Hydrogen-bonded networks in trans-3-(3-pyrid­yl)acrylic acid and rctt-3,3′-(3,4-dicarboxy­cyclo­butane-1,2-diyl)­dipyridinium dichloride

The structure of trans-3-(3-pyridyl)acrylic acid, C₈H₇NO₂, (I), possesses a two-dimensional hydrogen-bonded array of supra­molecular ribbons assembled via heterodimeric synthons between the pyridine and carboxyl groups. This compound is photoreactive in the solid state as a result of close contacts between the double bonds of neighbouring mol­ecules [3.821 (1) Å] along the a axis. The crystal structure of the photoproduct, rctt-3,3′-(3,4-dicarboxy­cyclo­butane-1,2-diyl)­dipyridinium dichloride, C₁₆H₁₆N₂O₄²⁺·2Cl⁻, (II), consists of a three-dimensional hydrogen-bonded network built from crosslinking of helical chains integrated by self-assembly of dipyridinium cations and Cl⁻ anions via different O—H...Cl, C—H...Cl and N⁺—H...Cl hydrogen-bond inter­actions.