2-Carboxylatopyridinium-4-nitrophenol (1/1)

In the title 1:1 adduct, C6H5NO3 center dot C6H5NO2, both molecules are almost planar (r.m.s. deviations for the non-H atoms = 0.027 and 0.023 angstrom for 4-nitrophenol and 2-carboxyl-atopyridinium, respectively). The pyridine molecule crystallizes as a zwitterion (nominal proton transfer from the carboxylic acid group to the N atom in the ring). In the crystal, inversion dimers of the zwitterions linked by pairs of N-H...O hydrogen bonds generate R-2(2) (10) loops; two 4-nitrophenol molecules link to the dimer by O-H...O hydrogen bonds, generating a four-molecule aggregate. These are linked by C-H...O interactions, forming a three-dimensional network.