2-ol mol-ecules running parallel to c, forming a three-dimensional network. There are also C-H⋯O hydrogen bonds present which reinforce the three-dimensional structure.