In the title co-crystal, C7H5NO4. C5H4N2O3, the two components are linked b
y an intermolecular hydrogen band between the O-H and N-O groups [O ... O 2
.577(3) Angstrom]. The interplanar angle between the planes of the rings of
the molecules is 5.3 (2)degrees. The rings are stacked in the crystal with
a mean interplanar distance of 3.279 (3) Angstrom.