Unlocking pedal motion of the azo group: three- and unexpected eight-component hydrogen-bonded assemblies in co-crystals based on isosteric resorcinols

Co-crystallization of 3-phenylazopyridine (3PAzP) with dihalogenated resorcinols (res) 4,6-diX res (where: X = Cl, Br, and I) yields co-crystals that support molecular pedal motion in the crystalline state. The co-crystals are sustained by hydrogen-bonded assemblies, with the pattern of hydrogen-bonding drastically different based on the res. For 4,6-diCl res, an unexpected eight-component hydrogen-bonded assembly is realized, while three-component hydrogen-bonded assemblies are observed for 4,6-diBr res and 4,6-diI res. We show the co-crystallization approach to afford pedal motion in the azo core, while no such motion is present in the absence of a res. Pure 3PAzP packs to form a noncentrosymmetric herringbone structure.