2,6-Dihy­droxy-4-oxo-2-(pyridin-1-ium-3-yl)-4H-1,3,2-benzodioxaborinin-2-ide 0.67-hydrate

The asymmetric unit of the title compound, C₁₂H₁₀BNO₅·0.67H₂O, contains three independent pyridinylboronic acid esters adopting zwitterionic forms and two water mol­ecules. The six-membered heterocyclic rings in the boronic esters have half-chair conformations and the deviations of the B atoms from the boronate mean planes range from 0.456 (3) to 0.657 (3) Å. All of the B atoms have tetra­hedral coordination environments, with B—O and B—C bond lengths of 1.446 (4)–1.539 (3) and 1.590 (5)–1.609 (5) Å, respectively. In the crystal, the ester and water mol­ecules are linked into a three-dimensional network by a large number of O—H...O, N—H...O and C—H...O hydrogen bonds. The crystal packing is further accomplished by π–π inter­actions, with centroid–centroid distances of 3.621 (4)–3.787 (4) Å.

Benzene-1,3,5-tri­carb­oxy­lic acid–pyridinium-2-olate (1/3)

The asymmetric unit of the title compound, C₉H₆O₆·3C₅H₅NO, contains one benzene-1,3,5-tri­carb­oxy­lic acid mol­ecule (BTA) and three pyridin-2-ol mol­ecules 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 R⁶₈(44), which are stacked along c through π–π inter­actions [inter-centroid distances = 3.536 (2)–3.948 (3) Å]. They are inter­connected by N⁺—H...O⁻ hydrogen-bonded chains of pyridin-2-ol mol­ecules running parallel to c, forming a three-dimensional network. There are also C—H...O hydrogen bonds present which reinforce the three-dimensional structure.