organic compounds
The crystal structures of diammonium fumarate, 2NH4+.C4H2O42−, (I) and bis(isopropylammonium) fumarate, 2C3H7NH3+.C4H2O42−, (II), have been determined. The intermolecular N-HO hydrogen bonds form a three-dimensional network in (I), whereas two-dimensional sheets are formed in (II) and separated by layers of isopropyl groups. The NO distances are 2.790 (1)–2.903 (1) Å in (I) and 2.747 (1)–2.807 (1) Å in (II). Differences between the solid-state photoreactivities of the fumaric acid ions in (I) and (II) are rationalized based on the crystal structures.