Crystal engineering: co-crystals of cinnamic acid derivatives with a pyridyl derivative co-crystalliser

Abstract A number of hydrogen-bonded co-crystals, consisting of a cinnamic acid derivative and a pyridyl co-crystalliser, have been synthesised and their properties investigated by X-ray diffraction. Samples were prepared by recrystallisation or solvent drop grinding of trans-cinnamic acid (1), 4-methylcinnamic acid (2), 4-methoxy cinnamic acid (3) or 3,4-methoxy cinnamic acid (4), with 4,4-dipyridyl (A), iso-nicotinamide (B) or nicotinamide (C). The X-ray single crystal structures of seven novel co-crystals, obtained through recrystallisation, are examined and the hydrogen bonding interactions discussed. Consistent hydrogen bonding motifs were observed for samples prepared when using 4,4-dipyridyl (A) or iso-nicotinamide (B) as the co-crystallising agent. Powder X-ray diffraction analysis of the samples prepared by solvent drop grinding suggests the formation of ten co-crystals.