Experimental

R factor = 0.045; wR factor = 0.125; data-to-parameter ratio = 16.7. The title 1:1 co-crystal, C6H12N2C6H6O4, the dicarboxylic acid molecule is close to planar [r.m.s. deviation from the mean plane = 0.07 (1) Å]. In the crystal, the two molecules are arranged alternately and are linked by O—H N hydrogen bonds, leading to the formation of a chain along the [201] direction. The chains are assembled into a two-dimensional framework parallel to the (102) plane through weak C— H O hydrogen bonds between the two types of molecules