title: 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 group P-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 group P2₁/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 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 molecular materials.
authors.affiliation: College of Materials Science and Engineering, Nanjing University of Technology, No. 5 Xinmofan Road, Nanjing, People's Republic of China.
authors.forename: Shuichao
authors.initials: S
authors.lastname: Dong
authors.forename: Yaqiu
authors.initials: Y
authors.lastname: Tao
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Shen
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Pan
keywords: crystal structure; fumarates; organic salts; polymorphs