C–H ⋯ O hydrogen bonding and topochemistry in crystalline 3,5-dinitrocinnamic acid and its 1 : 1 donor–acceptor complex with 2,5-dimethoxycinnamic acid

Abstract
3,5-Dinitrocinnamic acid adopts an unusual crystal structure wherein C–H ⋯ O hydrogen bonds dictate the symmetry of the O–H ⋯ O network while its 1 : 1 molecular complex with 2, 5-dimethoxycinnamic acid is photoreactive in the solid state to yield an unsymmetrical cyclobutane dimer.