4-Pyridone-terephthalic acid-water (2/1/2) and bis(3-hydroxypyridinium) terephthalate.

4-Hydroxypyridine and terephthalic acid cocrystallize as a hydrate, 4-pyridone-terephthalic acid-water (2/1/2), 2C(5)H(5)NO·C(8)H(6)O(4)·2H(2)O, from a methanol-water solution. The molecules form a two-dimensional hydrogen-bonded network resulting in sheets of hydrogen-bonded molecules that lie parallel to the (10-2) plane. In contrast, 3-hydroxypyridine and terephthalic acid form the salt bis(3-hydroxypyridinium) terephthalate, 2C(5)H(6)NO(+)·C(8)H(4)O(4)(2-), giving rise to two-dimensional hydrogen-bonded sheets extending through the lattice parallel to the (102) plane.