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

Abstract

A new polymorph of bis(2-aminopyridinium) fumarate–fumaric acid (1/1), 2C5H7N2+·C4H2O42−·C4H4O4, was obtained and its crystal structure determined by powder X-ray diffraction. The new polymorph (form II) crystallizes in the triclinic system (space groupP\overline{1}), while the previous reported polymorph [form I; Ballabh, Trivedi, Dastidar & Suresh (2002).CrystEngComm,4, 135–142; Büyükgüngör, Odabaşoğlu, Albayrak & Lönnecke (2004).Acta Cryst.C60, o470–o472] is monoclinic (space groupP21/c). In both forms I and II, the asymmetric unit consists of one 2-aminopyridinium cation, half a fumaric acid molecule and half a fumarate dianion. The fumarate dianion is involved in hydrogen bonding with two neighbouring 2-aminopyridinium cations to form a hydrogen-bonded trimer in both forms. In form II, the hydrogen-bonded trimers are interlinked across centres of inversionviapairs of N—H...O hydrogen bonds, whereas such trimers are joinedviasingle 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 molecular materials.