A new polymorph of bis (2-amino pyridinium) fumarate-fumaric acid (1/1) from powder X-ray diffraction

A new polymorph of bis (2-amino pyridinium) fumarate-fum aric acid (1/1), 2C5H7N2 ⁺·C4H2O4 ^2-·C4H4O4, was obtained and its crystal structure determined by powder X-ray diffraction. The new polymorph (form II) crystallizes in the triclinic system (space group P ), while the previous reported polymorph [form I; Ballabh, Trivedi, Dastidar & Suresh (2002). CrystEngComm, 4, 135-142; Büyükgüngör, Odabaşoǧlu, Albayrak & Lönnecke (2004). Acta Cryst. C60, o470-o472] is monoclinic (space group P21/c). In both forms I and II, the asymmetric unit consists of one 2-amino pyridinium cation, half a fumaric acid mol ecule and half a fumarate dianion. The fumarate dianion is involved in hydrogen bonding with two neighbouring 2-amino pyridinium cations to form a hydrogen-bonded trimer in both forms. In form II, the hydrogen-bonded trimers are inter linked across centres of inversion via pairs of N - H⋯O hydrogen bonds, whereas such trimers are joined via single N - H⋯O hydrogen bonds in form I, leading to different packing modes for forms I and II. The results demonstrate the relevance and application of the powder diffraction method in the study of polymorphism of organic mol ecular materials.